UCC28720: Can we design?

Hello Sanyogita,

Yes, the UCC28720 can be used for a 2.5-W isolated power supply module (5V, 0.5A).
I will refer the junction temperature issue to the Webench modeling group to find and fix that calculation problem.

It does raise a question as to whether any of the other component-value calculations are affected by the Tj issue.
I'll have to run a trial design win Webench to see if I recreate this, then check the components against the datasheet design procedure. In any case, it is prudent to verify all component values against the design procedure in the datasheet.

Regards,
Ulrich

Hello Sanyogita,

The Webench team found the problem in junction temperature calculation and fixed it. But revisions are loaded up on Mondays, so unfortunately you won't be able to use Webench for the UCC28720 in your application until then.
But you are still able to use the datasheet procedure or use the Mathcad or Excel calculation tools available for the UCC28722, found under Software tools in the UCC28720 product folder on the TI website. The UCC28722 does not have the integrated HV start-up feature, but the rest of the design calculations for UCC28722 and UCC28720 are the same.

Regards,
Ulrich

PMP11787 Rev_A Schematic.PDF

Sanyogita,

Thanks for your interest in TI here. Ulrich is off now on holiday so I will offer some additional assistance here.

To your question, you are correct -Isolated power designs do not include the "simulation" tab like you might see with our DC/DC converters. The transformer makes it quite complicated to simulate in an online environment. For simulation capability we do include Spice models in the "Tools and Software" tab of the product folder for each of the products like here for the UCC28722:

In general, webench for AC/DC and isolated power designs is used more to assist with product selection, component selection, estimates on efficiency, and providing calculated operating points of stresses like component voltage and current as well as component power losses.

Just in case you had not noticed other solutions, I see these as your main options here:

UCC28880: Integrated High Voltage Startup and High Voltage MOSFET-can use as isolated Flyback with opto coupler if you like.

UCC28910: Integrated High voltage Startup and HIgh voltage MOSFET-can use as isolated flyback with NO opto coupler for less components

UCC28720: what you were looking at here. No-opto PSR flyback with integrated HV startup FET for lower standby power/faster startup time than resistive startup.

UCC28722: same as UCC28720 but no integrated HV startup FET(uses resistive startup) but offered in a smaller, lower cost SOT-23 package(compared to SO-7 like UCC28720).

I'm not sure what voltage regulation you need. In general, the PSR type designs can achieve +/-5 Vout regulation while an opto-based controller can achieve +/-1%. The PSR has the advantage of fewer components though and longer lifetimes by removing the optocoupler.

I personally like the UCC28910 for your requirements because it's the most integrated solution. I found a UCC28910 design and attached the schematic here as a point of reference. This design was not built but you should be able to use it as a reference point for yourself during your design if you would like.

Regards,

John