MP8771 with 5V Vin and 1.2V Vout

DC-DC Power Converters
1

Hi MPS expert,

I’m validating a MP8771 SMPS design with 5V Vin and 1.2V Vout. I’ve looked into the R (R1, R2, Rt) and C (Cf) parameters chosen around MP8771 in its datasheet and EV board, and suppose these parameters are optimized basing on 12V Vin.

What I’m concerning is: as the input voltage going down to 5V, ΔI is also decreased. I don’t know if the R/C parameters for 12V Vin are suitable for 5V Vin and ΔI changes to maintain MP8771 working normally.

My questiona are as below:
(1) Can I just use the R/C paramters in MP8771 datasheet Figure 10 or those in EV8771-Q-00A (except R2) for my 5V Vin design?
(2) Is it necessary to optimize the R/C parameters for 5V Vin to get better transient and stability/jitter performance?
(3) If the answer for (2) is yes, can you please provide a set of R/C parameters for me, or educated me how to calculate them with some guidance?

Thanks in advance.

2

Hello! Thanks for reaching out to MPS. Responses to your questions are listed below.

  1. Yes, can use existing R/C parameters even for 5V range.
  2. It would be best to use EVB to evaluate at desired conditions to understand performance using current R/C settings and if they suffice.
  3. In terms of calculation, the R/C components used on the EVB typically would work across full input voltage range. However, there may be slight modifications that could be done to improve performance. Suggestion would be to repeat step 2 and vary R/C parameters according to any desired improvement.

Regards,
Christian