One Phase of buck converter won't start (UCC27201D application)

Hassan Kelley

The two phases (lets call them A and B) of a buck converter will not work together. Each phase will work fine when the other is disabled. When both phases are enabled only phase A works--Phase B will not start switching. If I turn disable Phase A by remvoing the MOSFET, Phase B will work with no problems.

The design uses two UCC27201D MOSFET drivers in the conventional buck topology (i.e 1 MOSFET, 1 diode). Both UCC27201D are power by 12V and both use a 0.1uF boost capacitor. The input voltage is 56V and the output voltage is about 24V. The design switches at 250kHz.

Any Ideas?

over 9 years ago

0 Kening Gao over 9 years ago

TI__Expert 5900 points

Hi Hassan,

Can you attach your schematic?

Regards

0 Hassan Kelley over 9 years ago in reply to Kening Gao

Prodigy 210 points

I hope that worked. If it doesn't I can email it directly to you.

3034.PCUTGA-P1.pdf

0 Kening Gao over 9 years ago in reply to Hassan Kelley

TI__Expert 5900 points

Hi Hassan,

From the schematic I cannot find the reason.

Have you checked the HO-HS, HS-GND,HI-GND of PhaseB when the issue occured?

I am doubt for the misconnection.

Regards

0 Hassan Kelley over 9 years ago in reply to Kening Gao

Prodigy 210 points

I resolved the problem. A race condition existed between the two UCC27201D VDD's. VDD (12V) is generated from the input power (see section 3D on the schematic). Whichever UCC27201D powered up first started switching while the loser was locked out. I fixed the problem by temporarily borrowing +V1 (12V and always on) for the for VDD. Now both UCC27201D's are powered up and ready long before the input voltage (+VDC) is applied.

Thank you very much for your help.

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One Phase of buck converter won't start (UCC27201D application)