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UCD9248 start-up problem

Lukas Holm
Prodigy 110 points
Other Parts Discussed in Thread: UCD9248, SN74LVC1G3157

When I power on my board, the UCD9248 sometimes refuses to start regulating. I can communicate with the device over PMBus. In the Fusion Digital Power Designer GUI, I can see that POWER_GOOD# is asserted. The GUI also reports a Vin reading of 0.790 V, but Vin is acually at 12V. When I measure on the TMUX outputs on the UCD9248, they are all constantly high. It seems like the device sometimes latches up somehow. Most of the times it works just fine, but sometimes when I power up the borad, I get this strange behaviour.

  • 0
    TI__Genius 13700 points

    If the monitored Vin is below the turn-on setting defined in the project file then the rails will not begin operation.

     

    I'm asuming when it does start normally that the controller reports the correct input voltage, i would verify the signal path to the VIN/IIN pin on the controller doesn't have any bad solder joints..

     

  • 0 in reply to Brad
    Prodigy 110 points

    Hi Brad,

    I can't find anything wrong with VIN/IIN path as such. The problem is that the TMUX-0 output is (constantly) high. That means that my analog switch SN74LVC1G3157 is constantly selecting the IIN signal, and never the VIN signal.

    As I said, this only happens sometimes on start-up. Most of the times it works perfectly fine and the TMUX signals toggles as they should and both VIN and IIN are selected and reported as expected.

    Thanks,
    Lukas