BQ76PL536APAPR datasheet(18/74 Pages) TI1

18 / 74 page

bq76PL536A

SLUSAD3B – JUNE 2011 – REVISED JANUARY 2016

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Feature Description (continued)

7.3.1.3 Cell Voltage Measurements

Use the following formula (all values are in decimal) to convert the returned cell measurement value to a dc

voltage (in mV).

mV = (REGMSB × 256 + REGLSB) × 6250 / 16383

(1)

Example:

Cell_1 == 3.35 V (3350 mV);

After conversion, REG_03 == 0x22; REG_04 == 0x4d

0x22 × 0x100 + 0x4d = 0x224d (8781.)

8781 × 6250 / 16,383 = 3349.89 mV

≈ 3.35 V

7.3.1.4 GPAI or VBAT Measurements

The bq76PL536A features a differential input to the ADC from two external pins, GPAI+ and GPAI–. The ADC

GPAI result register can be configured (via the FUNCTION_CONFIG[GPAI_SRC] to provide a measurement of

the voltage on these two pins, or of the brick voltage present between the BATx pins and VC0.

In the bq76PL536A device, the VBAT measurement is taken from the BATx pin to the VC0 pin, and is a separate

input to the ADC mux. Because this is a separate input to the ADC, certain common system faults, such as a

broken cell wire, can be easily detected using the bq76PL536A and simple firmware techniques.

The GPAI measurement can be configured to use one of two references via FUNCTION_CONFIG[GPAI_REF].

Either the internal bandgap (VREF) or REG50 can be selected. When REG50 is selected, the ADC returns a ratio

of the voltage at the inputs and REG50, removing the need for compensation of the REG50 voltage accuracy or

drift when used as a source to excite the sensor. When the device is configured to measure VBAT

(FUNCTION_CONFIG[GPAI_SRC]

1),

the

device

selects

VREF

automatically

and

ignores

the

FUNCTION_CONFIG[GPAI_REF] setting.

7.3.1.4.1

Converting GPAI Result to Voltage

To convert the returned GPAI measurement value to a voltage using the internal band-gap reference

(FUNCTION_CONFIG[GPAI_REF] = 1), the following formula is used.

mV = (REGMSB × 256 + REGLSB) × 2500 / 16,383

•

FUNCTION_CONFIG = 0100 xxxxb

(2)

Example:

The voltage connected to the GPAI inputs == 1.25 V;

After conversion, REG_01 == 0x20; REG_02 == 0x00

0x20 × 0x100 + 0x00 = 0x2000 (8192.)

8192 × 2500 / 16,383 = 1250 mV

7.3.1.4.2

Converting VBAT Result to Voltage

To convert the returned VBAT measurement value to a voltage, the following formula is used.

V = (REGMSB × 256 + REGLSB) × 33.333 / 2

14 (33.333 ≈ 6.25 / 0.1875)

•

FUNCTION_CONFIG = 0101 xxxxb

(3)

Example:

The sum of the series cells connected to VC6–VC0 == 20.295 V;

After conversion, REG_01 == 0x26; REG_02 == 0xf7

0x26 × 0x100 + 0xf7 = 0x26f7 (9975.)

9975 × 33.333 / 16,383 = 20.295 V

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