Hello,
We are currently implementing a split cap half bridge LLC, 480W, 48Vout, 390Vin (20 to 25 Vpk-pk ripple). Output will have SR's. Natural convection (no fan).
The output can go from 42V to 60V, which presents a challenge as we will be in burst mode full power for some of the Vout range. We have been testing with ONSEMI's NCP13994 eval board, and when in burst mode there is no way to control the upper switching frequency limit. The upper limit is based on the tank operating point and tank values, so I am seeing based on there design the frequency max limit can get 500kHz or higher. At 100W, 25C ambient, weak fan blowing, the SR's are approaching 75 or 80 degrees. For us, at 480W there is no way the SR's will survive given the Fsw_max we would actually hit, which would be the IC's limit of 750kHz.
We need a solution where we can accurately control the switching frequency limit, especially the max frequency, like you could in a digital design when in burst mode operating at full power. Can the UCC25660 accurately control the max switching frequency (mosfet Fsw - not burst mode frequency) when in burst mode?
I see there is the TSET pin limits the Minimum operating frequency limit for the LLC, as well as the maximum dead-time (so a theoretical max frequency).
Can you please explain if or how this IC sets a minimum frequency limit and maximum frequency limit?
Thanks