MPM82504 feedback resistor value with internal divider

DC-DC Power Converters
1

When the MPM82504 vout decide with PMBus command, and use the internal vout range. I would like to know which value be used at sense feedback.
I tried the 10K and 1K, however the voltage will be a little bit different from the Vout command.

2

Hello @flint ,

Thank you for posting your question at the MPS Technical Forum.

  • What is the expected output voltage for your application?
  • How different it is from the value at Vout_Command?

From the device’s datasheet, there is a step by step process on how to set the output voltage via PMBus and using internal resistors. This can be found on page 51.

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  • Additionally, have you checked that Register 0xD1 (MFR_CTRL_VOUT) is chosen for the appropriate Vref/Vout ratio?

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Regards,
Edgar

3

Hi Edgar,

Thanks for the reply.
We believe that the PMBus configure is ok, output voltage might have 10mV differ. Sorry we are waiting board transition maybe later we can check again.

So the question actually is what is the value suitable for VSNS+ pull up(no divider), original we put 10K, vout obviosly lower, than we try 1K much better (10mV), I think if we can apply 10ohm or 0ohm, the voltage output will be accurate.
I think because the pull up resister caused the sense feeback a divider with internal resisters.

but we are not sure if there’s other problem we don’t know when we put 0ohm on the pull up from vout to vsns+.

4

Hi flint,

Thank you for the clarification.
Yes, it is not recommended to use a pull-up resistor of the same order of magnitude as the feedback resistors as it can drastically affect the accuracy of the feedback voltage (as you observed by using 10k and 1k resistors).
As for a suitable resistor value, any resistor below 100ohms will work fine. For instance, you can certainly use either 10ohm or 0ohm on top of the feedback resistors.

Regards,
Edgar

5

Hi Edgar,
It sounds good.
One more question: in our configuration, we have 3 and 4 MPM82504 devices are working in parallel.
Can we still use the same feedback pull‑up resistor (below 100 Ω)?
By the way, the pull‑down on VSNS‑ is set to 0 Ω.

Thank you

6

Hi Flint,

Yes, you can use the same pull-up resistor for paralleled outputs.

Regards,
Edgar