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TPS22976: Load Switch Leaks Current When Off

Aaron McCartney
Prodigy 10 points
Part Number: TPS22976

I am attempting to use a TPS22976 to achieve power supply sequencing. The TPS22976 seems to be acting more like a leaky valve than an actual switch. It is allowing significant current to flow through, even when it is off. This is causing circuits that are powered by Vout to misbehave. Vin is tied to a 3.3V rail that comes up at the same time Vbias does. I originally had ON1 connected to the output of a voltage monitor and was seeing a similar result. I then disconnected the voltage monitor and used an RC ramp to slowly bring up ON1 as seen in the scope capture below. As you can see, this did not help.

  • 0
    TI__Mastermind 19340 points

    Hi Aaron,

    Welcome to e2e!

    Does this happen on multiple units/boards? What do you have connected to the CT pin - or better yet, can you send a schematic? This is not expected behavior so we'll need to see if this is application-related or if the device may have been damaged.

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    Prodigy 10 points

    Hi Patrick,

    I am seeing this on multiple boards. Also, another team is seeing similar issues on a different board; however, we also use the TPS22976 in a product that is released and it has no issues that I know of. The main difference I have noticed between my design and the design on the released product is that I am only using one channel and they are using both channels. Currently, I have ON2 floating; I will try tying it to ground, but I wouldn't expect that to effect channel one. CT1 is connected to a 1nF capacitor.

    Here is a porting of my schematic. Note that in the scope capture in my initial post, Vbias is connected to a 5V rail, not +3.3VS. PG is connected to an RC ramp.

    Thanks,

    Aaron

  • 0 in reply to Aaron McCartney
    TI__Mastermind 19340 points

    Hi Aaron,

    Thanks for the explanation, during that waveform/earlier testing, was VIN connected to VBIAS. VIN should not be larger than VBIAS, was that violated?

    Also, I'd just like to confirm - is there a voltage source or large capacitance downstream on VOUT? And, what load are you using - are you using an eload in constant current mode?

    Do you know if these devices have been subjected to >6V input, hot shorts, reverse current, etc.? Or is this happening on first time power on?

    Also, do you know anything about the issues the other team is having? Please let me know if you'd prefer to continue this in chat/email for confidentiality.

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    TI__Genius 11705 points

    Looks like there was another path that was back-feeding the output of the switch.  Resolved by keeping those parts off.