can I use UCC28710 or ucc28910 for below Isolated DCDC ?

Hi Jiaying,

The UCC28710 and UCC28910 are designed to work from univerals mains input voltage range , the 25V is probably not high enough to allow the internal HV regulator to charge the C1 cap on Vdd, check the voltage waveform on the Vdd pin.

If the appilcation has an input voltage range of 24 to 26V you will need to use an LM5021 controller.

Regards

Peter

Hi Peter
Thanks for your advise.
What about HV pin open and VDD pin directly connected to the 24V？
24V for UCC28910 maybe is high enough?
VDDON VDD turn-on threshold VDD low to high 9.0 9.5 10.0 V
VDDOFF VDD turn-off threshold VDD high to low 6.0 6.5 7.0 V
VDDHV(on) HV current source start VDD high to low 4.8 5.2 5.6 V
ΔVUVLO UVLO hysteresis VDDON – VDDOFF 2.8 3.0 3.2 V

Regards,

Jiaying

Hi Jiaying,
I believe you should be able to use the 24V input to connect to VDD and start up but you will not have the hiccup fault protection; the device may latch off at a fault because VDD won't be able to fall below UVLO for reset. But if that's not an issue then it should be ok.
Also, the UCC28910 HV is actually the DRAIN pin and it will start charging the VDD cap when it rises to 20V, but limiting the DRAIN to 24V will limit the current that the internal HV circuit can source to continue charging VDD so it may take a while for full turn on.