DS2715 Dallas Semiconducotr, DS2715 Datasheet - Page 8

• Manufacturer Part Number: DS2715
• Description: NiMH Battery Pack Charge Controller
• Manufacturer: Dallas Semiconducotr

DS2715: NiMH Cell Pack Charge Controller
DONE state. If at any time during fast charge the voltage on V
exceeds 1.65V (V
), the DS2715 determines
BATT
OPEN
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 (V
) in linear mode or -
TO
29mV (V
- 0.5 x V
) in comparator mode. LED1 indicates the cell pack is being charged. The charge timer is
TO
HYS-TO
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 V
is driven to high impedance to prevent further
CH
charging of the cell pack and LED 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 (V
) is
OPEN
detected on V
indicating the cell pack has been removed. The DS2715 then enters the PRESENCE state and
BATT
waits for the next cell insertion.
FAULT
The DS2715 enters FAULT if pre-charge is unable to charge the cell above 1.0V (V
) before the 30 minute pre-
LB
charge timeout of if the cell temperature exceeds 50°C during pre-charge. In the fault state V
is driven to high
CH
impedance and LED2 blinks to indicate the fault condition. The DS2715 remains in FAULT until a cell voltage
greater than 1.65V (V
) is detected on V
indicating the cell pack has been removed. The DS2715 then
BATT
OPEN
enters the PRESENCE state and waits for the next cell insertion.
Discharge Mode
When the DS2715 detects a discharge current voltage drop of V
or greater across the sense resistor,
DCHG-SET
charging is terminated and the DS2715 enters the DISCHARGE state. While in this mode, voltage sensing, thermal
sensing, and LED outputs are disabled. The V
pin is driven low to allow the pack to be discharged. Current drain
CH
of the DS2715 drops to I
. The DS2715 remains in discharge mode until a charge current of at least V
is
DDD
DCHG-RST
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 V
for linear
SS
operation. A 75mΩ sense resistor (R10) sets the charge current at 1.6A. The DS2715 regulates the current through
Q1. 68kΩ on R
(R6) sets the fast charge timeout to 102 minutes. R5 and R8 form a 1:3 voltage divider to allow
T
V
to measure the voltage of a single cell. The charge source is isolated with diode CR1 to prevent discharge
BATT
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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