I’m gonna high jack this thread for a bit since for now it just adds to what we know about the QX9920. When it comes time to design a board we can start a new thread. For a test rig I’ll need an attiny mcu and an LDO voltage regulator. Fortunately my parts bin had this still in it. 
It dates back to my first year here from This thread it was used to drive 3 xml’s from 3 cells in series. It’s basically a linear driver with the 8 x 7135’s mounted on a separate copper heat sink and a 5V regulator instead of a Zener/resistor. Just to be sure it still works I hooked it up to an XHP 50 and two 14500’s. 
Low, medium, high, no problem, so I desoldered the mcu board from the heat sinked chips since I won’t be using them. 
I’ve removed the 1k resistor and 3 pin chip from the buck driver and my next session will be to connect it to the mcu board(LDO out to QX Vdd and mcu PWM to QX EN. Both boards get B+/B~~, led+/~~ still come from the buck board.