UCC256304: Vout dropping with load step

Alberto Doronzo

Expert 4840 points

Part Number: UCC256304

Hi,

I have a customer that is using the UCC256304 in the EVM (in AC input mode) and he is having issues.

The EVM power up fine and can take loading on the output if it start at no load and increase it gradually.

However, if a load gets applied directly ,the output goes to zero.

He did the mods in the eval board test report and also tied TP5 to TP10 for HV startup.

Vbus is ~360VDC. It starts at about 340VDC.

Is there anything that might be causing this on the board itself (configuration).

Thank you!

Regards,

Alberto

over 6 years ago

0 Benjamin Lough over 6 years ago

TI__Mastermind 27145 points

Hi Alberto,

Does the output voltage drop out every time there is a sudden change in load step or only sometimes? One possibility is that the opto-coupler is saturated and due to the delay for the opto to get out of saturation, there is a delay in the response form the controller and the otuput drops out.If this is the case, you can add a 4.3V zener in the secondary feedback network to prevent the opto-coupler saturation

Best Regards,

Ben Lough

0 Alberto Doronzo over 6 years ago in reply to Benjamin Lough

TI__Expert 4840 points

Hi Ben,

thank you for the information!

Best regards,

Alberto

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UCC256304: Vout dropping with load step