UCC256404: How to extend the soft start time

Hi Ryu,

You need to increase the CLL/SS capacitor value to increase the soft start time. Also, soft start time is effected by the initial LL/SS pin. You can find the soft start calculations in page number 63 of the data sheet 

UCC25640x LLC Resonant Controller with Ultra-Low Audible Noise and Standby Power datasheet (Rev. E) (ti.com)

You can also use the design calculator for finding these passive component values to change the soft start.

https://www.ti.com/lit/zip/sluc675

Regards

Manikanta P

Hi Ryu,

As mentioned in my previous post, You can use Design calculator to find the capacitance value at soft start pin based on the soft start requirements. You can further increase the LLC start time by increasing the BLK start threshold voltage. 

Regards

Manikanta P

Hi Ryu,

You are correct. You can not connect more than the 470nF. 

Setting BLK start value:

Here you can observe that, when PFC output voltage reaches Vbulk start threshold voltage, LLC starts switching. So, By changing this Value, you can further delay the start time of the LLC. You can refer page number 57 of the data sheet to set the BLK start and stop values.

Regards

Manikanta P