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DS2715Z+
NiMH Battery Pack Charge Controller
AVAILABLE
DESCRIPTION The DS2715 is well suited for cost-sensitive charger
applications where the battery pack is either internal
or external to the application. It has been optimized for
safe and reliable charging of 1 to 10 NiMH cells in
series. The internal gain block can be selected as
either a comparator or transconductance amplifier for
charge current regulation. This makes the DS2715
configurable as a switched DC charger, a linear
current regulator, or a switchmode current source.
The DS2715 pre-conditions severely depleted cells
before entering full charge mode. It terminates full
charge using the dT/dt technique, which requires an
external sensing thermistor. Over-temperature, under-
temperature, and over-voltage detection prevents
charging under unsafe conditions. A user selectable
charge timer allows charge rates from 0.167C to 2C.
FAST-CHARGE, TOPOFF 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 pack is being
discharged.
FEATURES Charges 1 to 10 NiMH Cells FAST-CHARGE at up to a 2C Rate PRECHARGE and TOPOFF Charge Modes Help
Cell Conditioning Load Detection Allows the DS2715 to Enter Low
Power Sleep Mode (Less than 10µA) while the
Cell Pack is Discharged dT/dt Charge Termination Eliminates Cell Charge
Stress Monitors Voltage, Temperature, and Time for
Safety and Secondary Termination Regulates Current through Either Linear Control
or Switch-Mode Control LED Output Displays Charge State Small 16-Pin SO Package
APPLICATIONS Portable DVD Players
Portable Television Sets
Handheld Gaming
Test Equipment
Handheld POS Terminals
PIN CONFIGURATION Table 1. ORDERING INFORMATION + Denotes a lead(Pb)-free/RoHS-compliant package. T&R = Tape and reel.
OPERATIONAL DIAGRAM
PART MARKING PIN-PACKAGE DS2715Z+ D2715 16 SO
DS2715Z+T&R D2715 16 SO
DS2715BZ+ D2715B 16 SO
DS2715BZ+T&R D2715B 16 SO
DS2715NiMH Battery Pack Charge Controller
See Table 1 for Ordering Information.
16 SO CBIAS
VCH
VSS
LED1
DNC
VSS
CTG
CTG
VBATT
THM
RT
VDD
SNS-
SNS+
DIV
MODE
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/JEDEC J-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 = 0C to +70C.)
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 = 0C to +70C, unless otherwise noted.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Linear Mode, VDD = 16.5V 1.3 1.6 mA Operating Current
(Note 2) IDDA Comparator Mode,
VDD = 16.5V 150 250 μA
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,
LED1 ILKG Pin Inactive or Device Idle -1 +1 μA
THM Pin Leakage
Current ILKG-THM -1 +1 μA
VBATT Pin Leakage
Current ILKG-Vbatt -50 +50 nA
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
DS2715: NiMH Battery Pack Charge Controller
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Current Sense
Comparator Gain GCOMP (Note 7) 10 Ω-1
AC ELECTRICAL CHARACTERISTICS (4.5V VDD 16.5V, TA = 0C to +70C, unless otherwise noted.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS UVLO Debounce Time tUVLO 10 μs
Current Sense
Comparator Propagation
Delay
tCOMP (Note 7) 250 ns
Discharge Detect
Propagation Delay tDD From detection of current
reversal 1 μs
Return To Normal
Function (Op-Amp or
Comparator Mode)
tRNF Time from reset of discharge
latch 1 μs
RT Timing Accuracy tRt (Note 4) -10 +10 %
Internal Clock Accuracy tBASE -10 +10 %
ELECTRICAL CHARACTERISTICS: CHARGING (4.5V VDD 16.5V, TA = 0C to +70C, unless otherwise noted.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS FAST-CHARGE
Comparator Threshold VFC FAST-CHARGE -127 -121 -115 mV
FAST-CHARGE
Comparator Hysteresis VHYS-FC FAST-CHARGE 31 28 25 mV
TOPOFF and
PRECHARGE
Comparator Threshold
VTO TOPOFF and PRECHARGE -38 -33 -28 mV
TOPOFF and
PRECHARGE
Comparator Hysteresis
VHYS-TO TOPOFF and PRECHARGE 10 8 6 mV
Discharge Latch Reset
Threshold VDCHG-RST -15 -10 -5 mV
Discharge Latch Set
Threshold VDCHG-SET Reverse current through
sense resistor 5 10 15 mV
Low Battery Detect
Threshold VLB From presence detect into
PRECHARGE 0.95 1.0 1.05 V
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
Threshold Hysteresis VHYS-PD 90 100 110 mV
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
DS2715: NiMH Battery Pack Charge Controller
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS dT/dt Blanking Time tBLANK 3.85 4.3 4.75 Min
PRECHARGE Timeout tPC-TO 30 Min
FAST-CHARGE Timer
Range tFC 0.5 6 Hours
DS2715 1:2 TOPOFF to FAST-
CHARGE Duration Ratio
DS2715B 1:4
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 Chip Supply Return and Local Ground Reference
4 LED1 Charging Indicator Output DNC Do Not Connect
6 VSS Chip Supply Return and Local Ground Reference CTG Connect to Local Ground (VSS) CTG Connect to Local Ground (VSS)
9 MODE Mode Select. Connect to VSS for linear mode of operation or CBIAS for comparator
mode of operation.
10 DIV Thermistor Divider. Stable output to form a resistor divider for measuring
temperature on THM
11 SNS+ Positive Current Sense. Connect to the charge source 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: +4.5V to +16.5V range
14 RT Failsafe Timeout. Timeout is selected by an external resistor from RT to VSS
15 THM Thermistor Input. Connect to a thermistor located in the cell pack and a divider
resistor from the Div pin
16 VBATT Battery Voltage Sense Input. Connect to a divider from the positive terminal of the
cell stack to measure the voltage of a single cell
DS2715: NiMH Battery Pack Charge Controller
Figure 1. BLOCK DIAGRAM DS2715: NiMH Battery Pack Charge Controller
Figure 2. STATE DIAGRAM iscarg Ltcht
isc
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la se
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 while the cell pack is
already inserted, or with the detection of cell insertion after power-up.
After cell presence confirmation, PRECHARGE qualification occurs to prevent fast charging of deeply depleted
cells or charging under extreme temperature conditions. Pre-charging is performed at a reduced rate of
approximately ¼ the FAST-CHARGE current until each cell reaches 1V. The algorithm then proceeds to the FAST-
CHARGE phase. Fast charging continues as long as the cell pack temperature is less than 50C based on the
THM voltage, and the cell voltage as measured at the VBATT pin in the middle of the resistor divider remains below
1.65V, indicating the cell pack is still present. Fast charging terminates normally 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 TOPOFF. The DS2715 has an internal charge timer as secondary overcharge protection if the charge is not
terminated properly 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.
Following a normally terminated or timed-out FAST-CHARGE phase, the DS2715 enters TOPOFF. It remains in
this state for one-half (one-quarter for DS2715B) of the period of the FAST-CHARGE timeout as selected by the
external resistor on RT. After the TOPOFF charge timer expires, the DONE phase continues indefinitely until the
cell pack is removed from the charger or DISCHARGE mode is entered. For the standard application circuit
configuration, when a load drawing at least Vdchg-set across the sense resistor is 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. Throughout the charging process, the open-drain LED1 output indicates 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 10s deglitch circuit provides noise
immunity. Once VDD reaches an acceptable operating voltage, the DS2715 enters the PRESENCE state.
DS2715: NiMH Battery Pack Charge Controller
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 when used with recommended thermistor and
resistor values). If both of 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 PRECHARGE state when a valid cell voltage is applied to VBATT and the cell temperature
as measured by the DS2715 thermistor circuit is within the valid charging range. PRE-CHARGE mode has a 4
second filter to suppress noise on VBATT caused by cell insertion that may cause a premature return to PRESENCE
state. The DS2715 precharges 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. The polarity of the voltage drop across the sense
resistor is referenced to the polarity relationship indicated by the SNS+ and SNS- pins on the device. Precharging
will last until the cell voltage measured by VBATT exceeds 1.0V (VBATT > VLB), at which time the DS2715 will enter
the 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 PRECHARGE, the DS2715 enters the FAULT state. If at any time during
PRECHARGE 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 about -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 TOPOFF 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 TOPOFF 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 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.
TOPOFF In TOPOFF 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 (one-quarter for DS2715B) 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
regulated charging of the cell pack and LED is driven high-impedance to indicate no charging is taking place. A
maintenance charge can be applied to the cells by providing a one-way resistive path from the charge source to the
cell pack bypassing the regulating transistor. See the example in the circuit of Figure 3. The DS2715 remains in the
DONE state until a cell voltage greater than 1.65V (VOPEN) is detected on VBATT indicating cell pack removal, the Rt
pin is floated (see SUSPEND function), or DISCHARGE mode is entered.
FAULT The DS2715 enters FAULT if PRECHARGE is unable to charge the cell above 1.0V (VLB) before the 30 minute
PRECHARGE timeout (tPC-TO) or if the cell temperature exceeds 50°C during PRECHARGE. In the fault state, VCH
is high impedance and LED1 output pulses 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.
DS2715: NiMH Battery Pack Charge Controller
Suspension of charge activity is possible by floating the RT pin. The state machine and all timers are reset to their
presence test conditions when suspending from a charge mode. The DISCHARGE mode is not affected by the
SUSPEND function. The Vch output is high-impedance for charging modes, and operates as normal for
DISCHARGE mode during SUSPEND. The SUSPEND function is useful for resetting the DS2715 in applications
where the batteries are not removed from the circuit and DISCHARGE mode is not utilized. It also allows for a
means to stop charging by the application circuit, such as with a microcontroller signal for example.
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. Initially, the discharge current must flow
through the parasitic diode of the PFET regulating transistor until the DS2715 switches to DISCHARGE mode.
While in this mode, voltage sensing, thermal sensing, and the LED1 output are disabled. The VCH pin is driven low
to fully bias the charge control transistor into a low impedance state and allow the pack to be discharged. Current
drain of the DS2715 drops to IDDD. The DS2715 remains in DISCHARGE mode until a charge current across the
sense resistor causes a sense voltage of at least VDCHG-RST or the device is power cycled. When either of these
events occur, the DS2715 enters the PRESENCE state to begin a new charge cycle.
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 2
summarizes the LED operation for each charge condition.
Table 2. LED DISPLAY PATTERNS BASED ON CHARGE STATE CHARGE STATE NO BATTERY CHARGING DONE FAULT DISCHARGE MODE
LED1 High-Z Blinks at 1HZ,
50% duty cycle High-Z Blinks at 4Hz,
50% duty cycle High-Z High-Z = High Impedance
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 VCH
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. PMOS is the preferred device type when the pass element will also be
used as a discharge path to the load. This is because sufficient transconductance with both polarities of drain
current is easily realized compared to the difficulty in achieving this with BJT types. The SNS- pin is a remote-
sense return and should be connected to the battery ground side of the sense resistor using a separate isolated
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 PRECHARGE and TOPOFF, the voltage across the sense resistor is maintained at VTO.
Current-Sense Comparator Mode The comparator in the DS2715 switches the open drain VCH pin between ON and OFF when the sense resistor
