Unexpected ramp at MPM54524 pmic

DC-DC Power Converters
1

Hi,
I am using 2 MPM54524 pmic to power the AMD XCZU3EG-1SBV484I.

som_board_schematics
som_board_schematics1458×877 99.1 KB

The order to turn on the IC is in 0V85_1, 0V85, 3V3, 0V85_2, 1V8, 1V1, 0V9, 1V8_1. But before the 3V3 (2nd output of the 2nd pmic) and 1V8 (3rd output of the 1st pmic) rails get to rise, there is an unexpected ramp from these power rails.

IMG_20260606_194936_601
IMG_20260606_194936_6011920×861 213 KB

In the above photo the green rail(0.85V) should be turned on first and then the blue rail(1.8V) should be started. But, here the blue power rail is started before the green power rail. The delay of 4ms is applied only after the green rail started to raise. After 4ms delay the blue power rail started to rise and then why to have a sudden drop and rise? I cant control the unexpected rise of the blue rail(1.8V). I need the stable voltage rise as per written 2ms soft start in the register.

IMG_20260606_191939_709
IMG_20260606_191939_7091920×861 192 KB

The same is repeated in 3.3V(green rail) and 0.85V(blue rail). The blue should be turned on first and then the green. The delay i written between them is 5ms is applied after the blue rail started to rise and after 5ms the 2nd ramp of the output is started. I can’t control the rise which is started before the blue started to rise

Kindly help me to make these two rails 3V3, 1V8 power outputs as stable rise voltage as written in datasheet

Thanks & Regards,
Santhosh

2

Hi Santhosh,

Thank you for posting on the MPS Technical Forum.

Looking at your schematic, I see EN is tied to VIN through an inductor. I would suggest toggling EN with a separate signal and/or pulling up to VCC instead of VIN. See the schematic in the EVB datasheet for reference.

The EN pin plays a large role in power-up and power-down sequencing. If this signal isn’t stable, there may be issues. I would suggest probing the EN pin as well as the rails you have already provided to get a better picture.

Let me know if/how the behavior changes when EN is toggled differently.

Thanks,

Allison