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Why bq2084 MaxError become 25% in the host system?

Suren Zhou
Intellectual 385 points

Hi All,

 

1) I have a bq284 (V1.33) battery pack return from host system, MaxError is 25%, but the MaxError is 2% when ship out. Could you please provide some possible for this phenomenon?

2) The bq2084 datasheet mention that "voltage-based corrections are applied to the coulomb counter, MaxError() is set to 25%.", how to understand this point?

 

Thanks & regards,

  • 0
    TI__Genius 10235 points

    The are a couple of ways that MaxError could be set to 25%. 

    First, MaxError increments 1% for every 4 cycle counts without a learning cycle.  A learning cycle involves discharging the battery down to 7% RSOC. The gauge makes an FCC correction here and will set the MaxError back to 2%.  If your application does not allow the battery to discharge down to 7% every once in awhile, then MaxError will increase.

    The second way MaxError can be set to 25% is on a voltage correction, as you stated in point 2).  After a reset or loss of power, the gauge, upon power up, will set the RSOC to 25%, 50%, or 75%, depending on the Voltage. The VOC25, VOC50, and VOC75 thresholds determine what voltage corresponds to each percentage. After a learning cycle (discharging down to 7%), the gauge will learn a new FCC and the MaxError will drop to 2%.

  • 0 in reply to Chase7071949597
    Intellectual 385 points

    Dear Chase,

     

    Thanks for your quickly respond.

     

    Thanks & regards,

    Suren

  • 0 in reply to Suren Zhou
    TI__Intellectual 825 points

    I happened to see a similar case recently. So to add to Chase's reply, there is an additional mechanism to set MaxError. It's in Gauge Configuration (0x29) VCOR bit. If this is enabled, a "midrange capacity correction" can occur when condition permits. See "Midrange Capacity Corrections" section in the datasheet.

  • 0 in reply to SW5307
    Intellectual 385 points

    Hi SW,

     

    Thank you share the information to us.

    If VCOR is enabled and keep the pack in the storehouse (The loss of power only self-discharge), whether the pack will be do voltage correction and midrange capacity correction?

     

    Thanks & regards,

  • 0 in reply to Suren Zhou
    TI__Intellectual 825 points

    I think it will.