UC3525A: Questions about the soft start with UC3525A and UCC28250

gu chenjie

Part Number: UC3525A
Other Parts Discussed in Thread: UCC28250

Hello,

- How does the internal soft start work in UC3525? is soft start on UC3525 different from UCC28250?

-in UC3525 the ss pin Capacitor is charged with a current source, but at what time will soft start be finished? When the voltage of Css reach the internal reference Voltage or when the voltage of Css rises above the REF/EA+ level? How about UCC28250?

over 7 years ago

0 Brian Johnson96 over 7 years ago

TI__Expert 3200 points

Hi Gu, AN AE will be responding to your question soon.

0 Oliver Pan91 over 7 years ago

TI__Intellectual 2230 points

Hi Chenjie,

When UCC28250 is enabled, the 27-µA internal charging current at the SS pin is turned on and begins to charge the soft-start capacitor until its voltage reach 3.6V (typical), voltage in SS pin will be clamp at 3.6V generally. For UC3525, it will be charged and clamped to VREF voltage level.

Regards, Oliver

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0 gu chenjie over 7 years ago in reply to Oliver Pan91

Prodigy 110 points

but the UCC28250 datasheet says on Page20 that soft-start time is considered finished once the ss pin voltage is above REF/EA+. so my question is, when output voltage is reach the normal voltage level before ss Pin rise to 3.6V, is there any conflict between softstart and normal voltage regulation?

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UC3525A: Questions about the soft start with UC3525A and UCC28250