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tps65920 VIO at power up a 0.6V ripple above the 1.8V is that normal

Mohsen Khayami
Mastermind 22391 points

All

 My customer is seeing a ripple on the 1.8V VIO as high has 0.6v when his system power's up. It goes away after he boots the OS (Wince). This does not make sense to me but wondering if you guys have seen this or know what can casue this. Is it possible that maybe the internal 3Mhz clock is not stabel yet but if that was the case then the VDD1 adn VDD@ should ahve the same problem? Any thoughts on this. I ahve asked the customer to send us a scope picture when the system power's up. Let me know what else you guys want to see.

Thanks

Regards

Mohsen

  • 0
    TI__Mastermind 22391 points

    All

     My customer find the problem and it is a good one I think, which is interesting how the GPIO152 (on the OMAP) was bring the VIO up to 2.4V.

    We solved the problem by programming the IRQ output of the ethernet chip to an open drain.
    We now have a clean 1.8V supply.

    The IRQ pin was programmed as a push-pull and it was pushing current into the GPIO152 input with the weak internal pull-up.
    This probably created some unwanted current to this input and thus creating this noise on the 1V8 power rail.

    Regards

    Mohsen