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TPS62177: effects of other power src on input/outpout when TPS62177 is un-powered?

AnBer
Mastermind 28900 points
Part Number: TPS62177

Team,

The use case is:

TPS62177 is powered off as there are no VIN source.
However an other power source provide 3.3V to the TPS62177 SW and VOS pins (see pink arrow on picture below).
I assume that the SW output and VOS input are not fail-safe pins.

-What would be the effect on input and output pins? and are the effect the same on both input/output?
-Does it affect the long term reliability?
-What do you advise in such case  (how to protect INPUT/OUTPUT pins, acceptable period of time that INPUT/OUTPUT pins can see a voltage,..etc)?
-Any existing TI reference design that shows protection for this use case?

Thanks in advance,

A.

  • 0
    TI__Genius 14856 points

    Hello,

    This very specific case depends on your circuitry. Could you share your schematic with us?

    Providing a voltage at the output when no voltage is applied at the input could imply unexpected behaviors. In a buck-converter topology, the high-side MOSFET will conduct via its body diode and charge the input capacitor of your system. If EN pin is linked directly to it, it can also turn on the device.

    With the TPS62177, DCS-control topology is used so the frequency of the system will be adapted regarding the load. If nothing is connected to your input, then the system will not force to increase voltage at the input.

    I assumed this question is related to test procedures, am I correct?

    Thank you very much for reaching out to us!

    Best Regards,
    Dorian 

  • 0 in reply to Dorian Brillet de Cande
    TI__Mastermind 28900 points

    Hi Dorian,

    Thanks for the answer.

    The question is related to reliability and failure over time:

    Can a some of the TPS62177 I/O (SW, VOS,.etc) and internal blocks be damaged  (and how much) over time when the 3.3V voltage is externally applied?
        -For example can the body diode of the high-side MOSFET be damage in this case?

    If there are some risks what do you advise to protect it?

    A.

  • 0 in reply to AnBer
    TI__Genius 14856 points

    Hello,

    To protect your device from unwanted behavior, you can add a diode at the input to prevent current flowing from the output to the input.

    I recommend you read this App Note which details the topic you are facing:

    http://www.ti.com/lit/an/slyt689/slyt689.pdf

    Thank you!

    Best Regards,

    Dorian

  • 0 in reply to Dorian Brillet de Cande
    TI__Genius 14856 points

    Hello,

    I haven't heard back from you. Do you have any further questions on this topic?

    Thank you very much!

    Best Regards,

    Dorian