Hello,
I tried to develop my first µC board inspired by the " adafruit feather STM32F405 express". For layout I used KiCad and the board is made by Chinese PCB manufacturer JLCPCB. To activate the DFU bootloader, the BOOT0 pin must be connected to 3.3V pin and then the reset button must be pressed. Everything worked like the Adafruit Feather, but I have to wait more than a minute ( exactly 01:32.38 ) after pressing the reset button until the bootloader is activated.
The HSE crystal oscillator (12MHz, LCSC part number is C165948) works . I tested it with oscilloscope.
USB is " TYPE-C-31-M-12 " ( like adafruit feather ). D+ and D- pins of the µC are PA12 and PA11. The trace width is 0,261mm ( differential pair ) and was calculated with " JLCPCB Impedance calculator " for a 90 ohm impedance. The trace length is 66,33 mm.
USB pin is connected to a voltage regulator AP2112-3,3V, P-channel mosfet ( DMG3401LSN-7 ), a battery management (MCP73832) and two other pin header.
I didn't found an explanation why it takes exactly 01:32.38 ( 8 attempts ) each time after pressing the reset button for the bootloader to activate.
I hope for a feedback and thanks in advance
With kind regards
Bough
