BQ7693003DBT datasheet(23/63 Pages) TI1

23 / 63 page

bq76920, bq76930, bq76940

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SLUSBK2F – OCTOBER 2013 – REVISED NOVEMBER 2015

7.3.1.1.3 16-Bit CC

A 16-bit integrating ADC, commonly referred to as the coulomb counter (CC), provides measurements of

accumulated charge across the current sense resistor. The integration period for this reading is 250 ms.

The CC may be operated in one of two modes: ALWAYS ON and 1-SHOT.

•

In ALWAYS ON mode, the CC runs at 100%, gathering a fresh reading every 250 ms. The conclusion

of each reading sets the CC_READY bit, which toggles the ALERT pin high to inform the

microcontroller that a new reading is available. To enable Always On mode, set [CC_EN] = 1.

•

In 1-SHOT mode, the CC performs a single 250-ms reading, and similarly sets the CC_READY bit

when completed. This mode is intended for non-gauging usages, where the host simply desires to

check the pack current.

To enable a 1-SHOT reading, ensure [CC_EN] = 0 and set [CC_ONESHOT] = 1.

The full scale range of the CC is ± 270 mV, with a max recommended input range of ± 200 mV, thus

yielding an LSB of approximately 8.44 µV.

The following equation shows how to convert the 16-bit CC reading into an analog voltage if no board-

level calibration is performed:

CC Reading (in µV) = [16-bit 2’s Complement Value] × (8.44 µV/LSB)

(3)

16-Bit CC Result

ADC Result in Decimal

CC Reading (in µV)

0x0001

8.44

0x2710

10000

84,400

0x7D00

32000

270,080

0x8300

–32000

–270,080

0xC350

–15536

–131,123.84

0xFFFF

–1

–8.44

7.3.1.1.4 External Thermistor

One (bq76920), two (bq76930), or three (bq76940) 10 k

Ω NTC 103AT thermistors may be measured by

the device. These are measured by applying a factory-trimmed internal 10k pull-up resistance to an

internal regulator value of nominally 3.3 V, the result of which can be read out from the TSx (TS1, TS2,

TS3) registers.

To select thermistor measurement mode, set [TEMP_SEL] = 1.

Thermistor TS1 is connected between TS1 and VSS; TS2 is connected between TS2 and VC5x (bq76930

and bq76940 only); and TS3 is connected between TS3 and VC10x (bq76940 only). These thermistors

may be placed in various areas in the battery pack to measure such things as localized cell temperature,

FET heating, etc.

The thermistor impedance may be calculated using the 14-bit ADC reading in the TS1/TS2/TS3 registers

and 10k internal pull-up resistance as follows:

The following equations show how to use the 14-bit ADC readings in TS1, TS2, and TS3 to determine the

resistance of the external 103AT thermistor:

VTSX = (ADC in Decimal) x 382 µV/LSB

(4)

RTS = (10,000 × VTSX) ÷ (3.3 – VTSX)

(5)

To convert the thermistor resistance into temperature, please refer to the thermistor component

manufacturer’s datasheet.

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