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AM335X VDD_MPU_MON pin functionality

Sandeep N S
Intellectual 280 points

Hi,

What is the functionality od VDD_MPU_MON pin?

How it is doing correction in voltages when any voltage difference occures???

Thanks and Regards

Sandeep

  • 0
    TI__Guru**** 393215 points

    Hi Sandeep,

    Please read section 6.1.3 from the AM335X Datasheet Rev. G. This pin is used if you want to provide feedback to the PMIC directly from the AM335X VDD_MPU internal plane. This would negate voltage drops over the external VDD_MPU rail. If a good solid VDD_MPU power plane is designed on the PCB this connection is usually not necessary and VDD_MPU_MON can be directly tied to VDD_MPU.

  • 0 in reply to Biser Gatchev-XID
    TI__Guru 62945 points
    Before using the AM335x VDD_MON terminal, you need to confirm the power supply being used allows a remote sense that originates at the load. Many power sources are only stable when the feedback path is located near the power supply output. These power supplies may not provide a stable ouptut when using a remote sense like the one provided by the AM335x VDD_MON terminal.

    Regards,
    Paul
  • 0 in reply to peaves
    Intellectual 905 points

    Reviving this old thread with a quick follow up question.

    I see that the slvu551 (Powering the AM335x with the TPS65217x) does not use VDD_MPU_MON, though the TPS65271C does have a reference input.  

    On my board, I have measured a 0.2v drop across the VDD_MPU trace [12mil trace, 2500 mil long] - I will increase the trace thickness, however it is advisable to connect VDD_MPU_MON to the pmic's VDCDC2 input also, or is it best just to use a plane or very large trace?

  • 0 in reply to Geoffrey Lansberry
    TI__Guru**** 393215 points
    Hi Geoffrey,

    12mils trace width for VDD_MPU is absolutely inadequate. Please check Table 5-10 from the AM335X Datasheet Rev. I. Keep in mind that there are current surges/fluctuations on this rail. At this distance (2500mils) it's best to design VDD_MPU as a plane.
  • 0 in reply to Biser Gatchev-XID
    Intellectual 905 points
    Thanks, we already plan to fix the trace width, but will have trouble going all the way to a plane. What is you opinion on using the VDD_MPU_MON output from the am335x to the TPS65217C pmic feedback pin to help compensate? Will the PMIC be able to remain stable?
  • 0 in reply to Geoffrey Lansberry
    TI__Guru 62945 points

    Increasing cross sectional area of the power conductor is the best solution.

    The VDD_MPU_MON terminal was added as a way to provide a remote feedback to the power source. However, we found the PMIC output was not stable when VDD_MPU_MON was connected to the PMIC feedback input. This instability occurs because the PMICs were designed with an expectation that the feedback input would be connected directly to their output capacitor.

    Regards,
    Paul