Hi,
I am working on the usb bootloader with the DRV8312EVM board and the 28069 control card. Yesterday I found the external 12V power for the evaluation board will make the bootloder not work normally.
We use the usb cable(inserted into the J200 slot in the 28069 control card) to downlaod the hex code when the bootloader works.
At this time, if we enable the external 12V power for the evaluation board, the bootloader will not work normally(dfuprog.exe can not find the usb device or it can not download the hex file normally). If disconnecting this 12V power, the usb cable will get power and make the MCU to run, the bootloader will work normally.
After the bootloader downlaod the application hex file, to enable the external 12V power and/or insert the usb cable, the MCU can boot to the Flash application.
In the evaluation board schematic, A 5V power converted from the external 12V power is connected with another 5V power(from the usb cable) by JP2. But if I remove the JP2, the external 12V power will make the bootloader abnormal again(dfuprog.exe can not find the usb device or it can not download the hex file normally). To remove the JP2 can not solve the above problem. If I do now remove the JP2, the VR2(convert from external power into 5V) chip become very hot.
How does the external affect the usb interface?
Thank you
Fei
