USB3320 datasheet(28/70 Pages) MICROCHIP

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USB3320

DS00001792B-page 28

 2014-2015 Microchip Technology Inc.

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.

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-

FIGURE 5-11:

USB3320 OTG VBUS BLOCK

VbusValid

SessValid

SessEnd

DischrgVbus

0.5V

1.4V

4.575V

VBUS

VDD33

PHY

To USB Con.

SessEnd Rise or

SessEnd Fall

VbusValid Rise or

VbusValid Fall

RXCMD VbusValid

IndicatorComplement

[UseExternalVbusindicator, IndicatorPassThru]

[0, X]

[1, 0]

[1, 1]

EXTVBUS (logic 1)

ChrgVbus

VBUS

Overvoltage

Protection

RVBUS

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