USB333X datasheet(35/85 Pages) MICROCHIP

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DS00001880A-page 35

USB333x

5.6.2.3

VbusValid Comparator

The VbusValid comparator is only used when the USB333x is configured as a host that can supply less than 100mA

VBUS current. In the USB protocol, the A-device supplies the VBUS voltage and is responsible to ensure it remains

within a specified voltage range. The VbusValid comparator can be disabled by clearing this bit in both the USB Interrupt

Enable Rising and USB Interrupt Enable Falling registers. When disabled, bit 1 of the USB Interrupt Status register will

return a 0. The VbusValid comparator threshold values are detailed in Table 4-9.

If the USB333x is used as a Device only the VbusValid Comparator should be disabled, using the method described

above.

The USB333x includes the external VbusValid indicator logic as detailed in the ULPI Specification. The external

VbusValid indicator is tied to a logic one. The decoding of this logic is shown in Table 5-7 below. By default this logic is

disabled.

Note 5-4

A peripheral should not use VbusValid to detect a USB connection and begin operation. The

peripheral should use SessValid to detect the presence of VBUS on the USB connector. VbusValid

should only be used for USB Host and OTG A-device applications.

5.6.2.4

VBUS Pulsing with Pull-up and Pull-down Resistors

In addition to the internal VBUS comparators, the USB333x also includes the integrated VBUS pull-up and pull-down

resistors used for VBUS Pulsing during OTG Session Request Protocol. To discharge the VBUS voltage so that a Ses-

sion Request can begin, the USB333x provides a pull-down resistor from VBUS to GND. 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 4-9.

The internal VBUS Pull-up and Pull-down resistors are designed to include the RVBUS external resistor in series. This

external resistor is used by the VBUS Over voltage protection described below.

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 USB333x provides a 75kΩ resistance to ground, RVB. The RVB

resistor tolerance is detailed in Table 4-9.

5.6.2.6

VBUS Over Voltage Protection (OVP)

The USB333x provides an integrated over voltage protection circuit to protect the VBUS pin from excessive voltages

that may be present at the USB connector. The over voltage protection circuit works with an external resistor (RVBUS)

by drawing current across the resistor to reduce the voltage at the VBUS pin.

When voltage at the VBUS pin exceeds 5.5V, the Over voltage Protection block will sink current to ground until VBUS

is below 5.5V. The current drops the excess voltage across RVBUS and protects the USB333x VBUS pin. The required

RVBUS value is dependent on the operating mode of the USB333x as shown in Table 5-8.

TABLE 5-7:

EXTERNAL VBUS INDICATOR LOGIC

Typical

Application

Use External

VBus Indicator

Indicator

Pass Thru

Indicator

Complement

RXCMD VBUSVALID

Encoding Source

OTG Device

Internal VbusValid comparator (Default)

Fixed 1

Fixed 0

Internal VbusValid comparator.

Fixed 0

Standard Host

Fixed 1

Fixed 0

Standard

Peripheral

Internal VbusValid comparator. This

information should not be used by the Link.

(Note 5-4)

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