USB334X datasheet(35/92 Pages) MICROCHIP

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DS00002646A-page 35

USB334x

5.7.2

VBUS MONITORING AND VBUS PULSING

The USB334x includes all of the VBUS comparators required for OTG. The VBUSVld, SessVld, and SessEnd compar-

ators shown in Figure 5-8 are fully integrated into the USB334x. 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

USB334x includes an over voltage protection circuit that protects the VBUS pin of the USB334x from excessive voltages

as shown in Figure 5-8.

5.7.2.1

SessEnd Comparator

The SessEnd comparator is used during the Session Request Protocol (SRP). The comparator is used by the B-device

to detect when a USB session has ended and it is safe to start Vbus Pulsing to request a USB session from the A-device.

When VBUS goes below the threshold in Table 4-8, the USB session is considered to be ended, and SessEnd will tran-

sition from 0 to 1. The SessEnd comparator can be disabled by clearing this bit in both the USB Interrupt Enable Rising

and USB Interrupt Enable Falling registers. When disabled, the SessEnd bit in the USB Interrupt Status register will read

Note:

The IdGnd switch has been provided to ground the ID pin for future applications.

FIGURE 5-8:

USB334X OTG VBUS BLOCK

VbusValid

SessValid

SessEnd

DischrgVbus

0.5V

1.4V

4.575V

VBUS

VDD33

MCHP 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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