UCC256404: Power management forum

Rahamadullah A

Part Number: UCC256404

Hi TI team

I have query on UCC256404 LLC controller

1. If i use capacitor split method for Half bridge LLC and the split capacitors due to its tolerances top and bottom half voltage will have different values(lets say 210V on top cap and 190V on bottom cap) will the transformer flux walk and saturates? will the LLC operate properly?

2. To avoid the variations in the split capacitor if i connect in configuration as in pg no 46 of UCC256404 IC will there be any problem other than transformer saturation during startup?

Thanks

Regards

Rahamadullah

1 month ago

0 Mike O' 1 month ago

TI__Guru 69675 points

Hello,

Your inquiry is under review and I will get back to you shortly.

Regards,

0 Mike O' 1 month ago in reply to Mike O'

TI__Guru 69675 points

Hello,

1. I believe even if the capacitors are mismatched slight due to tolerances that the DC voltage at that node will be roughly half the input voltage.

>If you had a single SR capacitor the DC voltage across the resonant capacitor would be half the input. The reason for this is that node is actually the output of LC filter when compared to the switch node.

>The benifits of these two capacitors are

a. Lower RMS current in each capacitor.

b. Pre charging the voltage at that connection between the magnetizing inductance and the resonant capacitor before switching begins. This speeds up

startup.

2. You should not run into transformer saturation if you configure based on the recommendations of the data sheet and what is described above.

Regards,