UCC28710: UCC28710 Startup Issue

Kalyani Raut

Part Number: UCC28710

Hello Team,
I have designed an AC/DC charger with specifications of 58V / 200W.

During light-load test, output reaches 58V (design target). But when load current is gradually increased, converter shuts down automatically. After shutdown, converter does not restart.

Checked primary side:

Proper voltage present at HV pin
VDD capacitor charges up to 21V and then discharges repeatedly
No DRV pulse observed
No VS/CS pin activity

Please suggest the possible reason and solution for this issue.

Regards,

Kalyani

5 months ago

0 Anita Yadav 5 months ago

TI__Expert 7395 points

Hi Kalyani,

Please take a look at Vaux waveform, once the soft-start is completed, what is voltage across Vaux is at knee point? Can you provide proper vertically zoomed waveform of Vaux, Vdd, Vcs & Vout of the last switching cycle. Vs pin is sensitive pin and probing directly Vs pin, might affect controller working, kindly avoid it instead probe across aux winding for any info needed for Vs pin.

Also, you can refer below app note which provide insights on debugging steps for TI PSR controller including UCC2871x.

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/508706/trouble-shooting-startup-issues-with-ti-psr-flybacks-ucc28700-ucc28701-ucc28702-ucc28703-ucc28704-ucc28710-ucc28711-ucc28712-ucc28910-ucc28911-ucc28720-ucc28722-etc

slua783.pdf

Further, if you want me to look at design, can you provide complete design specs and design schematic file along with transformer datasheet?

Thanks

Regards

Anita

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UCC28710: UCC28710 Startup Issue