UCC28740: UCC28740 Multiple feedback resistor question.

Dear Bob,

Thanks for promoting TI's solution to your customers.

If you calculate by superposition on 12V-out and 5V-out.

You will find out two output provide different proportion on the LM431's Ref pin.

12V==>0.35V, 5V==>2.09V, total 2.44V.

By the result, we can know that 5V will provide a bigger portion to regulate the circuit, which causes the 5V rail to have a more stable output(as below picture, from TI training PPT).

So I will suggest you build the circuit first and fine tune the resistor value to get the cross-regulation result which you can accept.

E2E question, have good material you might be interested in responses.

TI training material, you can go through the video or download PPT.

Dear Bob,

Normally, this kind of multi-output on one transformer is suitable for low power design. As you can see, the output regulation is not very well in the picture I provide. It will be worse if for higher power design. LLC is suitable for higher power one output design, instead of low power multi-output.

Best Regards
Kevin

Dear Kuan Wei Chen,

Thank you very much for reply.
May I ask a question?

Is it possible to control 12V, 60V multi-output feedback control with the LLC controller?

Best regard.
Bob Lee.

Dear Bob,

Multi-output LLCs have been done before with UCC25630x. It should be fine but depends on how tightly regulated they need each output voltage to be.

Best Regards
Kevin