TPS54531: output droop at power-up

CHEN YAN

Part Number: TPS54531

Hi, expert,

My customer found an issue of output droop when powering up using TPS54531, could you please help analysis? Thanks.

The schematic is as below, the input voltage is 24V, output voltage is 12V.(+12V Power and +12V COMM），and +12V COMM is for MCU power supply and 5V auxiliary power supply. +12V Power following additional capacitors.

CH 1：+12V Power CH2:+12V COMM CH3：Total output current

Below is using 10nF Css capacitor

Below is using 100nf//100nf Css capacitor

Below is using 100nf//100nf//100nf Css capacitor

And as the datasheet described, the capacitor of Css should not larger than 27nF, so is it possible to use 100nF//100nF?

Best Regards.

Chen

over 3 years ago

0 Ryan Hu (BSR-MV) over 3 years ago

TI__Expert 4035 points

Hi Chen,

I suggest you change the schematic following the WEBENCH model of TPS54531. You need choose the appropriated inductance and compensation, set the VIN start and stop voltage higher than the target output voltage by configuring the EN resistor network.

0 CHEN YAN over 3 years ago in reply to Ryan Hu (BSR-MV)

TI__Intellectual 1430 points

Hi, Ryan

Could you please be more specific? Which part in their schematic is not right? How can we change that component? Thanks.

Best Regards,

Chen

0 Ryan Hu (BSR-MV) over 3 years ago in reply to CHEN YAN

TI__Expert 4035 points

Hi Chen,

1. You said the input voltage is 24V, then i suggest you to set the VIN start and stop votlage higher than the target output voltage by configuring the R16 and R19. Use the equation 1 and 2 of the datasheet.

2. The inductor value is too high. I suggest to select the inductor value and do the compensation per the WEBENCH model, you can get the link from my previous answer.

Is it clear?

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TPS54531: output droop at power-up