LM5122: Output Overshooting at restart after quick supply toggle

Hiroaki Kohriyama

Part Number: LM5122

Hi team,

My customer has seen huge overshooting in 2ms after quick supply toggle.

Load is only 140uF cap (other load is open by trace cut). Supply is dropped from 12V to 3V at restart. Output is dropped from 45V to 38V, and raised up to 70V at 2ms after startup. The switching node waveform is not captured yet.

Is there any care-about for such momentary supply toggling ?

Thanks, Hiroaki

over 6 years ago

0 Youhao Xi over 6 years ago

TI__Guru* 78370 points

Hi Hiroaki-san,

Thank you for reaching out. It sounds like the lack of soft-start after the supply voltage recovery. You should program the UVLO such that the circuit can hit UVLO during the supply voltage drop, say 6V. Then, when it recovers, the circuit will go through soft start and the output overshoot can be avoided.

Hope this clarifies.

Best Regards,
Youhao Xi, BCS Applications Engineering

0 Hiroaki Kohriyama over 6 years ago in reply to Youhao Xi

TI__Intellectual 760 points

Youhao-san,
I found the UVLO resistor divider on the customer's schematic, which is 100k/47k. And VIN bottom on their scope shot is about 4V. So it seems just above the UVLO threshold. Thanks so much for your prompt input !!
Hiroaki

0 Youhao Xi over 6 years ago in reply to Hiroaki Kohriyama

TI__Guru* 78370 points

Hiroaki-san,

Thank you for the update. Lets close this thread. You can reopen it by following a new post.

Again, thanks,
Youhao

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LM5122: Output Overshooting at restart after quick supply toggle