STM32 auto programmer, ultra-miniature with no external circuitry, powered by DC-DC converter.

1. Project Images:

Main image (
front and
back)

2. Main Parameters:

This project has been verified and can achieve automatic downloading to STM32.
Small size (2.63cm long x 1.7cm wide), aesthetically pleasing, with side-soldered pin headers and no protrusions on the back.
Uses a DC-DC driver, supports 5V/3V3 output switching, and can directly power high-load microcontrollers, such as a 99-pin WS2812B keyboard, with extremely low heat generation.
SY8089A1ACC supports input voltage range from 2.5V to 5.5V, with a maximum output current of 2A.
Uses CH340X to achieve automatic downloading without external circuitry, such as STM32, ESP32, and 8266. 3. Instructions for Use:

Select the VCC voltage using the switch for adaptation, and connect VCC and GND to your microcontroller.
Connect RXD to the MCU's TX, and TXD to the MCU's RX.
Connect NRST to the MCU's RST. If you need an additional reset button, connect a 2K resistor in series between NRST and RST.
Boot0 needs to be directly connected to your microcontroller because the STM32 requires a low pull-down resistor to run the program. It's recommended to move the 4.7K pull-down resistor from the downloader to the microcontroller, as shown in
the diagram. The settings should be as follows: RTS high level to off, DTR low level to bootloader.

When purchasing components, note that the inductor package used in this project is 252012 (1008). 1.5Uh inductors may be difficult to find; 2.2Uh inductors can be used, but it's recommended to replace them with two 10Uh 0805 inductors.
The switch model is MINI MSK12CO2, which is also not easy to find. You can buy it from LCSC online store. Make sure the pins are symmetrical; you can also directly short-circuit them.
Your STM32 microcontroller should always have BOOT1 pulled down, and BOOT0 should use a 4.7K pull-down resistor. Do not solder the 4.7K pull-down resistor from the downloader, as they are shared.
The selection of the Schottky diode also affects download speed. You can directly short-circuit it or replace it with a smaller package. Testing showed that the 1N5819WS and SD103AW diodes failed to download. Using a diode can resolve conflicts when connecting a microcontroller to an external serial port device.
The ESP32/8266 requires circuit modification; the 4.7K resistor needs to be moved to series between the CTS and DTR.

Version V2.1 (July 18, 2024): Changed the inductor model and package, and changed the Schottky diode model.
Version v2.0 (July 18, 2024): Officially released this project; images are from version v2.0. 6. Related Links:

One-click microcontroller serial port download without external circuitry;
USB to serial port chip CH340
(to be added)... 7. Demo