USB Current Draw Requirements
©
2009 Microchip Technology Inc.
DS51852A-page 35
FIGURE B-2:
VARYING PWM OUTPUT TO SLOWLY CROSS THE LINEAR
REGION OF Q1’S OUTPUT
FIGURE B-3:
THE ENTIRE SOFT START PROCESS
B.3
SOFT START FUNCTIONS AND USAGE
A software component on the microcontroller side is also required to manage the PWM
output and control the external circuit. The demo applications supplied with the starter
kit use three different software function calls to manage USB-related power consump-
tion.This section describes the functions provided and how they are used to meet the
USB requirements.
B.3.1
AppPowerEnable()
The
AppPowerEnable()
function starts the soft start sequence. The function initial-
izes the port pins, timers and PWM modules to get ready for the soft start. It is optional
if
APP_POWER_AUTO_ENABLE
is defined.
In light of the Total Application Current Draw specification of 100 mA, this function
should not be called until after the device is enumerated. See the following section for
more details.
Summary of Contents for MPLAB
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