STW4102 datasheet(22/34 Pages) STMICROELECTRONICS

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Battery monitoring

STw4102

22/34

Battery monitoring

8.1

Gas gauge

The gas gauge is designed to monitor the battery capacity. A current sensing resistor

(typically of 30 m

Ω) is needed between the negative terminal of the battery and the ground.

The sensing resistor voltage drop is input to a 13-bit integrating AD converter. When a

conversion cycle is completed, depending on the output sign, the result is forwarded to the

charge or discharge 24-bit accumulator, and the number of conversions is incremented in a

12-bit counter.

One accumulator accumulates current flowing into the battery during charging and the other

accumulates discharge current during system operation. The remaining battery charge is

given by the difference between the charge and discharge accumulators.

Figure 23.

Gas gauge block diagram

The Digital Base Band (DBB) can control, enable and read gas gauge data through I2C

control registers. The DBB can read the value of the most recent conversion in two’s

complement format by reading the CONVDATA registers.

The RD_REQ bit enables the transfer of the charge/discharge accumulators and conversion

counter register. The transfer can take up to eight 32 kHz cycles, therefore a delay of

AD converter

12 bits + sign bit

ICG+

ICG-

From 2’s

to binary

Charge

accumulator

Discharge

accumulator

24 bit max

Charge

registers

Discharge

registers

Conv_data

registers

Conv_number

12 bits Counter

EOC

Control logic

sign

cg_enable

cg_calibration

cg_clock

Control

registers

32kHz

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