UCC28631: pin 5 output

Aaron Spaete

Expert 4275 points

Part Number: UCC28631

Team,

My customer has the following question:

I am having some trouble with device.

I have the VDD up, but no transformer connected at the moment.

My schematic is pretty much the same as in the datasheet, as a Quasi Resonant Flyback with input voltage of 270VDC.

With no transformer I should see some Gate Drive on pin 5?

Regards,

Aaron

over 5 years ago

0 Kuan Wei Chen (Kevin Chen) over 5 years ago

TI__Genius 9710 points

Dear Spaete,

I am not sure why your customer will test the circuit with no transformer here.

If there is no transformer, no signal for Vsense pin.

This pin will collect the output information, also have protection when pin is open.

Do you test the circuit with 270VDC input?

Because IC also have UVLO function.

Best Regards

Kevin

0 Jerry Isahaq over 5 years ago in reply to Kuan Wei Chen (Kevin Chen)

Prodigy 30 points

Hi Kevin,
I did put the transformer in and got it running. My input voltage is 270VDC nominal. I got it to start up at 170VDC and I can increase the input to 270V and still runs. However, once I turn the input off at 270V and turn it back on, the PSU would not startup. My current sense is through a 50:1 CT with a burden resistor on 10 OHM and my output power is around 80W.

0 Kuan Wei Chen (Kevin Chen) over 5 years ago in reply to Jerry Isahaq

TI__Genius 9710 points

Dear Jerry,

Can you kindly provide the schematic?
I think you might trigger the OVP function.

Best Regards
Kevin

0 Jerry Isahaq over 5 years ago in reply to Kuan Wei Chen (Kevin Chen)

Prodigy 30 points

Kevin,
I cannot provide the schematic since this is for a defense contract. However, the schematic is pretty much the same as the one in the datasheet. I have 4 outputs and the feedback winding is fed into V_SENSE.
I will check the OVP and see if that is causing problem at startup.

Thanks.

Jerry.

0 Jerry Isahaq over 5 years ago in reply to Jerry Isahaq

Prodigy 30 points

Kevin,
Just another piece of info. when the PSU wouldn't start up, I get a series of pulse (18) on the SD pin. I do not know how to decode that, maybe you can tell me what that mean.
Thank you.

0 Kuan Wei Chen (Kevin Chen) over 5 years ago in reply to Jerry Isahaq

TI__Genius 9710 points

Dear Jerry,

Thanks for the information.

Base on TI's primary side regulated troubleshooting.

The reason might be "2.5: on time detection", which cause by CS pin doesn't reach Ipp(min) after VDD UVLO.

After you turn off the input voltage and restart it, the IC might in the UVLO status.

I hope this information will help you find out the bug.

Or you can go through the document for more information.

Best Regards

Kevin

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UCC28631: pin 5 output