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MPLAB STARTER KIT FOR PIC18F
USER ’S GUIDE
Appendix B. USB Current Draw Requirements
This chapter describes the key USB specification current limits and provides a func-
tional overview of the soft start circuitry used by the MPLAB Starter Kit for PIC18F to
meet them. The appendix includes the following sections:
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USB Current Specifications
PIC18F Starter Kit Soft Start Circuitry
Soft Start Functions and Usage
Suspend Current Limitations with the Starter Kit
B.1
USB CURRENT SPECIFICATIONS
There are three major USB current specifications that the soft start circuitry addresses:
inrush current during initial plug in, total application current draw, and suspend current
limitations.
B.1.1
Inrush Current
All USB devices are required to limit their inrush draw from the bus such that there is a
capacitance change of no more than 10 μ F for the device. (Since the USB is a 5V bus,
this equates to a charge inrush of 50 μ C.) Some applications, like the OLED on the
starter kit, may cause a capacitance change of greater than 10 μ F. To meet the
specification, the application can use current management techniques to limit the
inrush current and spread the charge over a longer period of time.
B.1.2
Total Application Current Draw
USB devices are limited to 100 mA of total current draw during the enumeration phase.
The enumeration phase is the time during which the device is first attached to the bus
and when the host sends a SET_CONFIGURATION command to the device. Devices
may request for additional current by changing the bMaxPower parameter of the
configuration descriptor. The configuration descriptor can be found in the file,
usb_descriptors.c , in each of the example demos. More information about the
bMaxPower parameter and the configuration descriptor, in general, can be found in
Table 9-10 of the USB specification.
B.1.3
Suspend Current Limitations
When the USB bus is in Suspend mode, all attached USB devices are required to use
less than 2.5 mA of current draw from the bus. For applications that have features that
require more current than is allowed, there are several options available. The first is to
be a self-powered device and only draw current from the power supply. The second is
to implement a software controlled method for reducing the current to below the 2.5 mA
limit.
? 2009 Microchip Technology Inc.
DS51852A-page 33
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相关代理商/技术参数
DM1800-434MB
功能描述:射频模块 DM1800 Base Station 433.92 MHz
RoHS:否 制造商:Linx Technologies 产品:Transceiver Modules 频带:902 MHz to 928 MHz 输出功率:- 15.5 dBm to + 12.5 dBm 接口类型:UART 工作电源电压:- 0.3 VDC to + 5.5 VDC 传输供电电流:38.1 mA 接收供电电流:22.7 mA 天线连接器类型:U.FL 最大工作温度:+ 85 C 尺寸:1.15 mm x 0.63 mm x 0.131 mm
DM1800-434MN
功能描述:射频模块 DM1800 Field Node 433.92 MHz
RoHS:否 制造商:Linx Technologies 产品:Transceiver Modules 频带:902 MHz to 928 MHz 输出功率:- 15.5 dBm to + 12.5 dBm 接口类型:UART 工作电源电压:- 0.3 VDC to + 5.5 VDC 传输供电电流:38.1 mA 接收供电电流:22.7 mA 天线连接器类型:U.FL 最大工作温度:+ 85 C 尺寸:1.15 mm x 0.63 mm x 0.131 mm
DM1800-434MN-V
功能描述:射频模块 Field Node w/ Host Ser Intr 433.92 MHz
RoHS:否 制造商:Linx Technologies 产品:Transceiver Modules 频带:902 MHz to 928 MHz 输出功率:- 15.5 dBm to + 12.5 dBm 接口类型:UART 工作电源电压:- 0.3 VDC to + 5.5 VDC 传输供电电流:38.1 mA 接收供电电流:22.7 mA 天线连接器类型:U.FL 最大工作温度:+ 85 C 尺寸:1.15 mm x 0.63 mm x 0.131 mm
DM1800-434MR
功能描述:射频模块 DM1800 Network Router 433.92 MHz
RoHS:否 制造商:Linx Technologies 产品:Transceiver Modules 频带:902 MHz to 928 MHz 输出功率:- 15.5 dBm to + 12.5 dBm 接口类型:UART 工作电源电压:- 0.3 VDC to + 5.5 VDC 传输供电电流:38.1 mA 接收供电电流:22.7 mA 天线连接器类型:U.FL 最大工作温度:+ 85 C 尺寸:1.15 mm x 0.63 mm x 0.131 mm
DM1800-434MR-PAH
功能描述:射频模块 DM1800 Pkg Router 433.92 MHz Horzt Mnt
RoHS:否 制造商:Linx Technologies 产品:Transceiver Modules 频带:902 MHz to 928 MHz 输出功率:- 15.5 dBm to + 12.5 dBm 接口类型:UART 工作电源电压:- 0.3 VDC to + 5.5 VDC 传输供电电流:38.1 mA 接收供电电流:22.7 mA 天线连接器类型:U.FL 最大工作温度:+ 85 C 尺寸:1.15 mm x 0.63 mm x 0.131 mm
DM1800-434MR-PAV
功能描述:射频模块 DM1800 Pkg Router 433.92 MHz Vert Mnt
RoHS:否 制造商:Linx Technologies 产品:Transceiver Modules 频带:902 MHz to 928 MHz 输出功率:- 15.5 dBm to + 12.5 dBm 接口类型:UART 工作电源电压:- 0.3 VDC to + 5.5 VDC 传输供电电流:38.1 mA 接收供电电流:22.7 mA 天线连接器类型:U.FL 最大工作温度:+ 85 C 尺寸:1.15 mm x 0.63 mm x 0.131 mm
DM1800-434MR-PBH
功能描述:射频模块 DM1800 Pkg Router 433.92 MHz Horzt Mnt
RoHS:否 制造商:Linx Technologies 产品:Transceiver Modules 频带:902 MHz to 928 MHz 输出功率:- 15.5 dBm to + 12.5 dBm 接口类型:UART 工作电源电压:- 0.3 VDC to + 5.5 VDC 传输供电电流:38.1 mA 接收供电电流:22.7 mA 天线连接器类型:U.FL 最大工作温度:+ 85 C 尺寸:1.15 mm x 0.63 mm x 0.131 mm
DM1800-434MR-PBV
功能描述:射频模块 DM1800 Pkg Router 433.92 MHz Vert Mnt
RoHS:否 制造商:Linx Technologies 产品:Transceiver Modules 频带:902 MHz to 928 MHz 输出功率:- 15.5 dBm to + 12.5 dBm 接口类型:UART 工作电源电压:- 0.3 VDC to + 5.5 VDC 传输供电电流:38.1 mA 接收供电电流:22.7 mA 天线连接器类型:U.FL 最大工作温度:+ 85 C 尺寸:1.15 mm x 0.63 mm x 0.131 mm