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TPS22917: battery charging problem (due to reverse current block)

maceti
Prodigy 230 points

Part Number: TPS22917
Other Parts Discussed in Thread: TPL5110, BQ25060, , LM66100, TPS25946

Hi,

I am designing a system that works with a Li-Po battery, has an on-board charger(BQ25060), and consumes nanoamperes(TPS22917L) when the system is in sleep mode(TPL5110). You can see the power block diagram of the system below.

When the USB is plugged in, the battery should be charged.
The system should be able to work from the USB port, sometimes with a battery and sometimes without a battery.

Everything works great here, except for the battery charging part, as you can imagine. And I realized this painfully after I produced the pcb and assembled the board. Disappointed

The reverse current block in TPS22917 prevents charging.

Now what I want to ask here is, what kind of solution would it make sense to proceed with to charge the battery.

If I use a Load Switch without a reverse current block, how much voltage drop or current limitation will there be when the charge voltage passes over the diode of the mosfet inside?

Or would it be better if I put an ideal diode in parallel with the Load Switch(for example LM66100 or MAX40203 ) for battery charging, as in the block diagram below?



Other than these, I'd be happy to hear if you have any other solutions to suggest.

Thanks.

  • 0
    Prodigy 230 points

    Hello again,
    I did some thinking and research.
    I think the design we want to do is not possible with Load Switch due to the Mosfet diode inside the Load Switches.
    In any case, the battery voltage will go more than 0.2V to the charger, and the battery will not be fully charged. am i right?
    Finally I found this IC.
    XC811x (sorry Ti is not your product, if any similar please tell me.)

    This is a controllable ideal diode.
    I think I solve my problem when I use 2 of these ideal diodes as follows.



    If I do it this way with XC8111, is there a problem I might encounter that I can't see? Or if you have any alternative suggestions I'm still open.

    thanks.

  • 0 in reply to maceti
    TI__Genius 16435 points

    Hi Mahmut,

    Yes, load switches are typically only used for power path protection or power distribution and are not specified to provide bi-directional current flow. 

    The TPS25946 has back to back FETs to allow for current flow in both directions. 

    If there are any further questions, I have looped in Kunal Goel who can speak more to the Efuse device if you are interested. 

    Best Regards, 

    Elizabeth 

  • 0 in reply to Elizabeth Higgins
    Prodigy 230 points

    Hi Elizabeth,

    Thanks for the reply. 

    But I need an ultra low power solution.

    TPS25946 has so much quiescent current. 

    What do you think about my second block diagram?

  • 0 in reply to maceti
    TI__Guru* 79151 points

    Hi Mahmut,

    Ideal diode will not offer current limit . Are you fine with that? What protection features you need from device in between battery and charger ?

    Regards

    Kunal Goel

  • 0 in reply to Kunal Goel
    TI__Genius 16435 points

    Hi Mahmut, 

    This thread is going on two weeks without a reply so I am closing/locking it. If there is another update here please make a new thread. 

    Best Regards, 

    Elizabeth