USB3320 datasheet(29/70 Pages) MICROCHIP

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DS00001792B-page 29

USB3320

rupt Enable Rising and USB Interrupt Enable Falling registers. When the interrupts are disabled, the SessVld compar-

ator is not disabled and its state can be read in the USB Interrupt Status register. The SessVld comparator trip point is

detailed in Table 4-7.

5.6.2.3

VbusVld Comparator

The final VBUS comparator is the VbusVld comparator. This comparator is only used when the USB3320 is configured

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

within a specified voltage range. The VbusVld 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 VbusVld comparator trip points are detailed in Table 4-7.

The internal VbusValid comparator is designed to ensure the VBUS voltage remains above 4.4V.

The USB3320 includes the external vbus valid indicator logic as detail in the ULPI Specification. The external vbus valid

indicator is tied to a logic one. The decoding of this logic is shown in Table 5-6 below. By default this logic is disabled.

Note 5-3

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.

5.6.2.4

VBUS Pulsing with Pull-up and Pull-down Resistors

In addition to the internal VBUS comparators, the USB3320 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 USB3320 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.

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 Overvoltage 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 USB3320 provides a 75kΩ resistance to ground, RVB. The RVB

resistor tolerance is detailed in Table 4-7.

Note:

The OTG Supplement specifies a voltage range for A-Device Session Valid and B-Device Session Valid

comparator. The USB3320 transceiver combines the two comparators into one and uses the narrower

threshold range.

TABLE 5-6:

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)

Fixed 1

Fixed 0

Internal VbusVld comparator.

Fixed 0

Standard Host

Fixed 1

Fixed 0

Standard

Peripheral

Internal VbusVld comparator. This

information should not be used by the Link.

(Note 5-3)

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