• State
  • Locked Locked
  • Replies 1 reply
  • Subscribers 63 subscribers
  • Views 354 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

bq27010 LMD vs. actual capacity

George Mortimer
Expert 1205 points
Other Parts Discussed in Thread: BQ27010

I am having an issue with a battery pack using the bq27010 bqJunior gas gauge chip. The pack is initially programmed with the LMD set to 1736mAh (EEPROM value 0x26).  After the first learning cycle the LMD drops below 1575 (initial - 10%) mAh, even though the actual capacity as monitored by measurement of time and current shows the actual pack capacity as 1800mAh.  After repeated cycling the LMD stays at the 1575 or less value, and the actual measured capacity stays at the 1800mAh value.  The pack is cycled from a fully-charged condition of 4.2V/cell to a fully discharged condition of 2.5V/cell (cutoff of protection device).  Why is the LMD not matching the actual capacity?

  • 0
    TI__Expert 8230 points

    Hello George,

    Could you verify the EDV1 threshold is set correctly? EDV1 should be programmed to a value that dictates there is close to 6.25% of the design capacity remaining before reaching the empty.

    Also, what was the status of the VDQ bit in FLAGS during the discharge? LMD should update to the measured discharge plus 6.25% of the design capacity plus the compensation value due to discharge rate, temperature and age if the VDQ bit is set at the end of the discharge (Voltage <= EDV1).

    The LMD is also restricted to a learn-down maximum of design capacity/8 during any single learning cycle.

    VDQ would clear if the learning cycle is disqualified by any of the following reasons:

    • Cold temperature: Temperature < 0°C when the EDV1 threshold voltage is reached.
    • Light load: A capacity learning cycle is disqualified if average current is less than or equal to 2 times the initial standby load when the EDV1 threshold voltage is reached.
    • Excessive charging: Cumulative Charge > 255 NAC counts (910 µVh) during a learning discharge cycle (alternating discharge/charge/discharge before EDV1 is set).
    • Reset: VDQ is cleared on all resets.
    • Excessive self-discharge: NAC reduction from self-discharge estimate (0.195%) performed 64 times.
    • Self-discharge at termination of learning cycle. If self-discharge estimate causes CAC ≤ DC/16, VDQ is cleared

    Hope this helps.

    Thank you.