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TPS274C65: The reason why VDD shall come from the same supply as VS

Ulf Nilsson
Prodigy 20 points
Part Number: TPS274C65

Tool/software:

We didn't see the following in the datasheet until after we did our board.

When the device is configured to support an external regulator connected to VDD, it is required that the supply input for the external regulator is derived from the same VS supply.

What can happen if we don't follow this? 

On our board we can turn on Vs first or VDD first. As long as we don't destroy anything, we will be happy. 

On the next board we will redesign this to follow the datasheet.

  • +1
    TI__Mastermind 34905 points

    Ulf,

    The danger here is that there is a diode path from VDD to VS. If VS was shorted to ground and VDD was supplied, you would have a big voltage drop across this internal diode with the potential to damage.

    To avoid this in your current design, make sure that VS is turned on first, followed by VDD. When turning off, make sure VDD is turned off first and then VS.

    Best Regards,
    Tim