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TPS2115A IN1 to IN2 long switch-over time

Ryan Truer
Intellectual 540 points
Other Parts Discussed in Thread: TPS2115A

I am using the TPS2115A to handle a main 4.5V input from a wall-wart (connected to IN1) and 3 AA batteries as a backup (connected to IN2).  I have D0 shorted to ground and D1 connected to IN1 along with a pull-down to ground so that when IN1 is removed it is pulled to ground.  

I have about 100mA of load on the output and when I remove IN1, the part takes a long time (about 27 ms) to switch to IN2.  This should be only a few ms from my understanding.   

I have attached a portion of my schematic along with a plot of the signals.  Yel = IN1, Blu = IN2, Purple = OUT, Green = 3.0V regulator output connected to OUT.

Please let me know where I am going wrong?

Thanks,

Ryan

  • 0
    TI__Mastermind 42795 points

    Hi Ryan,

    First, I want to apologize for the delayed response to your post. For your issue, I am suspicious of the D1 logic voltage level during switchover. IN1/D1 is within the "grey area" around 2V and I'll bet the TPS2115A did not get a clear signal to switch over to IN2.

    Can you retry the test in a manner which pulls D1 below the VIL max threshold of 0.7V?

  • 0 in reply to Eric Wright
    Intellectual 540 points

    Eric,

    I agree that it is in the grey area, for my application and circuit, do you recommend removeing the connection between IN1(pin8) and D1(pin3)?

    Ryan

  • 0 in reply to Ryan Truer
    TI__Mastermind 42795 points

    Since there is an internal pull up on D1, leaving it open will always select IN1. I believe that what you want to do is transition D1 fully from high to low as IN1 falls below some voltage. You might consider adding an SVS to monitor IN1 and when it droops to a chosen level then quickly change D1 from high to low so that IN2 is selected.