Board Hardware
©
2009 Microchip Technology Inc.
DS51806A-page 10
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 pr5V (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.
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