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BQ25798: SYS line restarts when charge is enabled without battery connected

fraannk
Prodigy 10 points
Part Number: BQ25798
Other Parts Discussed in Thread: BQ25792,

Tool/software:

Hi, 

I'm using the BQ25798 in a design with a 1s battery. I came from the BQ25792, as it restarted when charge was enabled with no battery connected. I was told that the 98 had this issue fixed, but the issue still remains. 

I have an intelligent battery that have a protection mode/shipping mode. To get the battery out of this mode I have to apply a charge. From the battery charger point of view this is applying a charge to a battery that is presumably not there (0V), and when enabling the charge, the SYS line resets. What can I do to circumvent this issue? I've tried circumventing this in firmware by detecting the "idle" voltage on BATP but this is very unstable and varies from board to board. 

I also can't check if it's a BATOVP state, as the entire device resets because of this, but I presume this is the reason. 

Thanks in advance. 

  • +1
    TI__Guru**** 165786 points

    Hi Fraannk,

    BQ25798 still has BATOVP if charge is enabled and no battery is connected.  BQ25792 followed this with 30ms converter turn off, which caused SYS to collapse. BQ25798 does not do that. If you can't disable charge at battery removal with /CE pin or bit and TS fault doesn't start charge at battery removal, then you can add about 200uF to BAT.  This prevents the BATOVP but both chargers will still go in and out of charge termination, restart charge, repeat.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 10 points

    I tried adding 200uF to the BAT line and the converter does not reset on the BQ25798 any longer - it does however still reset on the BQ25792. I will have to either implement the extra capacity, or find a way to only start charging when the battery is installed. Thank you.