DS2714: Quad Loose Cell NiMH Charger

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CHARGE TIMER

The Charge Timer monitors the duration of charge in Fast and Top-Off charge phases, and is reset at the

Resistors can be selected to support Fast charge time-out periods of 0.5 to 10 hours and Top-off charge time-out

periods of 0.25 to 5 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. When the timer

expires in Top-Off, charging proceeds to the Maintenance phase. The programmed charge time approximately

follows the equation:

t = 1.5 * R / 1000

(time in minutes)

SUSPEND

Suspension of charge activity is possible by floating the TMR pin. All CCx outputs become high-Z and the Charge

Timer stops. The state machine and all timers are reset to their Presence Test conditions.

TEMPERATURE SENSE

Connecting an external 10kΩ NTC thermistor between THM1 or THM2 (THMx) and VSS, and a 10kΩ bias resistor

cells, locate the thermistor close to the body of the battery cell. The THM1 thermistor should be placed between

cells 1 and 2, and THM2 thermistor between cells 3 and 4. Alternatively, the thermistors can sense ambient

temperature by locating them away from the cells. THM1 and THM2 can be tied together to sense temperature

using a single thermistor and bias resistor. The temperature qualification function can be defeated by tying THMx

pins to a single resistor divider supplying a voltage between the Thermistor-Min and Thermistor-Max threshold

voltages.

MIN, MAX TEMPERATURE COMPARE

The voltage thresholds of the THMx inputs (VTHM-MIN, VTHM-MAX) are set to allow Fast charging to start if 0

°C <

°C when using the recommended 10kΩ bias and 10kΩ thermistor. If Fast charging is in progress, and the

°C), Fast charging stops and the maintenance phase begins. In

Pre-charge the device will transition to the Fault state if the voltage on THMx reaches VTHM-STOP.

Table 1. THM1, THM2 Thresholds

TEMPERATURE

THM

THRESHOLD

RATIO

OF VDD

THERMISTOR

RESISTANCE

Semitec

103AT-2

Fenwal

197-103LAG-A01

173-103LAF-301

MIN

0.73

27.04k

0C

4C

MAX

0.33

4.925k

45C

42C

STOP

0.29

4.085k

50C

47C

CELL VOLTAGE MONITORING

precede the Fast charge cycle, and when to transition from Pre-charge to Fast charge. Once Fast charging

while the charge control pin (CC1-4) controlling current to the cell is active (low). When the charge control pin is

measurements for charge termination and cell test purposes.