USB3300 datasheet(38/53 Pages) MICROCHIP

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USB3300

DS00001783B-page 38

 2014-2015 Microchip Technology Inc.

6.5.2.5

Vbus Input Impedance

The OTG Supplement requires an A-Device that supports Session request protocol to have an input impedance less

than 100kohm and greater the 40kohm to ground. In addition, if configured as a B-Device, the PHY cannot draw more

then 150uA from Vbus. The USB3300 provides a 75kΩ nominal resistance to ground which meets the above require-

ments, see Table 5-6.

6.5.3

DRIVING EXTERNAL VBUS

When a system is operating as a host, it is required to source 5 volts on VBUS. The USB3300 fully supports VBUS

power control using external devices. The USB3300 provides an active high control signal, CPEN, which is dedicated

to controlling the Vbus supply when configured as an A-Device. The USB3300 also supports external Vbus fault detec-

tion detailed in Section 6.5.4.

CPEN is asserted when the ULPI OTG Control register bit 5 DrvVbus or bit 6, DrvVbusExternal is set high. To be com-

patible 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 6-10, "USB3300 On-the-Go Module". DrvVbus and DrvVbusExternal are set to 0

on POR.

6.5.4

EXTERNAL VBUS INDICATOR

The USB3300 has fully implemented the External Vbus detection described in the ULPI 1.1 specification. The block dia-

gram of the External Vbus detection is shown in Figure 6-10 and in Table 6-10.

Note 6-1

Microchip does not recommend using the ExternalVbus signal qualified with the internal VbusVld

comparator.

Note 6-2

A peripheral should not use VbusVld to begin operation. The peripheral should use SessVld because

the internal VbusVld threshold can be above the Vbus voltage required for USB peripheral operation.

A host PHY may use an active high or low fault by setting the IndicatorComplement bit [5] in the Interface Control reg-

ister. Also this implementation supports the IndicatorPassThru bit [6] in the Interface Control register, which allows a

choice of having the External Vbus input qualified (and’ed) with the external vbus comparator output. To use the External

Vbus Input the UseExternalVbusIndicator bit [7] must be set in the OTG control register. The default is not to use this

input.

The EXTVBUS pin has a built in pull down resistor that is controlled by the UseExternalVbusIndicator bit [7] of the OTG

control register. When UseExternalVbusIndicator is set to 0 (default) the pull down resistor is activated to prevent the

pin from floating when it is unused. When UseExternalVbusIndicator is set to 1 the pull down resistor is disconnected.

TABLE 6-10:

EXTERNAL VBUS INDICATOR LOGIC

Typical

Application

Use External

VBus Indicator

Indicator Pass

Thru

Indicator

Complement

RXCMD Vbus Valid

Encoding Source

OTG Device

Internal VbusVld comparator (Default)

External active high VbusVld signal

External active low VbusVld signal

External active high power fault signal

qualified with internal VbusVld comparator.

(Note 6-1)

External active low power fault signal

qualified with internal VbusVld comparator.

(Note 6-1)

Standard Host

External active high power fault signal

External active low power fault signal

Standard

Peripheral

Internal VbusVld comparator. This should

not be used by the Link. (Note 6-2)

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