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bq40z60 - Regarding Permanent Fail and Deep Discharge of Lithium Ion cell

Venugopal S
Intellectual 640 points
Other Parts Discussed in Thread: BQ40Z60

Hi, I have a few queries regarding the permanent fail and deep discharge of cell.

1) Suppose the device enters into Permanent fail, how to get out of it if I dont have any communication interface with the IC ? Any automatic reattempt is possible?

2) Consider a situation where the discharge FET's drain to source gets short and load is connected. Won't the battery deep discharge, as there is no other provision to disconnect the load from the battery?

3) Consider situation number 2 happens and the battery got deep discharged. Now I will have to replace my circuitry, to correct the Drain-Source short. Now the battery is at a very low voltage, say less than 2 V. Can I just change the circuit and connect the same battery? Or should I take it out and charge it separately to 2.5V and then connect back to the new circuit ? Or will the battery become altogether useless?

  • 0
    TI__Guru 73830 points
    The FETs will be disabled if a PF occurs and they cannot be enabled, unless the PF is cleared. The SMBus will be required to clear the PF. Li-ion cells will usually get permanently damaged, if they are discharged to 2V.
  • 0 in reply to ThomasCosby
    Prodigy 180 points

    Thanks for your reply. In case of hardware protection circuit failure , at times there could be a chance that Cell voltage can discharge to less than 2v .   In that case while replacing the hardware ,should the cell also needs to be replaced? Or it can be charged by limiting the charge with precharge current or by ant other means like Narrow Voltage charging?

    Venkatramani/Venugopal

  • 0 in reply to Subramaniam Venkatramani
    TI__Guru 73830 points
    You will have to check the specifications for your cell to see whether is will get damaged if discharged to 2V. That is a severe discharge Li-Ion cells. There is a firmware bug with the bq40z60 that affects the pre-charge features. The external pre-charge FET option will not work, but you can still use the pre-charge that uses the CHG FET. The only issue with it is that there is a bug with the high resolution current mode, so charge current accuracy at low settings will be affected.
  • 0 in reply to ThomasCosby
    Prodigy 180 points

    Thanks for your reply.

    We want to use the precharge mode in the final product , which is scheduled in 6 months . Is TI working towards correcting the bug ?

    venkatramani