LM5007 High Voltage (80V) Step Down Switching Regulator

January 2004

LM5007
High Voltage (80V) Step Down Switching Regulator
General Description Features
The LM5007 Step Down Switching Regulator features all of n Integrated 80V, 0.7A N-Channel Buck Switch
the functions needed to implement low cost, efficient, Buck n Internal HV Vcc Regulator
bias regulators. This high voltage regulator contains an 80 V, n No Control Loop Compensation Required
0.7A N-Channel Buck Switch. The device is easy to apply n Ultra-Fast Transient Response
and is provided in the MSOP-8 and the thermally enhanced n On Time Varies Inversely with Line Voltage
LLP-8 packages. The regulator is based on a hysteretic
n Operating Frequency Nearly Constant with Varying Line
control scheme using an on time inversely proportional to
Voltage
VIN. This feature allows the operating frequency to remain
n Adjustable Output Voltage
relatively constant with load and input voltage variations. The
hysteretic control requires no control loop compensation, n Highly Efficient Operation
while providing very fast load transient response. An intelli- n Precision Reference
gent current limit is implemented in the LM5007 with forced n Low Bias Current
off time that is inversely proportional to VOUT. This current n Intelligent Current Limit Protection
limiting scheme reduces load current foldback. Additional n Thermal Shutdown
protection features include: Thermal Shutdown, Vcc under- n External Shutdown Control
voltage lockout, gate drive undervoltage lockout, and Max
Duty Cycle limiter.
Typical Applications
n Non-Isolated Buck Regulator
n Secondary High Voltage Post Regulator
n +42V Automotive Systems

Package
n MSOP - 8
n LLP - 8 (4mm x 4mm)

Connection Diagram

20078302
8-Lead MSOP, LLP

Ordering Information
Order Number Package Type NSC Package Drawing Supplied As
LM5007MM MSOP-8 MUA08A 1000 Units on Tape and Reel
LM5007MMX MSOP-8 MUA08A 3500 Units on Tape and Reel
LM5007SD LLP-8 SDC08A Available Soon
LM5007SDX LLP-8 SDC08A Available Soon

© 2004 National Semiconductor Corporation DS200783 www.national.com

LM5007
Typical Application Circuit and Block Diagram

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 LM5007
Pin Description
PIN NAME DESCRIPTION APPLICATION INFORMATION
1 SW Switching Node Power switching node. Connect to the LC output
filter.
2 BST Boost Boot–strap capacitor input An external capacitor is required between the BST
and the SW pins. A 0.01uF ceramic capacitor is
recommended. An internal diode between Vcc and
BST completes the Buck gate drive bias network.
3 RCL Current Limit OFF time programming pin A resistor between this pin and RTN determines the
Toff = 10-5 / (0.59 + (FB / 7.22 x 10− 6 x RCL)) variation of off time, along with the FB pin voltage,
per cycle while in current limit. The off time is preset
to 17uS if FB =0V and decreases as the FB pin
voltage increases.
4 RTN Circuit Ground
5 FB Feedback Signal from Regulated Output This pin is connected to the inverting input of the
internal regulation comparator. The regulation
threshold is 2.5V.
6 RON On time set pin A resistor between this pin and Vin sets the switch
Ton = 1.42 x 10-10 RON / Vin on time as a function of Vin. The minimum
recommended on time is 300ns at the maximum
input voltage.
7 Vcc Output from the internal high voltage bias If an auxiliary voltage is available to raise the
regulator. VCC is nominally regulated to 7 Volts. voltage on this pin, above the regulation setpoint
(7V), the internal series pass regulator will
shutdown, reducing the IC power dissipation. Do not
exceed 14V. This output provides gate drive power
for the internal Buck switch. An internal diode is
provided between this pin and the BST pin. A local
0.1uF decoupling capacitor is recommended. Series
pass regulator is current limited to 10mA.
8 Vin Input supply voltage Recommended operating range: 9V to 75V

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LM5007
Absolute Maximum Ratings (Note 1) BST to SW 14V
If Military/Aerospace specified devices are required, VCC to GND 14V
please contact the National Semiconductor Sales Office/ All Other Inputs to GND -0.3 to 7V
Distributors for availability and specifications.
Lead Temperature (Soldering 4 sec) 260˚C
VIN to GND 80V Storage Temperature Range -55˚C to +150˚C
BST to GND 94V
SW to GND (Steady State) -1V
Operating Ratings (Note 1)
ESD Rating (Note 5)
Human Body Model 2kV VIN 9V to 75V

Machine Model 200V Junction Temperature −40˚C to + 125˚C

BST to VCC 80V

Electrical Characteristics
Specifications with standard typeface are for TJ = 25˚C, and those with boldface type apply over full Operating Junction
Temperature range. VIN = 48V, unless otherwise stated (Note 3).
Symbol Parameter Conditions Min Typ Max Units
Startup Regulator
VCC Reg VCC Regulator Output 6.6 7 7.4 V
VCC Current Limit (Note 4) 11 mA
VCC Supply
VCC undervoltage Lockout 6.3 V
Voltage (VCC increasing)
VCC Undervoltage Hysteresis 206 mV
VCC UVLO Delay (filter) 3 µs
Operating Current (ICC) Non-Switching, FB = 3V 500 675 µA
Shutdown/Standby Current RON = 0V 100 200 µA
Switch Characteristics
Buck Switch Rds(on) ITEST = 200mA, 0.74 1.34 Ω
VBST −VSW = 6.3V
(Note 6)
Gate Drive UVLO (VBST – Rising 3.4 4.5 5.5 V
VSW)
Gate Drive UVLO Hysteresis 400 mV
Breakdown Voltage TJ = 25˚C 80 V
VIN to Ground TJ = -40˚C to +125˚C 76
Breakdown Voltage TJ = 25˚C 80 V
BST to VCC TJ = -40˚C to +125˚C 76
Current Limit
Current Limit Threshold 535 725 900 mA
Current Limit Response Time Iswitch Overdrive = 0.1A 225 ns
Time to Switch Off
OFF time generator (test 1) FB=0V, RCL = 100K 17 µs
OFF time generator (test 2) FB=2.3V, RCL = 100K 2.65 µs
On Time Generator
TON -1 Vin = 10V 2.15 2.77 3.5 µs
Ron = 200K
TON -2 Vin = 75V 290 390 490 ns
Ron = 200K
Remote Shutdown Threshold Rising 0.45 0.7 1.1 V
Remote Shutdown Hysteresis 40 mV

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 LM5007
Electrical Characteristics (Continued)
Specifications with standard typeface are for TJ = 25˚C, and those with boldface type apply over full Operating Junction
Temperature range. VIN = 48V, unless otherwise stated (Note 3).
Symbol Parameter Conditions Min Typ Max Units
Minimum Off Time
Minimum Off Timer FB = 0V 300 ns
Regulation and OV Comparators
FB Reference Threshold Internal reference 2.445 2.5 2.550 V
Trip point for switch ON
FB Over-Voltage Threshold Trip point for switch OFF 2.875 V
FB Bias Current 100 nA
Thermal Shutdown
Tsd Thermal Shutdown Temp. 165 ˚C
Thermal Shutdown Hysteresis 25 ˚C
Thermal Resistance
θJA Junction to Ambient MUA Package 200 ˚C/W
SDC Package 40 ˚C/W

Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device
is intended to be functional. For guaranteed specifications and test conditions, see the Electrical Characteristics.
Note 2: For detailed information on soldering plastic MSOP and LLP packages, refer to the Packaging Data Book available from National Semiconductor
Corporation.
Note 3: All limits are guaranteed. All electrical characteristics having room temperature limits are tested during production with TA = TJ = 25˚C. All hot and cold limits
are guaranteed by correlating the electrical characteristics to process and temperature variations and applying statistical process control.
Note 4: The VCC output is intended as a self bias for the internal gate drive power and control circuits. Device thermal limitations limit external loading.
Note 5: The human body model is a 100pF capacitor discharge through a 1.5kΩ resistor into each pin. The machine model is a 200pF capacitor discharged directly
into each pin. The machine model ESD compliance level for Pin 5 is 150V. The human body ESD compliance level for Pin 7 and 8 is 1000V.
Note 6: For devices procurred in the LLP-8 package the Rds(on) limits are guaranteed by design characterization data only.

Detailed Operating Description a fixed time pulse determined by the line voltage and a
programming resistor (RON). Following the on period the
The LM5007 Step Down Switching Regulator features all of switch will remain off for at least the minimum off timer period
the functions needed to implement low cost, efficient, Buck of 300ns. If the FB pin voltage is still below the reference
bias regulators. This high voltage regulator contains an 80V, after the 300ns off time, the switch will turn on again for
0.7A N-Channel Buck Switch. The device is easy to apply another on time period. This switching behavior will continue
and is provided in the MSOP-8 and the thermally enhanced until the FB pin voltage reaches the reference voltage level.
LLP-8 packages. The regulator is based on a hysteretic
The LM5007 operates in discontinuous conduction mode at
control scheme using an on time inversely proportional to
light load currents or continuous conduction mode at heavier
Vin. This feature allows the operating frequency to remain
load currents. In discontinuous conduction mode, current
relatively constant with load and input voltage variations. The
through the output inductor starts at zero and ramps up to a
hysteretic control requires no control loop compensation,
peak value during the buck switch on time and then back to
while providing very fast load transient response. An intelli-
zero during the off time. The inductor current remains at zero
gent current limit scheme is implemented in the LM5007 with
until the next on time period starts when FB falls below the
forced off time, after current limit detection, which is in-
internal reference. In discontinuous mode the operating fre-
versely proportional to Vout. This current limiting scheme
quency can be relatively low and will vary with load. There-
reduces load current foldback. Additional protection features
fore at light loads the conversion efficiency is maintained,
include: Thermal Shutdown, Vcc undervoltage lockout, Gate
since the switching losses decrease with the reduction in
drive undervoltage lockout and Max Duty Cycle limiter. The
load current and switching frequency. The approximate dis-
LM5007 can be applied in numerous applications to effi-
continuous mode operating frequency can be calculated as
ciently regulate step down higher voltage inputs. This regu-
follows:
lator is well suited for 48 Volt Telcom and the new 42V
Automotive power bus ranges.

Hysteretic Control Circuit

Overview
The LM5007 is a Buck DC-DC regulator that uses an on time In continuous conduction mode, current flows continuously
control scheme. The on time is programmed by an external through the inductor and never ramps down to zero. In this
resistor and varies inversely with line input voltage (Vin). The mode the operating frequency is greater than the discontinu-
core regulation elements of the LM5007 are the feedback ous mode frequency and remains relatively constant with
comparator and the on time one-shot. The regulator output load and line variations. The approximate continuous mode
voltage is sensed at the feedback pin (FB) and is compared operating frequency can be calculated as follows:
to an internal reference voltage (2.5V). If the FB signal is
below the reference voltage, the buck switch is turned on for

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LM5007
Hysteretic Control Circuit output capacitor, as shown in Figure 1. The series resistor
(R) will degrade the load regulation. Another technique for
Overview (Continued) enhancing the ripple voltage at the FB pin is to place a
capacitor in parallel with the feedback divider resistor R1.
The addition of the capacitor reduces the attenuation of the
ripple voltage from the feedback divider

High Voltage Bias Regulator

The output voltage (Vout) can be programmed by two exter- The LM5007 contains an internal high voltage bias regulator.
nal resistors as shown in Figure 1. The regulation point can The input pin (Vin) can be connected directly to line voltages
be calculated as follows: from 9 to 75 Volts. To avoid supply voltage transients due to
VOUT = 2.5 x (R1 + R2) / R2 long lead inductances on the input pin (Vin Pin 8), it is always
The feedback comparator in hysteretic regulators depend recommended to connect low ESR ceramic chip capacitor
upon the output ripple voltage to switch the output transistor () 0.1µF) between "Vin" pin and "RTN" pin (pin 4), located
on and off at regular intervals. In order for the internal close to LM5007. The regulator is internally current limited to
comparator to respond quickly to changes in output voltage, 10mA. Upon power up, the regulator is enabled and sources
proportional to inductor current, a minimum amount of ca- current into an external capacitor connected to the Vcc pin.
pacitor Equivalent Series Resistance (ESR) is required. A When the voltage on the Vcc pin reaches the regulation point
ripple voltage of 25mV to 50mV is recommended at the of 7V, the controller output is enabled.
feedback pin (FB) for stable operation. In cases where the An external auxiliary supply voltage can be applied to the
intrinsic capacitor ESR is too small, additional series resis- Vcc pin. If the auxiliary voltage is greater than 7 Volts the
tance may be added. internal regulator will essentially shutoff, thus reducing inter-
For applications where lower output voltage ripple is re- nal power dissipation.
quired the load can be connected directly to the low ESR

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FIGURE 1. Low Ripple Output Configuration

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 LM5007
High Voltage Bias Regulator (Continued)

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FIGURE 2. Self Biased Configuration

Over-Voltage Comparator resistor and into the Ron terminal is approximately propor-
tional to Vin and used internally to control the on timer. This
The over-voltage comparator is provided to protect the out- scheme of input voltage feed-forward hysteretic operation
put from overvoltage conditions due to sudden input line achieves nearly constant operational frequency over varying
voltage changes or output loading changes. The over- line and load conditions. The on time equation for the
voltage comparator monitors the FB pin versus an internal LM5007 is :
2.875V reference (OV_REF). If the voltage at FB rises above
Ton = 1.42 x 10-10 x RON / VIN
OV_REF the comparator immediately terminates the buck
switch on time pulse. The RON pin of the LM5007 also provides a shutdown func-
tion which disables the regulator and significantly decreases
quiescent power dissipation. By pulling the RON pin to below
ON Time generator and Shutdown 0.7V logic threshold activates the low power shutdown
The on time of the LM5007 is set inversely proportional to mode. The VIN quiescent current in the shutdown mode is
the input voltage by an external resistor connected between approximately 100µA internal to the LM5007 plus the current
Ron and Vin. The Ron terminal is a low impedance input in the RON resistor.
biased at approximately 1.5V. Thus the current through the

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LM5007
ON Time generator and Shutdown (Continued)

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FIGURE 3. Shutdown Implementation

Current Limit capacitor is charged by VCC through the internal high voltage
diode. A 0.01uF ceramic capacitor connected between the
The LM5007 contains an intelligent current limit off timer BST pin and SW pin is recommended.
intended to reduce the foldback characteristic inherent with
During each cycle when the Buck switch turns off, the SW
fixed off-time over-current protection. If the current in the
pin is approximately 0V. When the SW pin voltage is low, the
Buck switch exceeds 725mA the present cycle on time is
bootstrap capacitor will be charged from Vcc through the
immediately terminated (cycle by cycle current limit). Follow-
internal diode. The minimum off timer, set to 300ns, ensures
ing the termination of the cycle a non-resetable current limit
that there will be a minimum interval every cycle to recharge
off timer is initiated. The duration of the off time is a function
the bootstrap capacitor.
of the external resistor (RCI) and the FB pin voltage. When
the FB pin voltage equals zero, the current limit off time is An external re-circulating diode from the SW pin to ground is
internally preset to 17uS. This condition occurs in short necessary to carry the inductor current after the internal
circuit operation when a maximum amount of off time is Buck switch turns off. This external diode must be of the
required. Ultra-fast or Schottky type to reduce turn-on losses and
current over-shoot. The reverse voltage rating of the re-
In cases of overload (not complete short circuit) the current
circulating diode must be greater than the maximum line
limit off time can be reduced as a function of the output
input voltage.
voltage (measured at the FB pin). Reducing the off time with
smaller overloads reduces the amount of foldback and also
reduces the initial start-up time. The current limit off time for Thermal Protection
a given FB pin voltage and RCI resistor can be calculated by Internal Thermal Shutdown circuitry is provided to protect the
the following equation: integrated circuit in the event the maximum junction tem-
Toff = 10-5 / (0.59 + (VFB / 7.22 x 10-6 x RCL)) perature is exceeded. When thermal protection is activated,
Applications utilizing low resistance inductors and/or a low typically at 165 degrees Celsius, the controller is forced into
voltage drop rectifier may require special evaluation at high a low power reset state, disabling the output driver. This
line, short circuit conditions. In this special case the preset feature is provided to prevent catastrophic failures from ac-
17uS (FB = 0V) off time may be insufficient to balance the cidental device overheating.
inductor volt*time product. Additional inductor resistance,
output resistance or a larger voltage drop rectifier may be
necessary to balance the inductor cycle volt*time product
and limit the short circuit current.

N - Channel Buck Switch and

Driver
The LM5007 integrates an N-Channel Buck switch and as-
sociated floating high voltage gate driver. This gate driver
circuit works in conjunction with an external bootstrap ca-
pacitor and an internal high voltage diode. The bootstrap

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 LM5007
Operational Waveforms Current Limit VFB vs TOFF
RCL = 50k -600k

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LM5007 Operation: VOUT = 10V, VIN = 20V, IOUT = 250mA

CH1: Switch Node, CH2: VOUT (AC), CH4: Inductor Current
FIGURE 4.

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Operational Waveforms
FIGURE 7.

VIN vs TON
RON = 100k, 200k, 300k

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LM5007 Operation: VOUT = 10V, VIN = 75V, IOUT = 250mA

CH1: Switch Node, CH2: VOUT (AC), CH4: Inductor Current
FIGURE 5.

LM5007 10V Output Efficiency

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FIGURE 8.

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FIGURE 6.

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LM5007
10V, 400mA Demo Board Bill of Materials
ITEM PART NUMBER DESCRIPTION VALUE
C1 C4532X7R2A105M CAPACITOR, CER, TDK 1µ, 100V
C2 C4532X7R1E156M CAPACITOR, CER, TDK 15µ, 25V
C3 C1206C104K5RAC CAPACITOR, CER, KEMET 0.1µ, 50V
C4 C1206C103K5RAC CAPACITOR, CER, KEMET 0.01µ, 50V
C5 C3216X7R2A104KT CAPACITOR, CER, TDK 0.1µ, 100V

D1 MURA110T3 DIODE, 100V, ON SEMI

L1 SLF7045T-101MR60-1 BUCK INDUCTOR, TDK 100µH

R1 CRCW12062003F RESISTOR 200K

R2 CRCW12061003F RESISTOR 100K
R3 CRCW12063011F RESISTOR 3.01K
R4 CRCW12061001F RESISTOR 1K
R5 CRCW12061R00F RESISTOR 1

U1 LM5007 REGULATOR, NATIONAL

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 LM5007
Physical Dimensions inches (millimeters) unless otherwise noted

8-Lead MSOP Package

NS Package Number MUA08A

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LM5007 High Voltage (80V) Step Down Switching Regulator
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)

8-Lead LLP Package

NS Package Number SDC08A

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