Startup current for buck converter controller

Thread Starter


Joined Jun 10, 2019
In this Reference Design, a buck converter was designed using the UCC28881 controller.

According to the datasheet, the HVIN pin is a current source, with an internal supply current of 58 uA typically. Also, the minimum voltage at this pin is 30V.

In the design above, the HVIN pin is connected to the VIN net, which is the cathode of diode D6+D7, after the string of resistors R6-R15. The design says the minimum input DC voltage is 235 VDC.

My question is:
If I want the design to operate with lower DC voltage, that is, 100 VDC, what modification would I need to do? Would the string of resistors allow enough current for the HVIN pin? Do I need to lower the value of the string resistors? It seems also this resistors would dissipate much power at the highest voltage level.
I'd appreciate any guidance to further understand the input side of this circuit.