UCC28950: when clamped V_COMP to 2.7V

ACGUY

Part Number: UCC28950
Other Parts Discussed in Thread: UCC28951

Hello E2E,

I know that the UCC28950 has issue when overcurrent protection behavior with maximum duty operation from following thread information.
I also learned that clamping the COMP pin to 2.7V is an appropriate countermeasure.

e2e.ti.com/.../ucc28950-at-current-limit-and-maximum-duty-cycle

Please let me know the side effects of this measure.

COMP terminal voltage for hiccup operation and transition to latch stop mode
Are you using it?
Is the COMP terminal voltage used for functions other than the above?
What does the UCC28950 do when overcurrent occurs at maximum Duty when the COMP terminal voltage is clamped to 2.7V?

Best regards,
ACGUY

over 3 years ago

0 Yunsheng Qu over 3 years ago

TI__Genius 9790 points

Hi, ACGUY

based on the issue when UCC28950 trigger overcurrent protection behavior with maximum duty, TI has upgraded UCC28950 to UCC28951. Then there is no such issue with UCC28951.

Here is app note to explain it. I suggest you to use UCC28951 then the VCOMP is not need to be clamped.

https://www.ti.com.cn/cn/lit/an/slua853/slua853.pdf?ts=1650937759827&ref_url=https%253A%252F%252Fwww.ti.com.cn%252Fproduct%252Fcn%252FUCC28951

Yunsheng

0 ACGUY over 3 years ago in reply to Yunsheng Qu

Guru 11170 points

Hello,

UCC28951 is not available due to recent semiconductor market conditions. Will TI sell the device? TI won't sell the device, right?
We must continue to use UCC28950.
Please answer the question.

Regards,
ACGUY

0 Yunsheng Qu over 3 years ago in reply to ACGUY

TI__Genius 9790 points

Hi, ACGUY

UCC28951 is normal to sell in TI. It is confirmed.

Yunsheng

0 ACGUY over 3 years ago in reply to Yunsheng Qu

Guru 11170 points

Hello,

I got a reply about lead time is more than 70 weeks for UCC28951 from local disty.
Therefore, we can't to change the device from 950 to 951 soon.

Please answer the question.

Regards,
ACGUY

0 Yunsheng Qu over 3 years ago in reply to ACGUY

TI__Genius 9790 points

Hi, ACGUY

Clamping VCOMP=2.7V can prevent UCC28950 operating in Max duty mode, because the highest value of RAMP internal is 2.8V. Then the abnormal behavior of OUTE/F is gone.

The side affect of clamping VCOMP is UCC28950 cannot enter hiccup mode, which is not used by many customers since cycle by cycle current limit function can protect power stage.

Yunsheng

0 ACGUY over 3 years ago in reply to Yunsheng Qu

Guru 11170 points

Hello,

What does the UCC28950 do if the current reaches the trip point with the COMP clamped to 2.7V? Does the device narrow Duty if the UCC28950 does not enter hiccup mode under overcurrent conditions?

Regards,
ACGUY

0 Yunsheng Qu over 3 years ago in reply to ACGUY

TI__Genius 9790 points

Yes, it still have cycle by cycle current limit.

Yunsheng

Power management

Power management forum

UCC28950: when clamped V_COMP to 2.7V