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PCM5142: Clarification required: VCOM pin in VREF mode

John Doe64
Prodigy 80 points
Part Number: PCM5142

Is it mandatory for the VCOM pin to be tied to GND while the chip is operating in VREF mode? Or can it be left with decoupling capacitor as in VCOM mode? What would be the implication of operating in VREF mode with the decoupling capacitor?

  • 0
    TI__Guru 52683 points
    Hi John,

    I am checking with my design team to see what the risk is to not ground the pin. Are you designing the board for VCOM with VREF as a backup? To clarify, VCOM mode uses an ratio of the AVDD voltage for the output amplitude, while VREF mode uses an internal reference for the amplitude of the output. VCOM mode should be used when the supply voltage may not be greater than the recommended minimum of 3.2V, to prevent output clipping. If you are designing a board to support both modes, you could leave the footprint for the capacitor on the pin, but populate it with a 0 ohm resistor for VREF mode.

    Thanks!
    Paul
  • 0 in reply to Paul_Frost
    Prodigy 80 points

    Hi Paul,

    My objective is to make the board as flexible as possible without having to make any modifications later on. If necessary, I can populate the pad with a 0 ohm resistor instead of a capacitor, but if VREF mode is ok with the capacitor, that would make switching between VCOM and VREF something that can be done all in software.

    Thanks.

  • 0 in reply to John Doe64
    TI__Guru 52683 points
    Hi John,

    My design team informed me that the we recommend that the pin be grounded to prevent any external noise from being injected into the pin. But other than precaution, grounding the pin does not affect the application in VREF mode.

    Thanks,
    Paul
  • 0 in reply to Paul_Frost
    Prodigy 80 points
    Thank you very much.