We are using UCC28720 as per attached image below.
In few of the power supplies, we found Parts R91, R92 ( Current Sense resistors), U1 ( Switcher) , T1 ( Transistor connected to the switcher drive) and R2 ( Transistor Base drive ) are damaged.
The damage is happening in few power supplies(<2%).
The Powers supply is subjected to first power on at 230V, does not turn on and subsequently found that the parts are damaged.
Our specifications are as below.
Lp:330uH, Vinmin=44V, Vinmax=277V, Vout1=6.5V, Iout=0.1A, Vout2=5V, Iout2=0.35A.
What can be the possible causes of this damage? Please suggest.