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Original question:

BQ25792: Trickle charge won't go above ~2V

BQ25792: Trickle charge won't go above ~2V (Continued)

Jim McGarvey
Intellectual 490 points
Part Number: BQ25792
Other Parts Discussed in Thread: BQ28Z610

Following up this earlier conversation with Jeff:

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1023407/bq25792-trickle-charge-won-t-go-above-2v?tisearch=e2e-sitesearch

The workaround we arrived at in that thread works for batteries that are shut down, but does not work if the battery is dead (CUV) and turned off.

In the shut down case, the fuel gauge (BQ28Z610) just needs to briefly see some voltage on the pack terminal to wake up and enable the discharge FET. But if the battery is dead, the fuel gauge will keep the discharge FET off until the battery trickle charges above CUV. The change-to-1S workaround fails in this case because the charger output is a brief spike before VBAT_OVP stops it, so the battery doesn't get any charge and stays off.

In the old thread, Jeff had not received a root cause explanation from design. I'm still interested in the status of that and whether the device will be fixed. And in the meantime, I need to find another workaround to allow charging dead batteries.

Thanks!

  • 0
    TI__Guru**** 166136 points

    Hi Jim,

    We found the root cause.  It was a production trim issue that only seemed to affect some ICs from 2 lots, one of which you have. Unfortunately, there is no consistent way to prevent it from happening from your side. We have fixed it in ICs produced after August 2021. 

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 490 points

    Thanks for the update, Jeff.

    Can you list both bad lot numbers so we can verify production parts are good in the future? I have a bunch on backorder which I would expect to be post-August, but would want to be sure when we get them someday.

    I have a hack to the 1S workaround that appears to address the latest problem with dead batteries..

    - Set 1S mode

    - Set VREG to 4900mV

    - Clear EN_AUTO_IBATDIS to disable OVP discharge

    - Set fuel gauge CUV recovery to 2400mV

    This gets enough voltage to trickle the dead cells up to the CUV recovery level and turn the pack on so it can charge normally.

  • +1 in reply to Jim McGarvey
    TI__Guru**** 166136 points

    Hi Jim,

    The lots are 0AANLZ8 and 0AANLS8.  But again, not all parts show the issue and other lots could be affected.  You could determine the IC's production year and month as explained below:

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 490 points

    Thanks, Jeff!