Tps 2377
Tps 2377
TPS2375
                                                                                                                                                                                             TPS2376
                                                                                                   D8       PW8                                                                            TPS2377
www.ti.com............................................................................................................................................................ SLVS525B  APRIL 2004  REVISED APRIL 2008
DESCRIPTION
These easy-to-use 8-pin integrated circuits contain all of the features needed to develop an IEEE 802.3af
compliant powered device (PD). The TPS2375 family is a second generation PDC (PD Controller) featuring
100-V ratings and a true open-drain, power-good function.
In addition to the basic functions of detection, classification and undervoltage lockout (UVLO), these controllers
include an adjustable inrush limiting feature. The TPS2375 has 802.3af compliant UVLO limits, the TPS2377 has
legacy UVLO limits, and the TPS2376 has a programmable UVLO with a dedicated input pin.
The TPS2375 family specifications incorporate a voltage offset of 1.5 V between its limits and the IEEE 802.3af
specifications to accommodate the required input diode bridges used to make the PD polarity insensitive.
Additional resources can be found on the TI Web site www.ti.com.
     RJ45
     1
              TX
                                     Data to
                                                                                                                                                        Detect        Classify Power Up & Inrush
             Pair
                                    Ethernet
                                      PHY
    2
                                                                                                                                                         Class 3
                                                                                                                                           Input         Current
                     DF01S                                                                                                                Current
                    2 Places
                                                                                   VDD
                                                                R(DET)                                100
                                                                24.9 kW,                              kW                                                                 V (PG-RTN)
                                                   SMAJ58A
                                                                1%
                                                                           DET               PG
                                                                                                                 CONVERTER
                                                                                                                  TO DC/DC
                                                                           ILIM
                                                                                   TPS2375
                                                             R(ILIM)
     4                                         0.1mF,
     5
                                                             178 kW,                               100 mF,                                                                                          VDD
                                               100 V         1%
              Spare                            10 %                                                100 V
               Pair                                                        CLASS
     7                                                                                       RTN                                                                                             VRTN
                                                                                   VSS
                                                               R(ICLASS)
     8                                                         357 W,
              Spare
               Pair                                            1%
    3
               RX
                                                                  Note: Class 3 PD Depicted.                                        Note: All Voltages With Respect to VSS.
                                          Data to                       PG Pullup Resistor Is Optional.
              Pair
                                       Ethernet PHY
             Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
             Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PRODUCTION DATA information is current as of publication date.                                                                           Copyright  20042008, Texas Instruments Incorporated
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
                                                                                              data sheet
TPS2375
TPS2376
TPS2377
SLVS525B  APRIL 2004  REVISED APRIL 2008............................................................................................................................................................ www.ti.com
              This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
              appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
              ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
              susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
AVAILABLE OPTIONS
                                                UVLO THRESHOLDS (NOMINAL)                                                                  PACKAGE (1)
            TA                                                                                                                                                                            MARKING
                                        TYPE                          LOW                           HIGH                          SO-8                       TSSOP-8
                                       802.3af                       30.5 V                         39.3 V                    TPS2375D                    TPS2375PW                           2375
      -40C to 85C                  Adjustable                      1.93 V                         2.49 V                    TPS2376D                    TPS2376PW                           2376
                                       Legacy                        30.5 V                         35.1 V                    TPS2377D                    TPS2377PW                           2377
(1) Add an R suffix to the device type for tape and reel.
(1)     Stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. These are stress ratings
        only, and functional operation of the device at these or any other conditions beyond those indicated under recommended operating
        conditions is not implied. Exposure to absolutemaximumrated conditions for extended periods may affect device reliability.
(2)     I(RTN) = 0
(3)     SOA limited to V(RTN) = 80 V and I(RTN) = 515 mA.
(4)     Surges applied to RJ-45 of Figure 1 between pins of RJ-45, and between pins and output voltage rails per EN61000-4-2, 1999.
                        (1)     Tested per JEDEC JESD51. High-K is a (2 signal  2 plane) test board and low-K is a double sided
                                board with minimum pad area and natural convection.
ELECTRICAL CHARACTERISTICS
V(VDD) = 48 V, R(DET) = 24.9 k, R(CLASS) = 255 , R(ILIM) = 178 k, and 40C  TJ  125C, unless otherwise noted. Positive
currents are into pins. V(UVLO) = 0 V for classification and V(UVLO) = 5 V otherwise for the TPS2376. Typical values are at 25C.
All voltages are with respect to VSS unless otherwise noted.
                           PARAMETER                                                        TEST CONDITIONS                                        MIN                TYP             MAX           UNIT
 DETECTION
                                                                           DET open, V(VDD) = V(RTN) = 1.9 V, measure
                      Offset current                                                                                                                                    0.3                3         A
                                                                           I(VDD) + I(RTN)
                                                                           DET open, V(VDD) = V(RTN) = 10.1 V, measure
                      Sleep current                                                                                                                                       4               12         A
                                                                           I(VDD) + I(RTN)
                      DET leakage current                                  V(DET) = V(VDD) = 57 V, measure I(DET)                                                       0.1                5         A
                                                                           V(RTN) = V(VDD),                    V(VDD) = 1.4 V                      53.7                 56             58.3          A
                                                                           R(DET) = 24.9 k,
                      Detection current
                                                                           measure I(VDD) + I(RTN) +           V(VDD) = 10.1 V                      395                410               417         A
                                                                           I(DET)
 CLASSIFICATION
                                                                           R(CLASS) = 4420 , 13  V(VDD)  21 V                                    2.2                 2.4              2.8
                                                                           R(CLASS) = 953 , 13  V(VDD)  21 V                                    10.3               10.6             11.3
 I(CLASS)             Classification current (1)                           R(CLASS) = 549 , 13  V(VDD)  21 V                                    17.7               18.3             19.5          mA
                                                                           R(CLASS) = 357 , 13  V(VDD)  21 V                                    27.1               28.0             29.5
                                                                           R(CLASS) = 255 , 13  V(VDD)  21 V                                    38.0               39.4             41.2
 V(CL_ON)             Classification lower threshold                       Regulator turns on, V(VDD) rising                                       10.2               11.3             13.0            V
 V(CU_OFF)                                                                 Regulator turns off, V(VDD) rising                                        21               21.9                23           V
                      Classification upper threshold
 V(CU_H)                                                                   Hysteresis                                                               0.5               0.78                 1           V
                      Leakage current                                      V(CLASS) = 0 V, V(VDD) = 57 V                                                                                   1         A
 PASS DEVICE
 rDS(on)              On resistance                                        I(RTN) = 300 mA                                                                            0.58               1.0           
                                                                           V(VDD) = V(RTN) = 30 V,                                                                                        15
                      Leakage current                                                                                                                                                                A
                                                                           V(UVLO) = 0 V (TPS2376)
                      Current limit                                        V(RTN) = 1 V                                                             405                461               515         mA
 I(LIM)               Inrush limit                                         V(RTN) = 2 V, R(ILIM) = 178 k                                           100                130               180         mA
                                                        (2)                V(RTN) falling, R(ILIM) = 178 k, inrush                                85%                91%            100%
                      Inrush current termination
                                                                           statenormal operation
                                                                           R(ILIM) = 69.8 k, V(RTN-VSS) = 5 V,                                      15                 25
                      Current rise time into inrush                        I(RTN) = 30 mA300 mA, V(VDD) increasing                                                                                    s
                                                                           past upper UVLO
                                                                           Apply load 20 , time measured to                                                           2              2.5
                      Current limit response time                                                                                                                                                      s
                                                                           I(RTN) = 45 mA
                      Leakage current, ILIM                                V(VDD) = 15 V, V(UVLO) = 0 V                                                                                    1         A
(1)       Classification is tested with exact resistor values. A 1% tolerance classification resistor assures compliance with IEEE 802.3af limits.
(2)       This parameter specifies the RTN current value, as a percentage of the steady state inrush current, below which it must fall to make PG
          assert (open-drain).
                                                                                   DEVICE INFORMATION
                                                                             FUNCTIONAL BLOCK DIAGRAM
                                                                                                                                                                                 DET
                                                                                                                                                                                  3
                                                             Detection
                                                            Comparator
                                               12 V
                                                        +
                           VDD
                            8                           
                                                                                                                                                                               CLASS
                                              Classification                                          10 V
                                              Comparator                                                                                                                         2
                                                                                                    Regulator
                                               22 V                                                                                                                              PG
                                                        +
                                                                             PG Comparator                                                                                        6
                                                                                                                    Delay
                                                                     1.5 V                                          150 mS
                                                                    & 10 V
                                                                                   +
                                                                                                       R
                                                   S        Q                                                    0 = Fault
                                                                0 = Inrush
                                                                                                       S    Q
                                                    R
                                                                UVLO                                                                                                            RTN
                                                                Comp.                                                                                                            5
                                                   2.5 V                                                             Thermal Shutdown,
                                                                                                                    Counter, and Latch
                         UVLO                                   +
                        76 Only                                                                      1 = Limiting
                                                 See            Current
                            7                   Note                                           45 mV 1                                           +
                                                                 Mirror                                                                                  EN
                                               2.5 V                         1:1
                                                     +                                                                                                 Current
                          ILIM                                                                          0                                              Limit Amp.
                            1                                                         800 W
                         VSS                                                                                                                                0.08 W
                           4
Note: For the TPS2376, the UVLO comparator connects to the UVLO pin and not to the UVLO divider.
                                                                                 TERMINAL FUNCTIONS
                                         PIN NUMBER
    PIN NAME                                                                      I/O          DESCRIPTION
                            TPS2375/77                 TPS2376
                                                                                               Connect a resistor from ILIM to VSS to set the start-up inrush current limit.
 ILIM                               1                        1                     O           The equation for calculating the resistor is shown in the detailed pin
                                                                                               description section for ILIM.
                                                                                               Connect a resistor from CLASS to VSS to set the classification of the
 CLASS                              2                        2                     O           powered device (PD). The IEEE classification levels and corresponding
                                                                                               resistor values are shown in Table 1.
                                                                                               Connect a 24.9-k detection resistor from DET to VDD for a valid PD
 DET                                3                        3                     O
                                                                                               detection.
 VSS                                4                        4                      I          Return line on the source side of the TPS2375 from the PSE.
                                                                                               Switched output side return line used as the low-side reference for the
 RTN                                5                        5                     O
                                                                                               TPS2375 load.
 PG                                 6                        6                     O           Open-drain, power-good output; active high.
                                                                                               Used only on the TPS2376. Connect a resistor divider from VDD to VSS to
 UVLO                                -                       7                      I
                                                                                               implement the adjustable UVLO feature of the TPS2376.
 NC                                 7                         -                                No connection
 VDD                                8                        8                      I          Positive line from the rectified PSE provided input.
                                                                              Table 1. CLASSIFICATION
               CLASS                              PD POWER (W)                                 R(CLASS) ()                       802.3af LIMITS (mA)                   NOTE
                   0                                 0.44  12.95                                4420 1%                                      0-4                      Default class
                   1                                  0.44  3.84                                 953 1%                                     9 - 12
                   2                                  3.84  6.49                                 549 1%                                    17 - 20
                   3                                 6.49  12.95                                 357 1%                                    26 - 30
                   4                                          -                                   255 1%                                    36 - 44                    Reserved for future use
RTN: This pin provides the switched negative power rail used by the downstream circuits. The operational and
inrush current limit control current into the pin. The PG circuit monitors the RTN voltage and also uses it as the
return for the PG pin pulldown transistor. The internal MOSFET body diode clamps VSS to RTN when voltage is
present between VDD and RTN and the PoE input is not present.
PG: This pin goes to a high resistance state when the internal MOSFET that feeds the RTN pin is enabled, and
the device is not in inrush current limiting. In all other states except detection, the PG output is pulled to RTN by
the internal open-drain transistor. Performance is assured with at least 4 V between VDD and RTN.
PG is an open-drain output; therefore, it may require a pullup resistor or other interface.
UVLO: This pin is specific to the TPS2376; it is not internally connected on the TPS2375 and TPS2377. The
UVLO pin is used with an external resistor divider between VDD and VSS to set the upper and lower UVLO
thresholds. The hysteresis, as measured as a percentage of the upper UVLO, is the same as the TPS2375.
The TPS2376 enables the output when V(UVLO) exceeds the upper UVLO threshold. When current begins to flow,
VDD sags due to cable resistance and the dynamic resistance of the input diodes. The lower UVLO threshold
must be below the lowest voltage that the input reaches.
The TPS2376 implements adjustable UVLO thresholds, but is otherwise functionally equivalent to the TPS2375.
The TPS2375 offers fixed UVLO thresholds designed to maximize hysteresis while maintaining compatibility with
the IEEE 802.3af standard. The TPS2377 offers fixed UVLO thresholds optimized for use with legacy PoE
systems.
VDD: This is the positive input supply to the TPS2375, which is also common to downstream load circuits. This
pin provides operating power and allows the controller to monitor the line voltage to determine the mode of
operation.
                                                                                                             TYPICAL CHARACTERISTICS
                                                                                 Graphs over temperature are interpolations between the marked data points.
                                                                                                                                                                                                                                                       CLASSIFICATION TURNON
                                                                                                                                            PD DETECTION RESISTANCE                                                                                           VOLTAGE
                                                                                                                                                       vs                                                                                                        vs
                                                      I(VDD) + I(RTN) IN DETECTION                                                                    V(PI)                                                                                                TEMPERATURE
                                            6                                                                                    35                                                                                                          11.3
                                                                                                             Resistance  k 
                                            4                                                                                                                                                                                                11.2
             Current   A
                                                                                                                                 25
                                            3                 TA = 25C
                                                                                                                                 20
                                            2                                                                                                                Specification Limits                                                            11.1
                                                                                                                                 15
                                            1
                                                                                     TA = 40C
                                            0                                                                                    10                                                                                                          11.0
                                                 0    1   2    3   4    5        6   7    8    9    10 11                               1          3           5           7        9        11                                                     40 20   0   20   40   60   80    100 120
                                                                    V(VDD)  V                                                                                 V(PI)  V                                                                                  TA  Free-Air Temperature  C
0.200 0.6
                                         21.91
                                                                                                                                0.150                                                                                                         0.5
30.56 2.488
                                          39.4
                                                                                                                                                                                                      V (UVLO)  V
        VDD  V
                                                                                                                                30.52                                                                                                        2.487
                                                                                                                VDD  V
                                                                                                                                30.48                                                                                                        2.486
                                          39.3
30.44 2.485
                                      1.928                                                                       35.15
                                                                                                                                                                                           30.60
                                      1.927
   V (UVLO)  V
35.10
                                                                                                                                                                          VDD  V
                                                                                          VDD  V
                                      1.926                                                                                                                                                30.55
                                                                                                                  35.05
                                      1.925
                                                                                                                                                                                           30.50
                                                                                                                  35.00
                                      1.924
                                                                                                                   325                                  75 k
                                       93.5
    Percent of Inrush Limit Current
                                                                                                                   300
                                       93.0                                                                        275
                                                                                                                                                                                            435
                                                                                               I (ILIM)  mA
                                                                                                                                                                            I (RTN)  mA
                                                                                                                   250
                                       92.5
                                                                                                                   225
                                       92.0                                                                                                   125 k
                                                                                                                   200
                                                                                                                                                                                            430
                                       91.5                                                                        175
                                                                                                                   150                        178 k
                                       91.0
                                                                                                                   125
                                       90.5                                                                        100                                                                      425
                                           40 20   0   20   40   60   80   100 120                                  40 20       0    20   40   60    80     100 120                           40 20 0     20 40 60 80 100 120
                                                 TA  Free-Air Temperature  C                                                 TA  Free-Air Temperature  C                                          TA  Free-Air Temperature  C
                                                                                                                               PG DEGLITCH PERIOD
                                                                                                                                       vs
                                                                                                                                  TEMPERATURE
                                                                                                                   180
                                                                                        PG Deglitch Period  s
160
140
                                                                                                                    120
                                                                                                                      40 20       0    20   40   60    80     100 120
                                                                                                                               TA  Free-Air Temperature  C
Figure 17.
APPLICATION INFORMATION
OVERVIEW
The IEEE 802.3af specification defines a process for safely powering a PD over a cable, and then removing
power if a PD is disconnected. The process proceeds through three operational states: detection, classification,
and operation. The intent behind the process is to leave an unterminated cable unpowered while the PSE
periodically checks for a plugged-in device; this is referred to as detection. The low power levels used during
detection are unlikely to cause damage to devices not designed for PoE. If a valid PD signature is present, then
the PSE may optionally inquire how much power the PD requires; this is referred to as classification. The PD
may return a default full-power signature, or one of four other choices. Knowing the power demand of each PD
allows the PSE to intelligently allocate power between PDs, and also to protect itself against overload. The PSE
powers up a valid PD, and then monitors its output for overloads. The maintain power signature (MPS) is
presented by the powered PD to assure the PSE that it is there. The PSE monitors its output for the MPS to see
if the PD is removed, and turns the port off, if it loses the MPS. Loss of MPS returns the PSE to the initial state of
detection. Figure 18 shows the operational states as a function of PD input voltage range.
The PD input is typically an RJ-45 (8-pin) connector, referred to as the power interface (PI). PD input
requirements differ from PSE output requirements to account for voltage drops in the cable and margin. The
specification uses a cable resistance of 20  to derive the voltage limits at the PD from the PSE output
requirements. Although the standard specifies an output power of 15.4 W at the PSE output, there is only
12.95 W available at the input of the PD due to the worst case power loss in the cable.
The PSE can apply voltage either between the RX and TX pairs, or between the two spare pairs as shown in
Figure 1. The applied voltage can be of either polarity. The PSE cannot apply voltage to both paths at the same
time. The PD uses input diode bridges to accept power from any of the possible PSE configurations. The voltage
drops associated with the input bridges cause a difference between the IEEE 802.3af limits at the PI and the
TPS2375 specifications.
The PSE is required to current limit between 350 mA and 400 mA during normal operation, and it must
disconnect the PD if it draws this current for more than 75 ms. The PSE may set lower output current limits
based on the PD advertised power requirements, as discussed below.
The following discussion is intended as an aid in understanding the operation of the TPS2375, but not as a
substitute for the actual IEEE 802.3af standard. Standards change and should always be referenced when
making design decisions.
                                                                                                      Must Turn Off by 
                                                                                                                                                        Must Turn On by
                                                                                                                                    Proper Operation
                                                                                                                                                                                              Maximum Input
                                                                                                      Voltage Falling
                                                                                                                                                        Voltage Rising
                                                           Classification
Classification
                                                                                                                                    Lower Limit 
                                                           Lower Limit
                                                                               Upper Limit
                     Lower Limit
                                            Upper Limit
                     Detection
Detection
Voltage
                                                                                                                           Shut -
                                   Detect                             Classify                                                                                             Normal Operation
                                                                                                                           down
PI Voltage (V)
INTERNAL THRESHOLDS
In order to implement the PoE functionality as shown in Figure 18, the TPS2375 has a number of internal
comparators with hysteresis for stable switching between the various states. Figure 19 relates the parameters in
the Electrical Characteristics section to the PoE states. The mode labeled idle between classification and
detection implies that the DET, CLASS, PG, and RTN pins are all high impedance.
                                    Operational Mode
                                                                                                                    PD Powered
                                                                                              Idle
Classification
                                                         Detection
                                                                                                                                                                   V(VDD)
                                                                                              V(CU_H)
                                                                                                            V(UVLO_F)               V(UVLO_R)
                                                       1.4V     V(CL_ON)          V(CU_OFF)
DETECTION
This feature of IEEE 802.3af eliminates powering and potentially damaging Ethernet devices not intended for
application of 48 V. When a voltage in the range of 2.7 V to 10.1 V is applied to the PI, an incremental resistance
of 25 k signals the PSE that the PD is capable of accepting power. A PD that is capable of accepting power,
but is not ready, may present an incorrect signature intentionally. The incremental resistance is measured by
applying two different voltages to the PI and measuring the current it draws. These two test voltages must be
within the specified range and be at least 1 V apart. The incremental resistance equals the difference between
the voltages divided by the difference between the currents. The allowed range of resistance is 23.75 k to
26.25 k.
The TPS2375 is in detection mode whenever the supply voltage is below the lower classification threshold. The
TPS2375 draws a minimum of bias power in this condition, while PG and RTN are high impedance and the
circuits associated with ILIM and CLASS are disabled. The DET pin is pulled to ground during detection. Current
flowing through R(DET) to VSS (Figure 1) produces the detection signature. For most applications, a 24.9-k, 1%,
resistor is recommended. R(DET) can be a small, low-power resistor because it only sees a stress of about 5 mW.
When the input voltage rises above the 11.3 V lower classification comparator threshold, the DET pin goes to an
open-drain condition to conserve power.
The input diode bridge incremental resistance can be hundreds of ohms at the low currents seen at 2.7 V on the
PI. The bridge resistance is in series with R(DET) and increases the total resistance seen by the PSE. This varys
with the type of diode selected by the designer, and it is not usually specified on the diode data sheet. The value
of R(DET) may be adjusted downwards to accommodate a particular diode type.
CLASSIFICATION
Once the PSE has detected a PD, it may optionally classify the PD. This process allows a PSE to determine the
PD power requirements in order to allot only as much power as necessary from its fixed input power source. This
allows the PSE to power the maximum number of PDs from a particular power budget. This step is optional
because some PSEs can afford to allot the full power to every powered port.
The classification process applies a voltage between 14.5 V and 20.5 V to the input of the PD, which in turn
draws a fixed current set by R(CLASS). The PSE measures the PD current to determine which of the five available
classes (Table 1) that the PD is signalling. The total current drawn from the PSE during classification is the sum
of bias currents and current through R(CLASS). The TPS2375 disconnects R(CLASS) at voltages above the
classification range to avoid excessive power dissipation (Figure 18 and Figure 19).
The value of R(CLASS) should be chosen from the values listed in Table 1 based on the average power
requirements of the PD. The power rating of this resistor should be chosen so that it is not overstressed for the
required 75-ms classification period, during which 10 V is applied. The PD could be in classification for extended
periods during bench test conditions, or if an auxiliary power source with voltage within the classification range is
connected to the PD front end. Thermal protection may activate and turn classification off if it continues for more
than 75 ms, but the design must not rely on this function to protect the resistor.
POWER GOOD
The TPS2375 includes a power-good circuit that can be used to signal the PD circuitry that the load capacitor is
fully charged. This pin is intended for use as an enable signal for downstream circuitry. If the converter tries to
start up while inrush is active, and draws a current equal to the inrush limit, a latchup condition occurs in which
the PD never successfully starts. Using the PG pin is the safest way to assure that there are no undesired
interactions between the inrush limit, the converter startup characteristic, and the size of the bulk capacitor.
The PG pin goes to an open-drain state approximately 150 s after the inrush current falls 10% below the
regulated value. PG pulldown current is only assured when the voltage difference between VDD and RTN
exceeds 4 V. This is not a limiting factor because the dc/dc converter should not be able to run from 4 V. The PG
output is pulled to RTN whenever the MOSFET is disabled or is in inrush current limiting.
Referencing PG to RTN simplifies the interface to the downstream dc/dc converter or other circuit because it is
referenced to RTN, not VSS. Care must be used in interfacing the PG pin to the downstream circuits. The pullup
to VDD shown in Figure 1 may not be appropriate for a particular dc/dc converter interface. The PG pin connects
to an internal open-drain, 100-V transistor capable of sinking 2 mA to a voltage below 0.4 V. The PG pin can be
left open if it is not used.
THERMAL PROTECTION
The controller may overheat after operation in current-limit state or classification for an extended period of time,
or if the ambient temperature becomes excessive. The TPS2375 protects itself by disabling the RTN and CLASS
pins when the internal die temperature reaches about 140C. It automatically restarts when the die temperature
has fallen approximately 20C. If this cycle occurs eight times, then the device latches off until the supply voltage
drops below the lower classification threshold. This feature prevents the part from operating indefinitely in fault,
and ensures that the PSE recognizes the fault condition when using dc MPS. Thermal protection is active
whenever the TPS2375 is not in detection.
Figure 20 shows how the TPS2375 responds when it is enabled into a short. The TPS2375 starts in the inrush
current-limit state when the input voltage exceeds the upper UVLO limit. A power dissipation of over 5 W heats
the die from 25C to 140C in approximately 400 ms. The TPS2375 then shuts down until the die temperature
drops to about 120C, which occurs in about 20 ms. This process repeats eight times before the TPS2375
latches off. The PG pin is high because RTN is tied to VDD.
                                                                                      V(PI) = 44 V, R(ILIM) = 178 kW
~ +
                                                                ~ 
                                                                                                                            VDD
                                                                                                                                                                                               Main
                    RJ45
                                                                                                       R (DET)                                                                                DC/DC
                                                                                                                                                   22 F            DC/DC
                                                                                                                                                                                             Converter
                                                                                                                    DET                                            Converter
                                                                                                                                                                                              Output
                                                                                0.1 F
TPS237X
                                                                                                                                                                   UCC3809
                                                                                                                    ILIM                                             or
                                                                                         SMAJ58A
                                                                                                      R(ILIM)
                                                                ~ +                                                                                                UCC3813
                                                                                                                    CLASS
                                                                ~                                                                    RTN
                                                                                                                            VSS
                                Option 3                                                                   R (CLASS)
                                                                                                                                                        For Option 2,
                                                                                                                                                        The Capacitor Must Be
        Auxiliary               Option 2                                                                                                                Right At The Output
         Power                                                                                                                                          To Control The
          Input                                                                                                                                         Transients.
       Use only                 Option 1                                                                                                                            Optional
      one option
                                                                                                                                                                    Regulator
Option 1 consists of ORing power to the output of the PoE dc/dc converter. This option is preferred in cases
where PoE is added to an existing design that uses a low-voltage wall adapter. The relatively large PD
capacitance reduces the potential for harmful transients when the adapter is plugged in. The wall adapter output
may be grounded if the PD incorporates an isolated converter. This solution requires two separate regulators, but
low-voltage adapters are readily available. The PoE power can be given priority by setting its output voltage
above that from the auxiliary source.
Option 2 has the benefits that the adapter voltage may be lower than the TPS2375 UVLO, and that the bulk
capacitor shown can control voltage transients caused by plugging an adapter in. The capacitor size and location
are chosen to control the amount of ringing that can occur on this node, which can be affected by additional
filtering components specific to a dc/dc converter design. The optional diode blocks the adapter voltage from
reverse biasing the input, and allows a PoE source to apply power provided that the PSE output voltage is
greater than the adapter voltage. The penalty of the diode is an additional power loss when running from PSE
power. The PSE may not be able to detect and start powering without the diode. This means that the adapter
may continue to power the PD until removed. Auxiliary voltage sources can be selected to be above or below the
PoE operational voltage range. If automatic PoE precedence is desired when using the low-voltage auxiliary
source option, make sure that the TPS2375 inrush program limit is set higher than the maximum converter input
current at its lowest operating voltage. It is difficult to use PG with the low-voltage auxiliary source because the
converter must operate during a condition when the TPS2375 would normally disable it. Circuits may be
designed to force operation from one source or the other depending on the desired operation and the auxiliary
source voltage chosen. However, they are not recommended because they increase complexity and thus cost.
Option 3 inserts the power before the TPS2375. It is necessary for the adapter to meet the TPS2375 UVLO
turnon requirement and to limit the maximum voltage to 57 V. This option provides a valid power-good signal and
simplifies power priority issues. The disadvantage of this method is that it is the most likely to cause transient
voltage problems. Plugging a powered adapter in applies a step input voltage to a node that has little
capacitance to control the dv/dt and voltage ringing. If the wall mount supply applies power to the PD before the
PSE, it prevents the PSE from detecting the PD. If the PSE is already powering the PD when the auxiliary source
is plugged in, priority is given to the higher supply voltage.
ESD
The TPS2375 has been tested using the surge of EN61000-4-2 in an evaluation module (EVM) using the circuit
in Figure 1. The levels used were 8-kV contact discharge and 15-kV air discharge. Surges were applied between
the RJ-45 and the dc EVM outputs, and between an auxiliary power input jack and the dc outputs. No failures
were observed.
ESD requirements for a unit that incorporates the TPS2375 have much broader scope and operational
implications than those used in TIs testing. Unit level requirements should not be confused with EVM testing that
only validated the TPS2375.
EXTERNAL COMPONENTS
Transformer
Nodes on an Ethernet network commonly interface to the outside world via an isolation transformer per IEEE
802.3 requirements, see Figure 1. For powered devices, the isolation transformer must include a center tap on
the media (cable) side. Proper termination is required around the transformer to provide correct impedance
matching and to avoid radiated and conducted emissions. Transformers must be specifically rated to work with
the Ethernet chipset, and the IEEE 802.3af standard.
Input Capacitor
The IEEE 802.3af requires a PD input capacitance between 0.05 F and 0.12 F during detection. This capacitor
should be located directly adjacent to the TPS2375 as shown in Figure 1. A 100-V, 10%, X7R ceramic capacitor
meets the specification over a wide temperature range.
Load Capacitor
The IEEE 802.3af specification requires that the PD maintain a minimum load capacitance of 5 F. It is
permissible to have a much larger load capacitor, and the TPS2375 can charge in excess of 470 F before
thermal issues become a problem. However, if the load capacitor is too large, the PD design may violate IEEE
802.3af requirements.
If the load capacitor is too large, there can be a problem with inadvertent power shutdown by the PSE caused by
failure to meet the MPS. This is caused by having a long input current dropout due to a drop in input voltage with
a large capacitance-to-load ratio. The standard gives Equation 2:
             I          180
               (PD)
       C v
                 10 mA                                                                                         (2)
where C is the bulk capacitance in F and I(PD) is the PD load current in mA.
A particular design may have a tendency to cause ringing at the RTN pin during startup, inadvertent hot-plugs of
the PoE input, or plugging in a wall adapter. It is recommended that a minimum value of 1 F be used at the
output of the TPS2375 if downstream filtering prevents placing the larger bulk capacitor right on the output. When
using ORing option 2, it is recommended that a large capacitor such as a 22 F be placed across the TPS2375
output.
Transient Suppressor
Voltage transients on the TPS2375 can be caused by connecting or disconnecting the PD, or by other
environmental conditions like ESD. The TPS2375 is specified to operate with absolute maximum voltages
V(VDD-VSS) and V(RTN-VSS) of 100 V. A transient voltage suppressor, such as the SMAJ58A, should be installed
after the bridge and across the TPS2375 input as shown in Figure 1. Various configurations of output filters and
the insertion of local power sources across either the TPS2375 input or output have the potential to cause
stresses outside the absolute maximum ratings of the device. Designers should be aware of this possibility and
account for it in their circuit designs. For example, use adequate capacitance across the output to limit the
magnitude of voltage ringing caused by downstream filters. Plugging an external power source across the output
may cause ESD-like events. Some form of protection should be considered based on a study of the specific
waveforms seen in an application circuit.
Layout
The layout of the PoE front end must use good practices for power and EMI/ESD. A basic set of
recommendations include:
 1. The parts placement must be driven by the power flow in a point-to-point manner such as RJ-45  Ethernet
    transformer  diode bridges  TVS and 0.1-F capacitor  TPS2375  output capacitor.
 2. There should not be any crossovers of signals from one part of the flow to another.
 3. All leads should be as short as possible with wide power traces and paired signal and return.
 4. Spacing consistent with safety standards like IEC60950 must be observed between the 48-V input voltage
    rails and between the input and an isolated converter output.
 5. The TPS2375 should be over a local ground plane or fill area referenced to VSS to aid high-speed operation.
 6. Large SMT component pads should be used on power dissipating devices such as the diodes and the
    TPS2375.
Use of added copper on local power and ground to help the PCB spread and dissipate the heat is recommended.
Pin 4 of the TPS2375 has the lowest thermal resistance to the die.
www.ti.com 10-Jun-2014
PACKAGING INFORMATION
       Orderable Device   Status   Package Type Package Pins Package    Eco Plan      Lead/Ball Finish    MSL Peak Temp       Op Temp (C)          Device Marking        Samples
                            (1)                 Drawing        Qty          (2)              (6)                 (3)                                     (4/5)
                                                                        Addendum-Page 1
                                                                                                                                                    PACKAGE OPTION ADDENDUM
www.ti.com 10-Jun-2014
           Orderable Device             Status    Package Type Package Pins Package             Eco Plan         Lead/Ball Finish         MSL Peak Temp         Op Temp (C)                Device Marking         Samples
                                          (1)                  Drawing        Qty                   (2)                  (6)                      (3)                                             (4/5)
(1)
   The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
   Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3)
      MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4)
      There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5)
   Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6)
   Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
                                                                                                Addendum-Page 2
                                                                                                                                                     PACKAGE OPTION ADDENDUM
www.ti.com 10-Jun-2014
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
                                                                                                Addendum-Page 3
                                                                   PACKAGE MATERIALS INFORMATION
www.ti.com 13-Feb-2016
                                                           Pack Materials-Page 1
                                                                PACKAGE MATERIALS INFORMATION
www.ti.com 13-Feb-2016
                                                        Pack Materials-Page 2
                                                                                                            PACKAGE OUTLINE
PW0008A                                                         SCALE 2.800
                                                                                                      TSSOP - 1.2 mm max height
                                                                                                                    SMALL OUTLINE PACKAGE
                                                                                                                             C
                                        6.6                                                                SEATING PLANE
                                            TYP
                                        6.2
           A                                  PIN 1 ID                                                                0.1 C
                                              AREA
                                                                                           6X 0.65
                                                                                8
                  1
          3.1                                                                           2X
          2.9
         NOTE 3                                                                        1.95
                  4
                                                                                5
                                                                                           0.30
                                                                                      8X
                                                                                           0.19
                                          4.5                                                                              1.2 MAX
                      B                                                                     0.1      C A    B
                                          4.3
                                        NOTE 4
                                                                                      (0.15) TYP
                                    SEE DETAIL A
                                                                                      0.25
                                                                               GAGE PLANE
                                                                                                                   0.75                   0.15
                                                                                    0 -8                                                  0.05
                                                                                                                   0.50
                                                                                                                  DETAIL A
                                                                                                                   TYPICAL
4221848/A 02/2015
NOTES:
1. All linear dimensions are in millimeters. Any dimensions in parenthesis are for reference only. Dimensioning and tolerancing
   per ASME Y14.5M.
2. This drawing is subject to change without notice.
3. This dimension does not include mold flash, protrusions, or gate burrs. Mold flash, protrusions, or gate burrs shall not
   exceed 0.15 mm per side.
4. This dimension does not include interlead flash. Interlead flash shall not exceed 0.25 mm per side.
5. Reference JEDEC registration MO-153, variation AA.
                                                                              www.ti.com
                                                                                EXAMPLE BOARD LAYOUT
PW0008A                                                                                 TSSOP - 1.2 mm max height
                                                                                                        SMALL OUTLINE PACKAGE
                                             8X (1.5)
                        8X (0.45)                                SYMM
                                                                                                     (R0.05)
                                         1                                                           TYP
                                                                                                8
SYMM
                            6X (0.65)
                                                                                                5
                                         4
(5.8)
                                                                                                               4221848/A 02/2015
NOTES: (continued)
                                                                www.ti.com
                                                                               EXAMPLE STENCIL DESIGN
PW0008A                                                                                 TSSOP - 1.2 mm max height
                                                                                                         SMALL OUTLINE PACKAGE
                                           8X (1.5)
                                                                 SYMM                                (R0.05) TYP
                         8X (0.45)
                                       1
                                                                                                 8
SYMM
                           6X (0.65)
                                                                                                 5
                                       4
(5.8)
                                                                                                                   4221848/A 02/2015
NOTES: (continued)
8. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate
   design recommendations.
9. Board assembly site may have different recommendations for stencil design.
                                                                 www.ti.com
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