UC3854: Open-loop testing

Mason Noh

Expert 2490 points

Part Number: UC3854

Hi TI team.

Could you provide open loop circuit diagam of UC3854?

Like a bellow circuit.

Acutually, our customer wants to test IC before SMT.

When UC3854 working open-loop, PWM duty is not oscillate?

If they measure GTDRV(PWMOUT), They can sort out abnormal products?

over 5 years ago

0 John Griffin1 over 5 years ago

TI__Mastermind 34465 points

Hello Mason,
I have requested a copy of this from the product test group.
I will post this as soon as I hear back.
Regards
John

0 John Griffin1 over 5 years ago in reply to John Griffin1

TI__Mastermind 34465 points

Hello Mason,

I was unable to get a schematic drawing for the open loop test.

What I was able to find was a written list of the signals applied to the pins on the UC3854:

This will help you view the GTDRV and reject abnormal parts.

Hope this helps

Regards

John

0 Mason Noh over 5 years ago in reply to John Griffin1

Expert 2490 points

Thank you for your support.

Please let me know GTDRV oscillation when open loop test. Is it abnormal?

Because some devices is not oscillate but another devices is oscillating like a below waveform.

0 John Griffin1 over 5 years ago in reply to Mason Noh

TI__Mastermind 34465 points

This oscillation is not normal and there also seems to be large switching spikes even on the good ic
I would look at the layout of the test fixture.
Is GTDRV going below ground and above VCC ?
It may be noise pickup or not enough decoupling on VCC or VREF
What does the oscillator (CT) waveform look like ?

0 Mason Noh over 5 years ago in reply to John Griffin1

Expert 2490 points

Thank you John~

I will check layout and noise.

And I measured CT waveform, it's normal.

Power management

Power management forum

UC3854: Open-loop testing