ST STM32F103 series Reference Manual

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RM0008 USB on-the-go full-speed (OTG_FS)
957
Figure 305. USB host-only connection
1. STMPS2141STR needed only if the application has to support a V
BUS
powered device. A basic power
switch can be used if 5 V are available on the application board.
28.6.1 SRP-capable host
SRP support is available through the SRP capable bit in the global USB configuration
register (SRPCAP bit in OTG_FS_GUSBCFG). With the SRP feature enabled, the host can
save power by switching off the V
BUS
power while the USB session is suspended.
The SRP host mode program model is described in detail in the A-device session request
protocol) section.
28.6.2 USB host states
Host port power
On-chip 5 V V
BUS
generation is not supported. For this reason, a charge pump or, if 5 V are
available on the application board, a basic power switch, must be added externally to drive
the 5 V V
BUS
line. The external charge pump can be driven by any GPIO output. When the
application decides to power on V
BUS
using the chosen GPIO, it must also set the port
power bit in the host port control and status register (PPWR bit in OTG_FS_HPRT).
V
BUS
valid
When HNP or SRP is enabled the VBUS sensing pin (PA9) pin should be connected to
V
BUS
. The V
BUS
input ensures that valid V
BUS
levels are supplied by the charge pump
during USB operations. Any unforeseen V
BUS
voltage drop below the V
BUS
valid threshold
(4.25 V) leads to an OTG interrupt triggered by the session end detected bit (SEDET bit in
OTG_FS_GOTGINT). The application is then required to remove the V
BUS
power and clear
the port power bit.
When HNP and SRP are both disabled, the VBUS sensing pin (PA9) should not be
connected to V
BUS
. This pin can be can be used as GPIO.
The charge pump overcurrent flag can also be used to prevent electrical damage. Connect
the overcurrent flag output from the charge pump to any GPIO input and configure it to
generate a port interrupt on the active level. The overcurrent ISR must promptly disable the
V
BUS
generation and clear the port power bit.
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ST STM32F103 series Specifications

General

Brand	ST
Model	STM32F103 series
Category	Microcontrollers
Language	English