AN1040 Datasheet, PDF (1/4 Pages) STMicroelectronics – FOR USB SELF-POWERED DEVICES

AN1040
APPLICATION NOTE
MONITORING THE V_BUS SIGNAL
FOR USB SELF-POWERED DEVICES
by Microcontroller Division
INTRODUCTION
One of the USB Compliance Checklist for Peripherals items asks the following question: “Is
the device’s pull-up active only when V_BUS is high?”.
This item refers to chapter 7.1.5 “Device Speed Identification” of the USB Specification. It is
mentioned that “the voltage source on the pull-up resistor must be derived from or controlled
by the power supplied on the USB cable such that when V_BUS is removed, the pull-up resistor
does not supply current on the data line to which it is attached”
This applies only to self-powered devices where power does not come from V_BUS.
AN1040/1000
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