Microchip Technology MPLAB Starter Kit for PIC18F MCU DM180021 DM180021 Manuel D’Utilisation
Codes de produits
DM180021
USB Current Draw Requirements
© 2009 Microchip Technology Inc.
DS51852A-page 37
B.4
USB SUSPEND CURRENT LIMITATIONS FOR THE STARTER KIT
The USB specification limits devices to 2.5 mA of current draw from the bus while a
device is in a suspended state. This limit is tested during compliance testing for all USB
certified devices.
device is in a suspended state. This limit is tested during compliance testing for all USB
certified devices.
The design of the PIC18F Starter Kit utilizes an on-board debugger. To optimize the
starter kit for cost and available features, the debugger section provides the system
clock for both the debugger and the application portions of the circuit. As a result, the
debugger is always running, even when the debugger USB cable is not attached,
resulting in a current draw higher than allowed during USB suspend. In contrast, typical
applications will have their own clock sources and be able to better control their own
current consumption to meet the USB suspend specification. This can be achieved by
switching to a lower clock frequency or placing the microcontroller into Sleep mode,
among other possible methods.
starter kit for cost and available features, the debugger section provides the system
clock for both the debugger and the application portions of the circuit. As a result, the
debugger is always running, even when the debugger USB cable is not attached,
resulting in a current draw higher than allowed during USB suspend. In contrast, typical
applications will have their own clock sources and be able to better control their own
current consumption to meet the USB suspend specification. This can be achieved by
switching to a lower clock frequency or placing the microcontroller into Sleep mode,
among other possible methods.