UCC28950: Noise on Out C and D

Nate Enos

Part Number: UCC28950

Hi Team,

Posting for a colleague.

Overview of Problem:

Our Out A and Out B are always at a 50% duty cycle at approximately 100KHz. However, lines C and D are not always at a 50% duty cycle. In one pulse C and/or D may but much smaller or larger than the next pulse. In general E and F look good as well. I have attached a photo comparing each waveform.

Out A B

Out C D

Out E F

Any ideas what could be causing this?

Thank you for the help,

Nate

over 8 years ago

0 Brian Johnson96 over 8 years ago

TI__Expert 3200 points

Nate,

I will have an AE look into this E2E question.

0 Takey Asaad over 8 years ago

Prodigy 50 points

This problem happen when the sync start to work, i mean once i have E and F this problem appears.

0 Nate Enos over 8 years ago in reply to Takey Asaad

TI__Genius 9430 points

Hi Takey,

A few quick follow up questions from the team:

How does the output voltage look? Is there excess ripple or droop?

Are you close to max load when this happens?

or are you close to the current limit?

Thanks,
Nate

0 Takey Asaad over 8 years ago in reply to Nate Enos

Prodigy 50 points

Hi, we do not have problem with the ripple, and this problem happen at light load once the sync start.

0 Colin Gillmor over 8 years ago in reply to Takey Asaad

TI__Mastermind 25570 points

Hello Takey

Is it the case that if you do not use the SYNC function and let the UCC28950 run on its own internal oscillator that there are no problems with the signals ?

I think the first thing to eliminate is the possibility that the device is not properly synchronising to the external SYNC signal.

what is the free running frequency ?
What is the sync frequency that you are putting on the SYNC pin and what is its duty cycle
What is its amplitude and what are the rise and fall times (approx)
Have you configured the device as a 'Slave' ? (timing resistor between RT and GND)

Regards
Colin

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UCC28950: Noise on Out C and D