Datasheet

Board Hardware

FIGURE 2-1: PIC18F46J50 FULL-SPEED USB DEMONSTRATION BOARD

Full schematics of the PIC18F46J50 Full-Speed USB Demonstration Board are in

Appendix B. “Board Schematics”.

2.1 POWER MANAGEMENT

The USB interface provides +5V (nominal) power at up to 500 mA for use by USB

peripheral devices. In order to take advantage of this bus provided power, a 3.3V, low

dropout, low quiescent current linear regulator (TC1108-3.3VDB) has been included on

the board. This enables the board to operate fully from USB bus power.

All USB compliant, bus-powered devices should implement a low-power, USB

Suspend mode. This is because the USB host may, at its own discretion, halt all USB

traffic – including Start-of-Frame packets – to a USB peripheral device for more than

3 ms. When a peripheral device detects this condition, it should drop to a low-power

suspend state, so it draws no more than 2.5 mA from the +5V V

BUS supply pin.

Two USB interrupts: IDLEIF (UIR<4>) and ACTVIF (UIR<2>) are useful in detecting

when the low-power suspend condition should begin and when it actually ends.