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UCD9222 PM_Bus_Cntrl pin pull-up or pulldown?

Slobodan Gataric
Expert 1020 points
Other Parts Discussed in Thread: UCD9222

Hi,

In the UCD9222 datasheet, Table 1  says  to pull pin 20 (PM_Bus_Control) to 3.3V with a 10k ohm resistor. However, in the evaluation board design, it is pull low with 1M ohm resistor. Which one is corect?

Also, I am using it to run 320C6678 multicore DSP. Channel 1 is used to create variable power (0.9V-1.1V controled by VID bits from the DSP) and channel 2 makes fixed 1.0V. Does anybody have a configuration file to achieve this and is willing to share it? I appreciate help very much.

Thnak you.

Gasha Gataric

  • 0
    TI__Genius 13700 points

    The datasheet is a bit ambiguous about the PMBus_CNTRL pin.

    Potentially it is a sequence input to start rail operation, the device is configurable for which rails the pin will act upon and is also configurable as to the Active state of the input.

    This allows the controller to match up with the signal coming from the trigger source without requiring additional circuitry to invert the polarity regardless of its active state.

     Short answer is, both the Table and the schematic are valid solutions, it will just depend on your application's requirements as to how it is implemented.

    If the PMBus_CNTRL pin isn’t defined to control a rail within the configuration then it could be left floating but tying it off to the not valid state is the best practice.

     

    I’ll see about updating the DS to make this clearer than it is currently.

  • 0 in reply to Brad
    Expert 1020 points

    I did not understand the function of the PMBus_Cntrl pin.  Are you saying that the only function it has is to turn on/off rails? If we configure the UDC9222 to turn on automatically (Page 18, ON_OFF_CONFIG) , then it does not matter if we have pull up or pull down. Is this correct understanding?

    Thank you.

    Gasha

  • 0 in reply to Slobodan Gataric
    TI__Genius 13700 points

    Rail turn is controlled by the ON_OFF_CONFIG command which has four selections, Always_Converting, Control pin, Operation command or the combination of Control pin and Operation command.  If you select either Always_Converting or Operation command then the Control pin has no affect on rail turn on.

    However, It is best to tie the PMBus_CNTRL pin to a defined state, a resistor to ground is probably the easiest.