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TPS65131: Negative Channel Produces No Output

James Lopresto
Prodigy 10 points
Part Number: TPS65131

I am using the TPS65131 split rail converter to generate +12V and -12V from +5V input. Schematic is shown below and is very similar to that shown in the datasheet. +12V output works fine, but the -12V side reads -0.21V.  VREF checks out at 1.22 V.  FBP measures 1.47V, FBN measures 1.08V.  Voltage at OUTN is a couple millivolts.  I do have the PSN terminal tied high and was wondering if that is what is disabling the negative output.   Is there a minimum current required to enable the output?  The board layout looks good and I have checked all traces. Is there anything in the board layout that would cause the negative side to act like it is turned off

 

  • 0
    TI__Guru 58225 points
    Hello James,

    The schematic looks as expected, although I did not go through the external component calculations.

    The converter seems not to switch at all. Please check out the startup behavior with a scope because I expect that it tries to start and then does stop because of a problem. Dependent on the problem, the IC could be damaged already as well.

    Layout could cause such a problem even if it looks ok. We would need to have a more detailed look on it, especially if the switch node is causing some problems on the CN or FBN pins.
    If layout is the last option that is left, I think it is best that you check out the EVM of this device and try to get very close to this one.

    Best regards,
    Brigitte
  • 0 in reply to Brigitte
    TI__Expert 8010 points
    Hello James,

    Do you have any feedback for us? Could you send us the layout and some scope plots to show the behavior?

    Thank you.
    Best Regards.
    Ilona