USB3300 datasheet(37/53 Pages) MICROCHIP

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DS00001783B-page 37

USB3300

bit in the OTG Control register. To prevent the ID pin from floating to a random value, a weak pull-up resistor is provided

at all times. The circuits related to the ID comparator are shown in Figure 6-10, "USB3300 On-the-Go Module" and their

related parameters are shown in Table 5-6, "OTG Electrical Characteristics".

The status of IdGnd can be read by reading the ULPI USB Interrupt Status register, bit 4. It can also be set to generate

an interrupt, in host mode, when IdGnd changes with the ULPI Interrupt Enable registers.

6.5.2

VBUS CONTROL

The USB3300 includes all of the Vbus comparators required for OTG. The VbusVld, SessVld, and SessEnd compara-

tors are fully integrated into the USB3300. These comparators are used to ensure the Vbus voltage is the correct value

for proper USB operation.

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 Control 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 VDD3.3.

6.5.2.1

SessEnd Comparator

The SessEnd comparator is designed to trip when Vbus is less than 0.5 volts. When Vbus goes below 0.5 volts the ses-

sion is considered to be ended and SessEnd will transition from 0 to 1. The SessEnd compatator can be disabled by

clearing this bit in both the rising and falling interrupt enable registers. When disabled the SessEnd bit in the interrupt

status register will read 0. The SessEnd comparator trip points are detailed in Table 5-6.

6.5.2.2

SessVld Comparator

The SessVld comparator is used when the PHY is configured as both an A and B device. When configured as an A

device, the SessVld is used to detect Session Request protocol (SRP). When configured as a B device, SessVld is used

to detect the presence of Vbus. The SessVld interrupts can be disabled by clearing this bit in both the rising and falling

interrupt enable registers. When the interrupts are disabled, the SessVld comparator is not disabled and its state can

be read in the interrupt status register. The SessVld comparator trip point is detailed in Table 5-6.

6.5.2.3

VbusVld Comparator

The final Vbus comparator is the VbusVld comparator. This comparator is only used when configured as an A-device.

In the OTG protocol the A-device is responsible to ensure that the Vbus voltage is within a certain range. The VbusVld

comparator can be disabled by clearing both the rising and falling edge interrupts. When disabled a read of bit 1, in the

Interrupt Status Register will return a 0. The VbusVld comparator trip points are detailed in Table 5-6.

When the A-device is able to provide 8-100mA it must ensure Vbus doesn’t go below 4.4 volts. If the A-device can pro-

vide 100-500mA on Vbus it must ensure that Vbus does not go below 4.75 volts.

The internal Vbus comparator is designed to ensure that Vbus remains above 4.4 volts. If the design is required to sup-

ply over 100mA the USB3300 provides an input for a more accurate Vbus comparator or fault (over current) detection

described in Section 6.5.4, "External Vbus Indicator".

6.5.2.4

Vbus Pull-up and Pull-down Resistors

In addition to the internal Vbus comparators the USB3300 also includes the integrated Vbus pull-up and pull-down resis-

tors used for Vbus Pulsing. To discharge the Vbus voltage, so that a Session Request can begin, the USB3300 provides

a pull-down resistor from Vbus to Ground. This resistor is controlled by the DischargeVbus bit 3 of the OTG Control

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, defined in the ULPI specifications.

The Pull-Up and Pull-Down resistor values are detailed in Table 5-6.

Note:

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

comparator. The USB3300 PHY combines the two comparators into one and uses the narrower threshold

range.

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