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Original question:

BQ40Z80: CHGV,CHGC and OC bit details

BQ40Z80: OC:Threshold

David Kearney
Prodigy 30 points
Part Number: BQ40Z80
Other Parts Discussed in Thread: BQ40Z50

Tool/software:

I am confused by the OC Threshold value, is it a value that should be greater than the FCC, or is it added to FCC? In this thread you say the default value should be adequate:

 BQ40Z80: CHGV,CHGC and OC bit details 

My guess is that it is added to FCC (or other related value)

I haven't worked with designing batteries for 10 years, the TRMs are getting fatter.

  • 0
    TI__Mastermind 26395 points

    Hello David,

    This trend has been assigned and will be followed up when possible.

    Thank you,
    Alan 

  • 0 in reply to Alan Frias
    TI__Intellectual 1010 points

    Hello David,

    The OC Threshold should be greater than FCC. OC Threshold is used as a limit to trigger an over-current protection mechanism. When the battery current exceeds the OC Threshold, the protection circuit will intervene to prevent damage to the battery or the device. 

    Thanks,

    Adam

  • 0 in reply to Adam Eschler
    Prodigy 30 points

    After reviewing other TRMs, Forum posts and the bq40z80 TRM again and again I've come to the understanding that the OC Threshold should NOT be higher than the FCC. It's tough to find but the OC:Threshold is compared to the "Internal charge counter" which doesn't start counting until SOC reaches 100%. OC:Threshold is the Overage, not the absolute value.

    This is NOT in your documentation and is REALLY hard to find. 

    Best Regards,

    David

  • 0 in reply to David Kearney
    TI__Intellectual 1010 points

    Hi David,

    The internal charge counter is used for coulomb counting and starts counting during whenever there is a charge or discharge, no matter SOC.

    Overcharge occurs when the internal capacity of the gauge measures a larger capacity than the FCC. Can you show me where you are getting that OC Threshold should be lower than FCC?

    Thanks,

    Adam

  • 0 in reply to Adam Eschler
    Prodigy 30 points

    The Internal Charge Counter is mentioned 2x in the bq40z80 TRM, both in section 3.17. It would be a nice addition to have it explained in the text before the table.

    In this thread:  BQ40Z50-R1: OC Flag & Internal Charge Counter  it is mentioned, although the TI Mastermind calls it the internal accumulator and the internal counter, confusing things. In that thread, Kang says "The internal counter accumulates as soon as RemCap >= FCC" that implies that the OC Threshold is a value above the FCC.

    In this thread,  BQ40Z50: happened OC Alert Wyatt Keller, another TI Mastermind, says "The internal charge counter counts the charge after the SOC is 100%." 

    While both of these are regarding the bq40z50 my best educated guess is that it would apply to the bq40z80, too. 

    Regards,

    David

  • +1 in reply to David Kearney
    TI__Intellectual 1010 points

    Hi David,

    My apologies for the previous response, I must correct myself. Internal charge counter starts counting after remaining capacity is greater than FCC. It starts counting once SOC = 100%. The gauge will trip once Internal charge counter > 0, but the device can remain charging. Once the Internal charge counter hits the OC Threshold, then the Overcharge protection will trip. As stated before, OC Threshold is greater than FCC also stated in the first thread you sent. This is the reason because the OC Threshold is the last protection for the gauge to stop overcharging. You can have remaining capacity above FCC, but not yet hit the OC Threshold, depending on how the gauge is configured.

    This is from the BQ40z80 TRM

    Thanks,

    Adam