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Cell Voltage

Calibration of Cell Voltage Monitor Amplifier Gain

bq29312A

SLUS629A – JANUARY 2005 – REVISED AUGUST 2005

FUNCTIONAL DESCRIPTION (continued)

The cell voltage is translated to allow a system host to measure individual series elements of the battery. The

series element voltage is translated to a GND-based voltage equal to 0.15 ±0.002 of the series element voltage.

This provides a range from 0 V to 4.5 V. The translation output is inversely proportional to the input using the

following equation.

Programming CELL_SEL (b1, b0) selects the individual series element. The CELL_SEL (b3, b2) selects the

voltage monitor mode, cell monitor, offset, etc.

The cell voltage monitor amplifier has an offset, and to increase accuracy, this can be calibrated.

There are a couple of methods by calibration circumstance.

The following procedure shows how to measure and calculate the offset and gain as an example.

•

Step 1

– Set CAL1=1, CAL0=1, CELL1=0, CELL0=0, VMEN=1

– VREF=measured reference voltage

•

Step 2

– Set CAL1=0, CAL0=0, CELL1=0, CELL0=1, VMEN=1

– The output voltage includes the offset and represented by:

Where K = CELL Scaling Factor

•

Step 3

– Set CAL1=1, CAL0=0, CELL1=0, CELL0=0, VMEN=1

– Measuring scaled REF voltage through VCELL amplifier.

– The output voltage includes the scale factor error and offset and is represented by:

•

Step 4

•

Step 5

– Calculate the actual offset value where:

•

Step 6

– Calibrated cell voltage is calculated by:

•

Set CAL1=0, CAL0=0, CELL1=0, CELL0=1, VMEN=1

•

Set CAL1=0, CAL0=0, CELL1=1, CELL0=0, VMEN=1

•

Set CAL1=0, CAL0=0, CELL1=1, CELL0=1, VMEN=1

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