Sorry for very late reply on your help. Im still get stuck on this and near crazy level about fet driving.
For schematic, i doing prototype on 2 separate.
One is test Poorman’s Buck from Ledartist (instructable, link: https://www.instructables.com/id/Poormans-Buck/).
And one is based on HV9910B led driver.
I need mosfet driver because in my country, to find out exactly needed mosfet is very challenging especially logic level fet. So its better do somthing with fet driver and normal fet like IRF5xx series.
On Poormans Buck, i had change a little on original circuit to handle over 3A. And i found that with push pull gate driver (i use B772 and D882 transistor pair), i recieve ahalf voltage from power rail on mosfet gate. I dont know how or why but i know my mosfet reach 130*C. Bad situation.
On HV9910, the datasheet said i can directly drive a normal fet and just take care on Qgate (25nC for <100kHz, 15nC for over 100kHz). But gate voltage of HV9910 just have 7.5v (equal VDD pin, internal voltage regulator). What happen if a IRF 530 or 540 or everything like them will be drived at that voltage? I think they not fully turn on to out of ohmic region.
Thank all very much. Im keep coninue find my way to use mosfet, thank thank thank… T_T