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TPS2115A IN1 to IN2 switching question

David Koerner
Prodigy 40 points
Other Parts Discussed in Thread: TPS2115A

I'm working on a prototype that uses the TPS2115A to control power switching between two sources.  It is definitely functional, but not quite working as I expected.  It seems to 'lean' towards IN2 over IN1 when the voltages are identical, or nearly so, or even in some cases, when IN2 is LESS than IN1.

D1 is connected to ground, D0 is controlled by a micro, but for the above issue, always held high.

Under load, IN1 measures 4.89VDC, IN2 4.86VDC.  I would have expected that IN1 would always be the source in this case, but the TPS2115A is generally using IN2 for the source, and at some times, actually switching between IN1 and IN2 randomly.  I realize this is not much of a difference in voltage.

Can anyone tell me a) why does IN2 seem to have priority over IN1, and b) what voltage differential is required before one is considered 'higher' than the other.   For now, I've modified my prototype to switch the IN1 and IN2 inputs, but I really would  like to understand why this seems to be an issue.

Any thoughts?

  • 0
    TI__Expert 5815 points

    Hello David,

    One suggestion would be to make sure the difference between the two inputs are .2 V to account for hystersis of the comparator.   This would be referenced on page 5 of the datasheet. 

    Regards,

    S.

  • 0 in reply to iConduct
    Prodigy 40 points

    That's the fast response - exactly what I was looking for - just missed it in the data sheet.  I want to say that I appreciate the response, and also pointing out where I could have found the answer (had I looked more closely!).

    This level of support is why I try to use TI parts whenever possible!