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TPS65217C with NiMH Battery

Charles Eidsness
Prodigy 20 points

Hi,

I would like to use the TPS65217C with 4 NiMH Cells and an external charger and use the Power Path control in the TPS65217C if I can.

I'm thinking that if I connect the NiMH Cells to the BAT pin and leave the Temp Sense pin floating so the internal charger never turns on this could maybe work. The operating voltage for the 4 NiMH cells is 3.5V to 5.5V and the charging voltage would be up to 6.4V. The 6.4V falls out of the operating range of the BAT pin but within the absolute maximum rating. The AC will always be plugged in while charging so the BAT pin technically won't be operating.

Is this okay or will I have to include my own Power Path switch that can handle the higher voltage?

Thanks,

Charles

 

  • 0
    TI__Expert 4525 points

    In order for AC/USB to be used, they must be higher than BAT (i.e. higher than 6.4V in your case).  So, I don't think this scenario would work.

    Please see the datasheet spec for AC/USB detection threshold.

  • 0 in reply to Stephen Nortman
    Prodigy 20 points

    Ah.... hadn't thought of that. What if I drive BAT_SENSE low while charging? Would that force it to use AC? Or is the FET switch within the part configured so that VBAT can never be higher than AC/USB?

    Would another option be to connect my NiMH battery to AC_IN and provide a supply to BAT while charging? Could I then use the AC_EN bit in the POWER PATH CONTROL REGISTER to force it to use the battery even though I have a higher voltage on AC?

    Thanks,

    Charles

  • 0 in reply to Charles Eidsness
    TI__Expert 4525 points

    Hi Charles - I've answered your questions below:

    What if I drive BAT_SENSE low while charging? Would that force it to use AC?
    [SN] No, I believe the AC/USB detection logic is based on the BAT pin, not BAT_SENSE.

    Would another option be to connect my NiMH battery to AC_IN and provide a supply to BAT while charging?
    [SN] AC/USB have over-voltage protection that would not allow this.