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PMP20878: need 20V output

omer nazir
Prodigy 50 points
Part Number: PMP20878

Hi Ti Team,

In my design, I have both poe and usb-c as a power source. I want to take the PMP20878 as a reference for POE side.  PMP20878 output voltage is 24v. It would be nice setting poe output voltage to 20V to match USB voltage.

Is it possible to make slight tunning on PMP20878 to set output voltage to 20V?

Thank you,

Ömer

  • 0
    TI__Expert 6160 points

    Hi Omer,

    This should be possible, I am going to loop in the original designer to make sure.

    Please give a bit.

    Thanks,

    Robert 

  • 0 in reply to Robert Taylor1
    TI__Intellectual 2520 points

    Omer,

    You can set the output to 20V by changing the value of R64 to 6.98k ohms.  The only issue may be the VC_IN bias voltage.  The turns ratio between the output winding and bias winding is 2:1.  The bias voltage VC_IN will be approximately half of the 20V output minus the diode drop across D33/D36, so about 9.0-9.4V.  The maximum VC_IN voltage to turn on the start-up regulator in the TPS2373-4 is 9.0V.  I would also change D33/D36 to schottky diodes to provide more margin on the VC_IN turn-on level.  A BAT46WJ_115 or BAS100CS should give you 0.6-0.8V less voltage drop for a minimum VC_IN voltage of approximately 10V.  These both have a 100V rating and are in the same SOD-323 package.

    Thanks,

    David