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PMBus - UCD9222+UCD7242 no output

Other Parts Discussed in Thread: UCD9222


I have configured UCD9222 and gave an OPERATION command of 01h, 80h to just turn on the IC. The command get ACK but doesn't turn on the rails. Can someone suggest me why this happens ?


Pawan Ghotikar

  • 1. Check PWM to see if there is no pulse at all or there has been pulses and shut down later. They are different scenarios.

    2. A PAGE command should be sent to device prior the OPERATION command.

    3. A rail's On_Off_Config must be configured to OPERATION to be controlled by OPERATION command.

    4. Vin must be above Vin_on threshold.

    5. Read fault status registers to find out if any fault has been generated in the device.

    6. Strongly suggest use Fusion GUI to tune the power rails. It will be much easier than sending PMBus commands.

  • 4. Vin must be above Vin_on threshold

    In this case, I have 12V Vin with voltage divider dropping down the voltage to 1.8V connected to V_INMON.
    So, what does Vin in this case refer to and how much should I set it to?

    Pawan Ghotikar
  • You can set resistor ratio in GUI (0<ratio<1) so that the device can convert sensed voltage to actual Vin. The actual Vin must > Vin _on threshold before you can turn on a rail.