UCC28070: UCC28070 PWM signal question

Robin Liu

Intellectual 1930 points

Part Number: UCC28070

Hi team,

My customer debug the UCC28070, they find there is a phenomenon. During power start-up, the UCC28070 would firstly output a small '1' signal. Then wait about 4ms, it could works as normal to output the pwm signal.

So what's the causes? how to deal with this?

if you have any questions, please let me know, thanks.

Regards

Robin Liu

over 6 years ago

0 John Griffin1 over 6 years ago

TI__Mastermind 34465 points

Hello Robin,
Can you please provide a better quality scope plot with a faster time base in order to view the switching waveform.
Please label this waveform which I can only guess is the GDA or GDB waveform.
Also include the AC input voltage and the soft start waveform on the same plot.

Regards
John

0 Robin Liu over 6 years ago in reply to John Griffin1

TI__Intellectual 1930 points

Hi John,

Is the waveform below OK?

Regards

Robin Liu

0 John Griffin1 over 6 years ago in reply to Robin Liu

TI__Mastermind 34465 points

Hi Robin,
Thanks for attaching the waveform.
For the gate drive signals to be present the voltage on VSENSE needs to be >0.75V and VINAC >0.7V
With this condition you should get a clean startup.
It could be that you have a bad solder connection with one of these inputs or your signals from the GDA,GDB outputs are opening and the boost FETs are not switching.
How does the output voltage look during this time ?
It should start at the value of the rectified line voltage (about 300v) then rise smoothly to the value of the set voltage.

Regards
John

0 John Griffin1 over 6 years ago in reply to John Griffin1

TI__Mastermind 34465 points

Hi Robin,
I am closing this post since we are corresponding directly through email
Regards
John

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UCC28070: UCC28070 PWM signal question