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STM32F407G-Discovery-STlinkV2(V2.J25.M13) - Boot fail using external power supply

Question asked by Pankaj on Apr 6, 2016
Latest reply on Apr 7, 2016 by Pankaj
Hello all,

I have bought STM32F407G-Discovery evaluation kit its "STM32F407G-Disc1- MB997D". Apparently I was unable to boot kit after programing  using external power supply e.g mobile phone usb charger or +5V to applied to 5V pin. It boots up fine with PC usb port as well USB port of oscilloscope but not with external +5V supply.

After scratching head for while I found on powering kit using PC there is some communication going on between debugger (stm32f103) and USB host(PC). After this communication on board debugger (stm32f103) pulls NRST going to STM32F407 and also puts MCO out pin in high Z(guessed). This MCO from stm32f103 supposed to output 8Mhz to MCU xxF407 on PH0 pin.

Without initial communication between debugger and host PC above two things don’t happen so booting never happens. My debugger has version of "V2.J25.M13 STM32 Debug+Mass storage".

So way around is disconnect NRST pin by removing SB11 solder bridge and disconnect MCO pin by removing R68. Schematics on page no 32 of user manual (UM1472).

After above trick my board boots up fine using external power supply. I am not sure this initialisation functionality is intended on V2.J25.M13 firmware or its bug? can some buddy try to replicate this issue?