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BQ40Z80: bq40z80 cc gain units

Nelson "Buck" Smith
Prodigy 20 points
Part Number: BQ40Z80
Other Parts Discussed in Thread: BQSTUDIO

Tool/software:

The procedure slua868 specifies  cc gain  as  not the milliamps per ADC bit where:

cc_gain =   Cal_current / (cal_adc_average - (cc_offset/cc_offset_samples))



but in BQ Mgmt studio  at 0x4006 I see that current gain and capacity gain  have units of milliohms (presumably the sense resistor), not the milliamps per ADC values specified in slua868.  Which is correct?

  • 0
    TI__Mastermind 31680 points

    Hello,

    This question has been assigned and will be reviewed when possible.

    Thank you,
    Alan

  • 0 in reply to Alan Frias
    TI__Mastermind 29225 points

    Hi Nelson,

    For parameter units, please use what is specified within bqStudio.

    Regards,

    Anthony

  • 0 in reply to Anthony
    Prodigy 20 points

    I am calibrating now by calculating Rsense and writing to to CC Gain at 0x4006  and CC Capacity Gain at 0x400A.  This is an automated calibration / test system, using TI python, dll and progbqfs tools.  When I look at Gains in BQStudio after calibration, CC Gain at 0x4006 shows what I wrote e.g. 1.905 milliohm, but CC Capacity Gain at  0x400A shows a much larger number, very close to 289261.6178 time the calculated Rsense in milliohm.  289261.6178 is a magic number referenced on page 9 of slua868 calibration procedure.  What is going on there?  

    I have also discovered that formulas for pack and bat gain on pages 5 and 6 of slua868 are off by factor of two.  The formulas in the document produce gains that overflow their 16 bit gain registers.  Using 2^15 (32768) instead of 2^16 produces gains which, when written to flash, calibrate to within one part in 10,000 at 20000 millivots.