The heart of this module is a FP5139 Asynchronous Boost Controller.

It's packaged in TSSOP8 and has different features we have to deal with:

• Soft-Start function
• Short Circuit protection

Basically, this booster module is designed like the Application Information in Figure 14 of the FP5139 datasheet.

Some minor modifications compared to this app note:

• Different Feedback resistors
• Voltage limiter (FP5139: Vin 1.8-15V)

If you look at the picture, following colors correspond to these parts of the app note:

orange: FP5139 chip

yellow: Q1/Q5 totem-pole / push-pull gate driver

pink: MOSFET & Diode (Q2/D2)

blue: voltage limiter (some kind of transistor circuit)

green: feedback circuit filter capacitor and R6 in the app note (lower side of a voltage divider)

turquoise: oscillator settings & soft-start capacitor

red: feedback pin, that's what we need

BTW: The MOSFET was destroyed by me (while removing the heatsink), so your boost module might look different :-)