BQ7693003DBT datasheet(21/63 Pages) TI1

21 / 63 page

bq76920, bq76930, bq76940

www.ti.com

SLUSBK2F – OCTOBER 2013 – REVISED NOVEMBER 2015

For each contiguous set of five cells (VC1 to VC5, VC6 to VC10), when no cells in that particular set are

being balanced, each cell is measured over a 50-ms decimation window and a complete update is

available every 250 ms. In the bq76930 and bq76940, every set of five cells above the primary five cells is

measured in parallel. The 50-ms decimation greatly assists with removing the aliasing effects present in a

noisy motor environment.

When any cells in a contiguous set of 5 cells are being balanced, those affected cells are measured in a

reduced 12.5-ms decimation period, to allow the cell balancing to function properly without affecting the

integrated OV and UV protections. Since cell balancing is typically only performed during pack charge or

idle periods, the shortened decimation periods should not impact accuracy as the system noise during

these times is greatly reduced. This reduced decimation period is only applied to sets where one of the

cells is being balanced. The following summarizes this for the bq76920–bq76940 devices:

•

VC1 to VC5 measurements are each taken in a 50-ms decimation period when all bits in CELLBAL1

•

VC6 to VC10 measurements are each taken in a 50-ms decimation period when all bits in CELLBAL2

•

VC11 to VC15 measurements are each taken in a 50-ms decimation period when all bits in CELLBAL3

•

Total update interval is 250 ms.

Each differential cell input is factory-trimmed for gain and/or offset, such that the resulting reading via I2C

is always consistent from part-to-part and requires no additional calibration or correction factor application.

The ADC is required to be enabled in order for the integrated OV and UV protections to be operating.

The following shows how to convert the 14-bit ADC reading into an analog voltage. Each device is factory

calibrated, with a GAIN and OFFSET stored into EEPROM.

The ADC transfer function is a linear equation defined as follows:

V(cell) = GAIN x ADC(cell) + OFFSET

(1)

GAIN is stored in units of µV/LSB, while OFFSET is stored in mV units.

Some example cell voltage calculations are provided in the table below. For illustration purposes, the

example uses a hypothetical GAIN of 380 µV/LSB (ADCGAIN<4:0> = 0x0F) and OFFSET of 30 mV

(ADCOFFSET<7:0> = 0x1E).

14-Bit ADC Result

ADC Result in Decimal

GAIN (µV/LSB)

OFFSET (mV)

Cell Voltage (mV)

0x1800

6144

380

2365

0x1F10

7952

380

3052

NOTE

When entering NORMAL mode from SHIP mode, please allow for the following times before

reading out initial cell voltage data:

bq76920: 250 ms

bq76930: 400 ms

bq76940: 800 ms

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Product Folder Links: bq76920 bq76930 bq76940

BQ7693003DBT Datasheet(PDF) 21 Page - Texas Instruments

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