DS2715

NiMH Battery Pack Charge Controller

www.maxim-ic.com
DESCRIPTION PIN CONFIGURATION
The DS2715 is well suited for cost-sensitive charger
applications where the battery pack is either internal CBIAS VVP2
or external to the application. It has been optimized for CC1 1 16 BATT

safe reliable charging of 1 to 10 NiMH cells in series. VCH

CC2 2 15 THM
VP1
The DS2715 has an internal gain block that can be VSS
LED1 3 14 RTHM2
T
selected as either a comparator or transconductance
LED1
VSS 4 13 VTHM1
DD
amplifier for charge current regulation. The DS2715 is
configurable as a switched DC charger, a linear DNC
LED2 5 12 SNS-
VDD
current regulator, or a switchmode current source. VSS
CSOUT 6 11 SNS+
TMR
The DS2715 pre-conditions severely depleted cells
CTG
VN1 7 10 DIV
CTST
before entering full charge mode. The DS2715
terminates full charge using the dT/dt technique. It CTG
VN0 8 9 MODE
DMSEL
requires an external thermistor for dT/dt detection.
Over-temperature, under-temperature, and over- 16 SO
voltage detection prevents charging under unsafe See Table 1 for Ordering Information.
conditions. A user selectable charge timer allows
charge rates from 0.15C to 2C. Fast-charge, Top-off
and Done modes are included for highly reliable, safe
charging of NiMH cells. Discharge mode allows the
DS2715 to enter a low power sleep state while the cell Table 1. ORDERING INFORMATION
pack is being discharged.
PART MARKING PIN-PACKAGE
DS2715Z+ DS2715+ 16 SO
FEATURES DS2715Z+T&R DS2715+ 16 SO Tape-and-Reel
§ Charges 1 to 10 NiMH Cells + Denotes lead-free package.
§ Fast Charges up to a 2C Rate
§ Pre-Charge and Top-Off Charge Modes Help Cell
Conditioning
§ Load Detection Allows the DS2715 to Enter Low OPERATIONAL DIAGRAM
Power Sleep Mode (Less than 10µA) while the
Cell Pack is Discharged CHARGE
§ dT/dt Charge Termination Eliminates Cell Charge SOURCE/LOAD
Stress
§ Monitors Voltage, Temperature, and Time for Vdd
Vch
Vbatt Divide by n
Safety and Secondary Termination
DS2715
§ Regulates Current through Either Linear Control THM
or Switch-Mode Control
§ LED Output Display Charge State + - n Cells

§ Small 16-Pin SO Package

GROUND
Sense

APPLICATIONS
Portable DVD Players
Portable Television Sets
Handheld Gaming
Test Equipment
Handheld POS Terminals
Note: Some revisions of this device may incorporate deviations from published specifications known as errata. Multiple revisions of any device
may be simultaneously available through various sales channels. For information about device errata, click here: www.maxim-ic.com/errata.

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 DS2715: NiMH Battery Pack Charge Controller
ABSOLUTE MAXIMUM RATINGS*
Voltage on VDD and VCH Pins with Respect to VSS -0.3V to +18V
Voltage on LED1 Pin -0.3V to +18V
Voltage on SNS- -0.3V to +0.3V
Voltage on CBIAS -0.3V to 6V
Voltage on all Other Pins -0.3V to VCbias
Continuous Sink Current VCH and LED1 28mA
Operating Temperature Range -20°C to +85°C
Storage Temperature Range -55°C to +125°C
Soldering Temperature See IPC/JEDECJ-STD-020
Human Body Model (HBM) ESD Limit of VCH Pin 500V
HBM ESD Limit of all Other Pins 2KV
*This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation
sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability.

RECOMMENDED DC OPERATING CONDITIONS

(4.5V £ VDD £ 16.5V; TA = 0°C to +70°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Supply Voltage VDD (Note 1) 4.5 16.5 V
LED1 Voltage VLED (Note 1) 0.0 16.5 V
Mode Voltage VMODE (Note 1) 0.0 VCbias V
VCH Voltage VVCH (Note 1) 0.0 16.5 V

CBIAS Capacitor Range CCbias .02 .15 µF

RT Resistor Range RRt 20 240 KΩ

DC ELECTRICAL CHARACTERISTICS
(4.5V £ VDD £ 16.5V, TA = 0°C to +70°C, unless otherwise noted.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Linear Mode, VDD = 16.5V 1.3 1.6 mA
Operating Current
IDDA Comparator Mode,
(Note 2) 150 250 µA
VDD = 16.5V
Idle Current IDDS VDD < VUVLO 10 µA
Discharge Current IDDD Discharge latch set (Note 2) 200 µA
UVLO Threshold VUVLO VDD Rising (Note 3) 3.8 3.9 4.0 V
UVLO Hysteresis VUVLO-HYS VDD Falling 35 mV
VCH Sink Current IOL-Vch VOL = 1.5V 20 mA

LED1 Sink Current IOL-LED VOL = 1.0V 20 mA

Leakage Current, VCH,
ILKG Pin Inactive or Device Idle -1 +1 µA
LED1
THM Pin Leakage
ILKG-THM -1 +1 µA
Current
VBATT Pin Leakage
ILKG-Vbatt -50 +50 nA
Current
CBIAS Voltage VCbias 0 < ICbias < 0.4mA 3.9 4.0 4.3 V

DIV Pin Load Current IDiv 500 uA

Current Sense Amplifier -1
GERR 100µA < I Vch < 20mA 5 6.25 7.5 Ω
Gain

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 DS2715: NiMH Battery Pack Charge Controller
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Current Sense -1
GCOMP (Note 7) 10 Ω
Comparator Gain

AC ELECTRICAL CHARACTERISTICS
(4.5V £ VDD £ 16.5V, TA = 0°C to +70°C, unless otherwise noted.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
UVLO Debounce Time tUVLO 10 µs
Current Sense
Comparator Propagation tCOMP (Note 7) 250 ns
Delay
Discharge Detect From detection of current
tDD 1 µs
Propagation Delay reversal
Return To Normal
Time from reset of discharge
Function (Op-Amp or tRNF 1 µs
latch
Comparator Mode)
RT Timing Accuracy tRt (Note 4) -10 +10 %

Internal Clock Accuracy tBASE -10 +10 %

ELECTRICAL CHARACTERISTICS: CHARGING

(4.5V £ VDD £ 16.5V, TA = 0°C to +70°C, unless otherwise noted.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Fast Charge Comparator
VFC Fast charge -127 -121 -115 mV
Threshold
Fast Charge Comparator
VHYS-FC Fast charge -31 -28 -25 mV
Hysteresis
Top-off and Pre-Charge
VTO Top-off and pre-charge -38 -33 -28 mV
Comparator Threshold
Top-off and Pre-Charge
VHYS-TO Top-off and pre-charge -10 -8 -6 mV
Comparator Hysteresis
Discharge Latch Reset
VDCHG-RST -15 -10 -5 mV
Threshold
Discharge Latch Set Reverse current through
VDCHG-SET 5 10 15 mV
Threshold sense resistor
Low Battery Detect From presence detect into
VLB 0.95 1.0 1.05 V
Threshold pre-charge
Cell Detect Threshold VDET 1.50 1.55 1.60 V

No Cell Detect Threshold VOPEN 1.60 1.65 1.70 V

Presence Detect
VHYS-PD 90 100 110 mV
Threshold Hysteresis
2.88 2.92 2.96 V
Minimum Charge Temp VTHM-MIN (Note 5, 6)
0 ºC
1.28 1.32 1.36 V
Maximum Charge Temp VTHM-MAX (Note 5, 6)
45 ºC
1.12 1.16 1.20 V
Over Temp VTHM-STOP (Note 5, 6)
50 ºC
dT/dt Detect TTERM 0.425 0.5 0.575 ºC/min

dT/dt Blanking Time tBLANK 3.85 4.3 4.75 Min

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 DS2715: NiMH Battery Pack Charge Controller
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Fast Charge Timer
tFC 0.5 6 Hours
Range
Top-Off to Fast Charge
1:2
Duration Ratio
Note 1: Voltages relative to VSS.
Note 2: Does not include current through VCH, RT, and DIV pins.
Note 3: Below this voltage no I/O pins are active.
Note 4: Does not include tolerance of RT resistor.
Note 5: VBIAS and resistor tolerances must be added to determine actual threshold.
Note 6: Specified temperature thresholds are only valid if recommended thermistor types are used.
Note 7: Specification is guaranteed by design.

DETAILED PIN DESCRIPTION

PIN NAME DESCRIPTION
1 CBIAS Bypass for Internal Voltage Regulator
2 VCH Cell Stack Charge Control Output
3 VSS Ground Reference and Chip Supply Return
4 LED1 Charging Indicator Output
5 DNC Do Not Connect
6 VSS Ground Reference and Chip Supply Return
7 CTG Connect to Ground
8 CTG Connect to Ground
Mode Select. Connect to VSS for linear mode of operation or CBIAS for comparator
9 MODE
mode of operation.
Thermistor Divider. Stable output to form a resistor divider for measuring
10 DIV
temperature on THM
11 SNS+ Positive Current Sense. Connect to the pack side of the sense resistor
12 SNS- Negative Current Sense. Connect to the cell stack side of the sense resistor
13 VDD Chip Supply Input: +4.0V to +5.5V range
14 RT Failsafe Timeout. Timeout is selected by an external resistor from RT to VSS
Thermistor Input. Connect to a thermistor located in the cell pack and a divider
15 THM
resistor from the Div pin
Battery Voltage Sense Input. Connect to a divider from the positive terminal of the
16 VBATT cell stack to measure the voltage of a single cell

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 DS2715: NiMH Battery Pack Charge Controller
Figure 1. BLOCK DIAGRAM

DS2715
Cbias
Pwr
Vbatt
R M
VDD Regulator
HV E U Th

F X
Ref THM
VUVLO UVLO

Disable during
Div discharge
State Machine

Oscillator A
Pre-Charge
Low Cells
D
C
LED1
HV
Fast Charge
Disch. Detect + Ref
Exit on Full
Or Timeout @-0.01V - SNS+

Mode
Pwr 25% Top-Off Charge Ref R
AMP
(Set by Timer) or
Comp - SNS+
Rt start-up test Vsns
-
Ref
+ SNS-
Done, Waiting for event 121mV,
+
Rt to start charging
33mV,
Vch
Charge 10mV
Rt
Timer
RS Latch

VSS
Latch is set until
Vsns negative WRT Vss
VSS

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 DS2715: NiMH Battery Pack Charge Controller
Figure 2. STATE DIAGRAM

DS2715 State Diagram

Discharge
VDD < VUVLO -V UVLO-HYS
Latch Set
(asynchronously from
anywhere)
Reset VDD > VUVLO
Presence
Standby power
Check Rt , set mode TEST
Vch = Hi-Z Vch = Hi-Z
LED1 = Hi-Z LED 1 Hi-Z
Latch Vbatt>1.65
Reset 4 Sec
Delay
t < PCTimeout
PreCHG Vbatt > 1.65V
AND Vref = 0. 033V OR
LED 1 = Charging Vbatt < 1.55V
Discharge Vbatt < 1V 30 min PCtimeout T < 0C
AND

t
OR

se
Mode 0C < T < 45C

ch
T > 45C

la t
Pwr=Low

e
LED1 = Hi-Z

g
Vch = LOW

h ar
isc
t
se

D
tc h

t > PCTimeout
FAULT
La

Discharge OR
rge

Latch T > 50 Vch = Hi-Z

LED 1 = Fault
ha

Still Set? Flash until Vbatt >1. 65

Vbatt>1V
sc
Di

AND
T < PCTimeout
AND
T < 50C
t < Fast Timeout
Fast Overtemp, Overvoltage Detect Vbatt > 1.65
CHARGE
Vref = 0. 121V
LED 1 = Charging

dT/dt OR T > 50
Discharge latch set
t > Fast Timeout
Vbatt > 1.65
or
t < Topoff Timeout Vbatt < 1.0
Topoff T > 50 DONE
CHARGE OR
Vch = Hi-Z
Vref = 0.033V t > Topoff Timeout LED1 = Hi-Z
LED 1 = Charging

Discharge latch set

Vbatt > 1.65

Discharge latch set

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 DS2715: NiMH Battery Pack Charge Controller
DETAILED DESCRIPTION
Charge Cycle Overview
The DS2715 regulates the charge of up to 10 NiMH cells in a series configuration. With the mode select pin the
DS2715 can be configured to regulate either as an error amplifier in linear mode or as a comparator in switched
mode. A charge cycle begins in one of two ways: with the application of power to the DS2715 with cell pack already
inserted or with the detection of cell insertion after power-up.

The charge cycle begins with pre-charge qualification to prevent fast charging of deeply depleted cells or charging
under extreme temperature conditions. Pre-charging is performed at a reduced rate until each cell reaches 1V. The
algorithm proceeds to a fast-charge phase. Fast charging continues as long as the cell pack temperature is less
than 50°C based on the THM voltage, the cell voltage as measured by the VBATT pin remains below 1.65V
indicating the cell pack is still present. Fast charging terminates by measuring the cell pack’s thermal rate of
change dT/dt. When the cell pack’s thermal rate of change exceeds 0.5°C per minute the DS2715 enters top-off.
The DS2715 has an internal charge timer as secondary overcharge protection if the charge is not terminated by the
dT/dt method. The charge termination timer duration is user selectable from 30 minutes up to 6 hours by an
external resistor on the RT pin.

The DS2715 remains in top-off for one-half of the period of the fast charge timer duration as selected by the
external resistor on RT. After the top-off charge timer expires, the done phase continues indefinitely until the cell
pack is removed from the charger or a load is attached. When a load attached to the cell pack, the DS2715
switches to discharge mode. All charge functions are disabled and the regulation FET is driven on to allow the cell
pack to discharge. The LED1 indicator displays the charge status to the user.

Undervoltage Lockout (Reset)

The UVLO circuit serves as a power-up and brownout detector by monitoring VDD to prevent charging until VDD
rises above VUVLO, or when VDD drops below VUVLO - VUVLO-HYS. If UVLO is active, charging is prevented, the state
machine is forced to the RESET state, and all charge timers are reset. A 10ms deglitch circuit provides noise
immunity. Once VDD reaches an acceptable operating voltage the DS2715 enters the PRESENCE state.

Presence
The DS2715 enters the PRESENCE state whenever VDD > VUVLO and VBATT > VOPEN indicating that the charge
source is present, but no cell is available to charge. The DS2715 will remain in the presence state until a cell is
inserted into the circuit causing the voltage on VBATT to fall below 1.55V (VDET) and the cell temperature is inside a
valid charging range between 0°C and 45°C (TTHM-MIN and TTHM-MAX). If both these conditions are met the DS2715
will enter pre-charge. If cells are inserted, but the temperature is outside the valid charging range the DS2715 will
remain in the PRESENCE state until the cell temperature falls within the valid charging range.

Pre-Charge
The DS2715 enters the PRE-CHARGE state when a valid cell voltage is applied to VBATT and the cell temperature
as measured by the DS2715 is within the valid charging range. Pre-charge has a 4 second filter to suppress noise
on VBATT caused by cell insertion. The DS2715 pre-charges the cell by regulating the voltage drop across the sense
resistor to -33mV (VTO) in linear mode or -29mV (VTO - 0.5 x VHYS-TO) in comparator mode. Pre-charge will last until
the cell voltage measured by VBATT exceeds 1.0V (VBATT > VLB) at which time the DS2715 will enter FAST CHARGE
state. If the cell voltage does not exceed VLB within 30 minutes or if the cell temperature exceeds 50°C at any time
during pre-charge, the DS2715 enters the FAULT state. If at any time during pre-charge the voltage on VBATT
exceeds 1.65V (VOPEN), the DS2715 determines that the cell pack has been removed and returns to the
PRESENCE state.

Fast Charge
In fast charge mode, the DS2715 regulates the voltage across the sense resistor to -121mV (VFC) in linear mode or
-107mV (VFC - 0.5 x VHYS-FC) in comparator mode. LED1 indicates the cell pack is being charged. During fast
charge the DS2715 constantly measures the rate of change of the cell temperature (dT/dt). When the cell pack’s
dT/dt exceeds 0.5°C per minute (TTERM) the DS2715 enters the TOP-OFF state. The DS2715 ignores changes in
the cell temperature caused by charge initiation for the first 4.3 minutes (tBLANK). As secondary overcharge
protection, the DS2715 will terminate fast charge and enter top-off based on a time delay set by the external
resistor on the RT pin. This resistor value can set the secondary charge termination delay to anywhere from 30
minutes up to 6 hours. If the cell temperature exceeds 50°C at any time during fast charge, the DS2715 enters the

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 DS2715: NiMH Battery Pack Charge Controller
DONE state. If at any time during fast charge the voltage on VBATT exceeds 1.65V (VOPEN), the DS2715 determines
that the cell pack has been removed and returns to the PRESENCE state.

Top-Off
In top-off mode, the DS2715 regulates the voltage across the sense resistor to -33mV (VTO) in linear mode or -
29mV (VTO - 0.5 x VHYS-TO) in comparator mode. LED1 indicates the cell pack is being charged. The charge timer is
reset and restarted with a time-out period of one half the fast-charge duration. When the charge timer expires or if
the measured temperature exceeds 50°C, the charger enters the DONE state.

DONE/Maintenance
The DS2715 enters the DONE state whenever the charge completes normally or if the measured cell temperature
exceeds 50°C during the charge. While in the done state VCH is driven to high impedance to prevent further
charging of the cell pack and LED1 is driven on to indicate charge completion. A maintenance charge can be
applied to the cells by providing a resistive path from the cell pack to the charge source bypassing the regulator.
See the example circuit in Figure 3. The DS2715 remains in DONE until a cell voltage greater than 1.65V (VOPEN) is
detected on VBATT indicating the cell pack has been removed. The DS2715 then enters the PRESENCE state and
waits for the next cell insertion.

FAULT
The DS2715 enters FAULT if pre-charge is unable to charge the cell above 1.0V (VLB) before the 30 minute pre-
charge timeout of if the cell temperature exceeds 50°C during pre-charge. In the fault state VCH is driven to high
impedance and LED1 blinks to indicate the fault condition. The DS2715 remains in FAULT until a cell voltage
greater than 1.65V (VOPEN) is detected on VBATT indicating the cell pack has been removed. The DS2715 then
enters the PRESENCE state and waits for the next cell insertion.

Discharge Mode
When the DS2715 detects a discharge current voltage drop of VDCHG-SET or greater across the sense resistor,
charging is terminated and the DS2715 enters the DISCHARGE state. While in this mode, voltage sensing, thermal
sensing, and LED1 output is disabled. The VCH pin is driven low to allow the pack to be discharged. Current drain of
the DS2715 drops to IDDD. The DS2715 remains in discharge mode until a charge current of at least VDCHG-RST is
detected. When this occurs the DS2715 enters the presence detect state to begin a new charge cycle.

Application Circuit
Figure 3 shows a typical application circuit for charging a 3-cell stack. The mode pin is tied to VSS for linear
operation. A 75mΩ sense resistor (R10) sets the charge current at 1.6A. The DS2715 regulates the current through
Q1. 68kΩ on RT (R6) sets the fast charge timeout to 102 minutes. R5 and R8 form a 1:3 voltage divider to allow
VBATT to measure the voltage of a single cell. The charge source is isolated with diode CR1 to prevent discharge
through the source connection. R1 and CR2 form a maintenance charge path to supply the cell pack with ~40mA
constant current after the charge completes. Lastly VR1 and R4 create a current leakage path to bias the regulator
circuit and prevent an in-rush current spike when the cell stack is connected to the powered circuit.

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 DS2715: NiMH Battery Pack Charge Controller
Figure 3. TYPICAL APPLICATION CIRCUIT FOR A 3-CELL STACK

LOAD
CR2 100

R1
CR1
+9VDC C1 10 uF Q1
R2 470 IRF9Z24 VR1 5.6V
U1 R4 R5 C2
LED1 R3 1K 200K
DS2715 100 47 uF
LED1 Vch
Vbatt
Vdd
C3 Rt Div R8
10 uF R6 68K 100K
Mode R7
SNS+ 10K
Cbias
VSS THM
VSS CTG SNS-
C4
0.1 uF THM1
R9
R11 10K
47
47

R10 0.075

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 DS2715: NiMH Battery Pack Charge Controller
CURRENT REGULATION
Three basic modes of charging operation are supported by the DS2715: Offline switching through an optocoupler,
linear regulation, and DC input switched mode. The offline switching method requires a voltage clamp on the
regulated output. Mode of operation is selected through the Mode pin. Connecting the Mode pin to VSS configures
the analog block as a transconductance amplifier for linear mode of operation. Connecting the Mode pin to the
Cbias pin configures the DS2715 as a comparator for switched mode of operation.

Current-Sense Amplifier Mode

An error amplifier block provides several options to regulate the charge current. The 20mA open-drain output can
drive a PMOS or PNP pass element for linear regulation, or the output can drive an optocoupler for isolated
feedback to a primary-side PWM controller. The SNS- pin is a remote-sense return and should be connected to the
grounded side of the sense resistor using a separate, insulated conductor. During fast charge, an error signal
between the current-sense signal (across the sense resistor) and the internal reference is produced so the voltage
across the sense resistor is maintained at VFC in a closed-loop circuit. During top-off the voltage across the sense
resistor is maintained at VTO.

Current-Sense Comparator Mode

The comparator in the DS2715 switches between ON and OFF and is capable of driving a PNP bipolar or a PMOS
transistor, enabling the use of a switched-mode power stage. Hysteresis on the comparator input provides noise
rejection. In a closed-loop regulation circuit, the comparator regulates voltage across the sense resistor to a DC
average of:

VRSNS = VFC - 0.5 x VHYS-FC = -0.107V during fast charge

VRSNS = VTO - 0.5 x VHYS-TO = -0.029V during top-off

Charge Rate Selection

The charge rate is determined by an external sense resistor connected between the SNS+ and SNS- pins. The
DS2715 will regulate the charge current to maintain a voltage drop of VFC (VFC - 0.5 x VHYS-FC in comparator mode)
across the sense resistor during fast charge. The sense resistor can therefore be selected by:

Linear Mode: R = VFC / Desired Fast Charge Current

Comparator Mode: R = (VFC - 0.5 x VHYS-FC) / Desired Fast Charge Current

Charge Time and Top-Off Time Selection

Pre-charge has a fixed 30 minute limit generated by an internal oscillator. Charge time and top-off time are
controlled by an external resistor from the RT pin to VSS. Resistors can be selected to support fast-charge time-out
periods of 0.5 to 6 hours and top-off charge time-out periods of 0.25 to 3 hours. If the timer expires in fast-charge,
the timer count is reset and charging proceeds to the top-off charge phase. The top-off time-out period is half of the
fast charge time-out period. If the timer expires in top-off, the DS2715 enters the DONE state. The programmed
charge time approximately follows the equation:

t(minutes) = 1.5 x R(ohms) / 1000

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 DS2715: NiMH Battery Pack Charge Controller
TEMPERATURE SENSE
Accurate temperature sensing is needed to determine end of charge by dT/dt and to detect over temperature fault
conditions. Connecting an external 10kW NTC thermistor between THM and VSS, and a 10kW bias resistor between
Div and THM allows the DS2715 to sense temperature. To sense the temperature of the cell pack, locate the
thermistor close to the body of a cell, preferably in the middle of the cell pack. Several recommended 10kW
thermistors are shown in Table 2.

Min, Max Temperature Compare

The voltage thresholds of the THM input (VTHM-MIN, VTHM-MAX) are set to allow charging to start if 0°C < TCELL < 45°C
when using the recommended 10kW bias and 10kW thermistor. If pre-charging is in progress, and the voltage on
THM reaches VTHM-STOP, pre-charging stops and a fault condition is generated. If the voltage on THM reaches VTHM-
STOP during fast charge or top-off, charging stops and the DS2715 enters the DONE state. Fast charging will
complete normally and top-off will begin if the voltage change on THM exceeds TTERM ºC per minute (dT/dt charge
termination).

Table 2. THM THRESHOLDS

THERMISTOR TEMPERATURE (°C)

THM RATIO
RESISTANCE Fenwal
THRESHOLD OF VCBIAS Semitec
(W) 197-103LAG-A01
103AT-2
173-103LAF-301
MIN 0.73 27.04k 0°C 4°C
MAX 0.33 4.925k 45°C 42°C
STOP 0.29 4.085k 50°C 47°C

Used with a 10k resistor the Semitec 103AT-2 provides about 0.9% full scale per degree sensitivity. This linearity is
shown in the curve in Figure 4. The left axis is the ratio of the sensed voltage to the divider’s input voltage (VCbias).

Figure 4. RATIO OF THM PIN TO CBIAS PIN OVER TEMPERATURE

Divider Output

0.75
0.70
0.65
0.60
Voltage Ratio

0.55
0.50
0.45
0.40
0.35
0.30
0 10 20 30 40 50
Degrees Centigrade

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 DS2715: NiMH Battery Pack Charge Controller
LED1 Output
Open-drain output LED1 pulls low to indicate charge status. When inactive, the output is high impedance. LED1
displays the state of charge and the charge results. The LED1 pin drives low in a 1Hz, 50% duty cycle “blink”
pattern to indicate cells are charging. LED1 blinks at 4Hz, 50% duty cycle to signal a charging fault has occurred.
The LED1 pin remains in a high-impedance state when no cells are present or the discharge latch is set. Table 3
summarizes the LED operation for each charge condition.

Table 3. LED DISPLAY PATTERNS BASED ON CHARGE STATE

CHARGE STATE
NO DISCHARGE
CHARGING DONE FAULT
BATTERY MODE
Blinks at 1HZ, Blinks at 4Hz,
LED1 High-Z High-Z High-Z
50% duty cycle 50% duty cycle

High-Z = High Impedance

Package Information
For the latest package outline information, go to www.maxim-ic.com/DallasPackInfo.

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