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Or-ing solution for 2 lithium batteries CR2032

Slava Prokopii
Intellectual 2076 points
Other Parts Discussed in Thread: TPS22916

Hello, team.

I'm looking for an OR-ing device, which can be used to chose the one of two available CR2032 lithium batteries to supply the system.

Functional diagram can be presented like this:

Required algorithm of operation is:

1. Device selects one of the two available batteries (e.g. Vin1), and connects this source to Vout pin until the selected battery became discharged.

During operation Vin1 is connected to Vout even if Vin2 voltage is higher than Vin1 voltage

2. When Vin1 is discharged, device switches the Vout to Vin2 input. and uses Vin2 until this will be discharged.

When Vin2 is discharged devices switches Vout back to Vin1, if Vin1 is present and charged enough.

3. STATUS pin indicates which one of the two inputs is used to supply Vout now.

Leakage currents requirmenets:

Iq for the main supply battery <= 1uA

Iq for the backup battery <= 0.25 uA. 

What the single-chip solution can you recommend for such kind of application?

Thank you in advance.

  • 0
    TI__Genius 10652 points

    Slava, 

    Thanks for your questions. The obvious solution for mulitplexing power sources like you need is a power-mux, but power mux ICs cannot meet your very low IQ target.

    nA-scale quiescent current for the active channel is incredible difficult to achieve in a pmux.

    One solution that could work is our load switch like TPS22916 , which has extremely low active and standby Iq which exceeds your requirements.

    However, the solution i post below does not have sophisticated logic or control of switchover voltage. If you need this level of control, you have to add extra circuit to make it work, such as with ultra low power comparator, resitor divider, etc. Alternate solution is to accept 10s of uA of Iq and 

    So my idea is you can use two different variants to achieve a nA scale Iq muxing.

    You can use TPS22916CN for the VIN1 load switch and TPS22916CL (active low) for the VIN2 load switch.

    VIN1 supply is connceted to ON pin of both. When VIN1 drops out it will turn off VIN1 and turn off VIN2 switch.

    Anyways, even with a bit extra circuit to handle the levels which you want one to switch and other to not switch, such as with a discrete comparator, i would still recommend to look into using TPS22916 family as they are some of our lowest iq load switches which can give you additional headroom if you need to add extra circuits.

    Please let me know if you have any further questions on this or comments, otherwise could you press the green button?

    Best

    Dimitri