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Author Topic: PIC-P26J50 Separating USB bus power from the board  (Read 1665 times)

dag

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PIC-P26J50 Separating USB bus power from the board
« on: December 21, 2014, 06:25:20 PM »
Hi
I am prototyping an application of a USB based product controller. My MCU is required to setup the peripherals on self powered device on power-up and then go to sleep. It is an issue of digital noise, however when a host is physically connected to the USB bus - then the MCU must wake up from sleep and service the USB communication.
To mock up this on the PIC-P26J50 board I need to separate the board power from the USB power but keep the voltage divider R2, R3 connected to the USB power so that bus connection can be detected by the MCU.
Could you post the relevant PCB layers of that board area so I can figure out what traces to cut /bridge to achieve this configuration or can you suggest how to do that?

dag

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Re: PIC-P26J50 Separating USB bus power from the board
« Reply #1 on: December 23, 2014, 05:05:28 AM »
I ended up cutting the USB +Vdd trace and the C8 trace that continues under the Button to R3. Jumper wire the USB +Vdd pin to R3 and inject independent circuit +5V power across C8. Furthermore the USB_DETECT which goes to RA7 from R2,R3 needs to be rerouted to the INT0 pin or any other pin that can be used as interrupt to wake the MCU from sleep.