UCC28950: UCC28950 Urgent question about in the waveform between OUTC and OUTD?

Bob Lee62837

Part Number: UCC28950
Other Parts Discussed in Thread: UCC28951

Dear support member.

The customer is mass producing UCC28950.
This project is Urgent.

IC is broken and I have a question.

（Situation)
There is no disturbance in the waveform between OUTA and OUTB.
However, in the waveform between OUTC and OUTD, there is a part where Duty 50% is not continuous and is flying.

（Question)
Q1.
Is the IC abnormal when the waveform is not continuous?

Q2.
If the IC is abnormal, what can be the cause?

I attached waveform.
Could you check it?

UCC28950_Question_191115.pdf

Best regard.
Bob Lee.

over 5 years ago

0 Peter Meaney over 5 years ago

TI__Mastermind 31580 points

Hi Bob,

One thing the customer can do is swap in the UCC28951 which is the latest version of the IC which is more robust at high duty cycles. The part is pin 2 pin compatible with the UCC28950 and there are no other changes required on the PCB.

Can you tell me what operating condition the customer is seeing this issue ? Is it at a steady state condition ? It looks like the controller is close to max duty cycle, so maybe minimum input voltage at high load?

Regards

Peter

0 Bob Lee62837 over 5 years ago in reply to Peter Meaney

Mastermind 7230 points

Dear Peter Meaney,

Thank you very much for reply.

As I are checking the customer the operating condition, I will feedback it.

Because you encourage device changes, let me ask question.

（Question1）
From this waveform,
Is there IC a problem?
Or
No problem?

（Question2）
Why do you recommend UCC28951?

Best regard.
Bob Lee.

0 Peter Meaney over 5 years ago in reply to Bob Lee62837

TI__Mastermind 31580 points

Hi Bob,

With the UCC28950 at maximum duty cycle and under current limit condition there can be a missing pulse condition.

The fastest way to determine if this is the root cause of the problem that the customer is seeing is to replace the UCC28950 with the UCC28951.

TI has an application note on this,

Regards

Peter

0 Bob Lee62837 over 5 years ago in reply to Peter Meaney

Mastermind 7230 points

Dear Peter Meaney,

Thank you very much for reply and application note.

As I are checking the customer the operating condition, I will feedback it.

Best regard.
Bob Lee.

0 Colin Gillmor over 5 years ago

TI__Mastermind 25570 points

Hello Bob

This looks very much like the controller is operating in Current Limit and at Dmax. I suggest that the customer try the UCC28951 which is a pin for pin, 100 % compatible device which is intended for use where Current Limit at Dmax conditions can happen.

The customer has only to change the IC, no other component changes are needed.

Regards

Colin

0 Bob Lee62837 over 5 years ago in reply to Colin Gillmor

Mastermind 7230 points

Dear Peter Meaney,
Dear Colin Gillmor,

Thank you very much for your answer.

Best regard.
Bob Lee.

0 Bob Lee62837 over 5 years ago in reply to Bob Lee62837

Mastermind 7230 points

Dear Peter Meaney,
Dear Colin Gillmor,

This problem is solved.
Thank you very much for your support.

Best regard.
Bob Lee.

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UCC28950: UCC28950 Urgent question about in the waveform between OUTC and OUTD?