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BQ76952: CC gain calibration-calculation

Mike Stallone
Prodigy 10 points
Part Number: BQ76952
Other Parts Discussed in Thread: BQSTUDIO

Tool/software:

Hello,

I am attempting to calibrate the CCgain on my device to be very sensitive. I have a nominal Rsense of 0.5 mOhms, which gives me an effective ccGain of 15.1368, based on the below equation for CCGain:

This is not sensitive enough, however, and I need to be able to run this calculation in an automated way to calibrate the gain for each board I am working on, since each board will have an Rsense that varies up to +/-10%

From SLUAA32A (BQ769x2 Calibration and OTP Programming Guide), I have the following equation/procedure for calculating ccGain:

When I run this procedure, I get the following values:

Ib = -1000 (1A)

Ia = 0 (0A)

CC_CountsB = -17000

CC_CountsA = 158

Running the above calibration calculation I get ccGain = (-1000-0)/(-17000-158) = 0.0582818

Back-calculating for Rsense = 129.858, which is nowhere near correct. Setting ccGain (and capacity gain) to that value gives me an effective 

What is going wrong here? Am I running the wrong calculation for ccGain? 

  • 0
    Prodigy 10 points

    To expand on the previous, I am receiving the values over I2C using the readCal1 subcommand, and I am writing CCgain and Capacity gain over I2C as well. I am able to calibrate TOS, Pack, and LD sensors no problem using the calibration procedure from the datasheet, but this current calculation is not correct. Also, I am able to run the auto calibration procedure of BQStudio, combined with the EVM2400 to auto-calibrate the current sensor to a correct value (0.512 Rsense in this case), so this suggests that my equation (or cc2 counts?) are the issue, and not the hardware itself

  • 0
    Prodigy 10 points

    I figured it out. From the previously mentioned SLUAA32A:

    The technical reference manual states that CC2Count = bytes 2-5 of the READCAL1 subcommand. However, this is not true. CC2 is only bytes 3-4 of READCAL1 subcommand

    Adjusting for this, I have the following values for calibration:

    IA = 3000 (3A)

    IB = 1000 (1A)

    CC2_CountsA = 65471

    CC2_CountsB = 65333

    This gives CCGain = 14.4928, which yields an RSense of 0.5222 mOhms, which is correct