UCC256304: UCC256304

Konstantin Nikiforov

Part Number: UCC256304

I've made power supplie using ucc246304 controller. One is functioning properly as expected while second one not. When turned on under load it generates 1/2 to 2/3 output voltage and works at 660 kHz. If turned on unloaded and then put under load then everything looks fine. Please advise what's wrong.

over 5 years ago

0 Benjamin Lough over 5 years ago

TI__Mastermind 27135 points

Hi Konstantin,

Thanks for reaching out. I would suggest probing LL/SS and BLK pins on the not-working supply. If the LL/SS voltage does not match the BLK pin voltage, the device may be going into ZCS protection. If this is the case, I would suggest increasing the bypass capacitance from ISNS to gnd.

Best Regards,

Ben Lough

0 Konstantin Nikiforov over 5 years ago in reply to Benjamin Lough

Prodigy 180 points

Hi Ben,

Thank you for giving me good directions. It turned out that LL/SS pin was shorted to the ground. Now both power supplies work identically. May I also ask if it's normal that RVCC is going up and down within 300mV every 1.1 second and if not what may be the reason for it?

Best Regards,

Konstantin Nikiforov

0 Benjamin Lough over 5 years ago in reply to Konstantin Nikiforov

TI__Mastermind 27135 points

Hi Konstantin,

I am glad you were able to fix this issue. Regarding the RVCC ripple, I have not seen cases where there is 300mV ripple at 1.1s interval. What is your VCC voltage? One possibility is if the VCC voltage is close in value to the RVCC regulation set point. The internal LDO may have very little heardroom and variation in VCC is more likely to show up on RVCC.

Best Regards,

Ben Lough

0 Konstantin Nikiforov over 5 years ago in reply to Benjamin Lough

Prodigy 180 points

Thank you very much!

Power management

Power management forum

UCC256304: UCC256304