UCC28730-Q1: non-Isolated Flyback

Dear Tateo-san,

Thanks for promoting TI's solution to your customer.
I tried to find our inner database, but can't find UCC28730 with non-isolated design. So I am sorry can't help on this.
The TIDA-00628 should work well with UCC28730.
If there is anything I can help, please feel free to let me know.

Best Regards
Kevin

Hello Tateo-san,

Thank you for your interest in the UCC28730-Q1 controller. I didn't know that Kevin answered you while I was composing this reply, but I decided to post my reply as well.

Can you please clarify if the design is to be a non-isolated “Flybuck” or a “Flyback”? The title of your post says Flyback, but your question says Flybuck. The UCC28730 cannot be configured to operate in a Flybuck topology.

Assuming that you want a 2-output non-isolated flyback circuit, I believe that the TIDA-00628 can be modified to conform to the input and output parameters that you listed. Here are my observations and concerns about it:

1. Your maximum input voltage is lower than the TIDA spec, so you do not need the Q1 and V2 regulator components at the input.
2. Your minimum input voltage is higher than the TIDA spec, so you can optimize the transformer turns ratios to minimize primary currents and losses.
3. You have two outputs being controlled by primary-side regulation (PSR) so cross-regulation might be a problem if the output currents can vary independently and widely.
4. You can use the 15V output to provide the controller bias current and VS signal source, as shown in the TIDA design.
5. Regulation of 7-V winding may be loose, depending on how much load current varies.
6. UCC28730 is intended to drive a MOSFET. To use the “snubber-less” design like in TIDA-00628, you may need a MOSFET with 650V, 700V or 800V rating, depending on the leakage inductance energy of the transformer. Or you can use a 600-V MOSFET with a voltage clamp circuit across the primary winding as in typical flyback designs.
7. The switching frequency of the UCC28730-Q1 can go extremely low (down to ~32Hz) in order to meet stringent stand-by power requirements. A PSR controller operating near such low frequencies will be very slow to respond to load steps unless it has a wake-up function. The UCC28730 uses the UCC24650 to provide this output monitoring and wake-up. However the UCC24650 is NOT qualified to automotive Q100, so if you need to use the UCC28730-Q1 for an automotive application, the wake-up function will need to be provided by a circuit (made from –Q1 parts) that emulates the function of the UCC24650. But if there are no load steps, or can be controlled to increase at a slow rate, then the wake-up is not needed and a large output capacitance should be sufficient. Or a minimum load can be added to keep the switching frequency higher.
8. If extremely low stand-by power is not required, an alternative controller that would work the same way is UCC28700-Q1. This has a minimum frequency of ~1kHz, so response to a sudden load step is much faster.
9. Here is a link ( www.ti.com/.../PMP10866 ) to a similar 7-W design for a multi-output flyback using the UCC28910 device. This part is not Q100 qualified. I suggest to review it simply as an indicator of how more than one winding may be applied with a PSR controller.

I hope this addresses your concerns.

Regards,
Ulrich