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Original question:

UCC256402: Soft start issue

UCC256402: UCC256402: Soft start issue

A M
Prodigy 115 points
Part Number: UCC256402

Hello,

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1244602/ucc256402-soft-start-issue?tisearch=e2e-sitesearch&keymatch=soft%20start%20UCC256402#

Further to our discussion  soft start issue as link above,

We changed the vcr capacitors but it did not improve, we increased the soft start capacitor it is taking longer time to reach final value but initial it is going to 18-20V and dropping 5 to 6 volts and increasing also the output waveform shape is not consistent sometimes it is reaching 28V in 5ms and sometimes it is going to 20V and dropping to 15V and again reaching 28V.
Initial start up frequency is 500kHz and quickly reducing to resonant frequency within very short time. we disabled LL/SS pin initial voltage during start up by choosing option 5 but improvement is only minor.

Regards

AM