TPS54821: Disconnect SW waveform in light load at 1000Mhz

Allen Lu

Part Number: TPS54821

Hi Team:

here attach the customer test summary. can you help to check why the SW will disconnect under 1000Mhz in light load like 0.7A?

tks !

TPS54821 ripple&SW issue.pptx

over 2 years ago

0 Nancy Zhang over 2 years ago

TI__Mastermind 49430 points

Hi Allen,

The root cause is that your 12Vin, 1.04Vout which hits min on time (94-145ns). So device will reduce the switching frequency. You could not set to 1MHz, please set 480kHz.

Thanks,

Nancy

0 Allen Lu over 2 years ago in reply to Nancy Zhang

TI__Intellectual 2470 points

Hi Nancy:

tks for your quick feedback, if i am correct, does it means the on-time as below formula need as least >94ns then base on the sync buck formula , the Ton very close to it ,so cause this issue?

0 Nancy Zhang over 2 years ago in reply to Allen Lu

TI__Mastermind 49430 points

Hi Allen,

Yes, you are right. The on time must great than 145ns due to parts variation. If the on time is below min on time, the device could not support it and the switching frequency will be reduced. At full load the on time is larger than light load due to MOSFET/inductor loss. So it seems working at full load.

Thanks,

Nancy

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TPS54821: Disconnect SW waveform in light load at 1000Mhz