USB3317C_V01 datasheet(32/76 Pages) SMSC

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Hi-Speed USB Transceiver with 1.8V-3.3V ULPI Interface - 26MHz Reference Clock

Datasheet

Revision 2.1 (06-02-10)

SMSC USB3317 REV C

DATASHEET

5.6.2.4

Vbus Pulsing with Pull-up and Pull-down Resistors

In addition to the internal Vbus comparators, the USB3317 also includes the integrated Vbus pull-up

and pull-down resistors used for Vbus Pulsing. To discharge the Vbus voltage so that a Session

Request can begin, the USB3317 provides a pull-down resistor from Vbus to Ground. This resistor is

controlled by the DischargeVbus bit 3 of the OTG Control register. The pull-up resistor is connected

between Vbus and VDD33. This resistor is used to pull Vbus above 2.1 volts so that the A-Device

knows that a USB session has been requested. The state of the pull-up resistor is controlled by the

bit 4 ChargeVbus of the OTG Control register. The Pull-Up and Pull-Down resistor values are detailed

in Table 4.7.

5.6.2.5

Vbus Input Impedance

The OTG Supplement requires an A-Device that supports Session Request Protocol to have a VBUS

input impedance less than 100kΩ and greater the 40kΩ to ground. The USB3317 provides a 75kΩ

resistance to ground, RVB. The RVB resistor tolerance is detailed in Table 4.7.

5.6.3

Driving External Vbus

A system that is operating as a host is required to source 5 volts on VBUS. The USB3317 fully

supports VBUS power control using external devices. The USB3317 provides an active high control

signal, CPEN, which is dedicated to controlling the Vbus supply when configured as an A-Device.

CPEN is asserted by setting the DrvVbus or DrvVbusExternal bit of the OTG Control register. To be

compatible with Link designs that support both internal and external Vbus supplies the DrvVbus and

DrvVbusExternal bits in the OTG Control Register are or’d together. This enables the Link to set either

bit to access the external Vbus enable (CPEN.) This logic is shown in Figure 5.9. DrvVbus and

DrvVbusExternal are set to 0 on POR.

Figure 5.9 USB3317 Drives External Vbus Supply or Switch

PHY

REFCLK

USB

Connector

D-

D+

VBUS

ULPI Bus

SOC/FPGA/ASIC

REFCLK

ULPI Bus

DrvVbusExternal

DrvVbus

CPEN

VBUS

Supply

or Switch

Out

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