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First time configuring a UCD9240

Edwin Brown
Prodigy 20 points
Other Parts Discussed in Thread: UCD9240

I have a new design using the UCD9240.  I am able to configure the part and read the data back.  My problem is that it does not start on power up.  I am only able to start the rails by issuing the start command via the PMBus programmer.  I have seen a few posts mentioning the use of external controllers to communicate with the UCD9240.  Am I missing something in how the part needs to be configured?

  • 0
    TI__Intellectual 1755 points

    Ed,
    The PMBus Standard says that there should be four ways to start a PMBus compliant device and the UCD92xx devices implement all four:

    1.       Start when the input voltage exceeds the values configured in the VIN_ON command.

    2.       Start when the CTRL pin goes active, which is one of the 4 PMBus signals (Clock, Data, Alert and Ctrl) AND the input voltage is above the VIN_ON threshold.

    3.       Issue an OPERATION command to start or stop regulating AND the input voltage is above VIN_ON.

    4.       Issue an OPERATION command to start or stop regulating AND the input voltage is above VIN_ON AND the CTRL pin is active.

    The part is configured to react to one of these four conditions in the ON_OFF_CONFIG command.  In the Fusion Digital Power Designer program, this is configured on the Vout Config tab of the Configuration page.

     The VIN_ON threshold is set on the Iout, Vin & Temp Config tab.

     

     

  • 0 in reply to Mark Hagen
    Prodigy 20 points

    Thank you for the reply Mark!  Based on your reply, I configured the UCD9240 to "Always Converting".  I was under the impression that any Turn On or Turn Off timing would not be in effect with this option.  I have verified that the Timing parameters I programmed do occur.  The one thing I am not clear on is the start method 2, turning on when the CTRL pin goes active and the input voltage is above the Vin-On threshold.  The rails do not energize with this option even though there is a 1K pull up on the CNTL line.  My thinking is that this would confirm the UCD9240 is working or at least regulating it's internal voltages.  I went back to the "Always Converting" option and the voltages turn on on power up.  Thanks again!

  • 0 in reply to Edwin Brown
    TI__Genius 13700 points

    Could it have been that the Control Pin was set with an active low polarity?

    It can be configured with either a positive or negative active state under the ON/OFF_CONFIG setting. 

  • 0 in reply to Edwin Brown
    TI__Genius 13700 points

    Oh, also, if the active state was defined as high then its possible the signal was being pulled low by the USB-to_GPIO adapter if it was connected to the board, assuming the PMBus_CNTL signal line was routed to the controller from the header.  The default state for the control signal is low which would prevent the controller from actvating any rails using this start-up method.  The control line state can be changed from the Fusion Digital Power Designer GUI, it is found on the Montior page under the Status Register/Lines display on the left side of the screen.