USB3320 Datasheet, PDF (28/70 Pages) Microchip Technology – Highly Integrated Full Featured Hi-Speed USB 2.0 ULPI Transceiver

USB3320
5.6.2 VBUS MONITOR AND PULSING
The USB3320 includes all of the VBUS comparators required for OTG. The VBUSVld, SessVld, and SessEnd compar-
ators shown in Figure 5-11 are fully integrated into the USB3320. These comparators are used to monitor changes in
the VBUS voltage, and the state of each comparator can be read from the USB Interrupt Status register.
The VbusVld comparator is used by the Link, when configured as an A device, to ensure that the VBUS voltage on the
cable is valid. The SessVld comparator is used by the Link when configured as both an A or B device to indicate a ses-
sion is requested or valid. Finally the SessEnd comparator is used by the B-device to indicate a USB session has ended.
Also included in the VBUS Monitor and Pulsing block are the resistors used for VBUS pulsing in SRP. The resistors used
for VBUS pulsing include a pull-down to ground and a pull-up to VDD33.
In some applications, voltages much greater than 5.5V may be present at the VBUS pin of the USB connector. The
USB3320 includes an overvoltage protection circuit that protects the VBUS pin of the USB3320 from excessive voltages
as described in Section 5.6.2.6, and shown in Figure 5-11.
FIGURE 5-11:
USB3320 OTG VBUS BLOCK
VDD33
VBUS
To USB Con. _RVBUS
VBUS
Overvoltage
Protection
ChrgVbus
0.5V
SessEnd
en
SessEnd Rise or
SessEnd Fall
SessValid
1.4V
DischrgVbus
4.575V
VbusValid
en
VbusValid Rise or
VbusValid Fall
EXTVBUS (logic 1)
IndicatorComplement
[0, X]
[1, 0]
[1, 1]
[UseExternalVbusindicator, IndicatorPassThru]
PHY
RXCMD VbusValid
5.6.2.1 SessEnd Comparator
The SessEnd comparator is designed to trip when VBUS is less than 0.5 volts. When VBUS goes below 0.5 volts the
USB session is considered to be ended, and SessEnd will transition from 0 to 1. The SessEnd comparator can be dis-
abled by clearing this bit in both the USB Interrupt Enable Rising and USB Interrupt Enable Falling registers. When dis-
abled, the SessEnd bit in the USB Interrupt Status register will read 0. The SessEnd comparator trip points are detailed
in Table 4-7.
5.6.2.2 SessVld Comparator
The SessVld comparator is used when the transceiver is configured as both an A and B device. When configured as an
A device, the SessVld is used to detect Session Request protocol (SRP). When configured as a B device, SessVld is
used to detect the presence of VBUS. The SessVld interrupts can be disabled by clearing this bit in both the USB Inter-
DS00001792B-page 28
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