USB3500 datasheet(29/46 Pages) SMSC

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Hi-Speed USB Host, Device or OTG PHY With UTMI+ Interface

Datasheet

SMSC USB3500

Revision 1.0 (04-04-05)

DATASHEET

6.7.1

ID Detection

The USB3500 provides an ID pin to determine the type of USB cable connected. When the Mini-A

Plug of a USB cable is inserted into the Mini-AB connector, the ID pin is shorted to ground. When the

Mini-B Plug is inserted into the Mini-AB connector, the ID pin is allowed to float.

The USB3500 provides an integrated pull-up resistor to pull the ID pin to VDD3.3 when a Mini-B plug

is inserted and the cable is floating. When a Mini-A plug is connected, the pull-up resistor will be

overpowered and the ID pin will be brought to ground. To save current when a Mini-A Plug is inserted,

the ID pull-up resistor can be disabled by clearing the IDPULLUP pin. 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 6.8 and their related parameters are shown in Table 5.7.

6.7.2

VBUS Control

The USB3500 includes all of the Vbus comparators required for OTG. The VbusVld, SessVld, and

SessEnd comparators are fully integrated into the USB3500. 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 either

an A or B device to indicate a session 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.

6.7.2.1

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 session is considered to be ended and SessEnd will transition from 0 to 1. The SessEnd

comparator is disabled when the Suspendn = 0. When disabled, the SessEnd output is 0. The

SessEnd comparator trip points are detailed in Table 5.7.

6.7.2.2

SessVld Comparator

The SessVld comparator is used when the PHY is configured as either an A or 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 comparator

is not disabled with Suspendn and its output will always reflect the state of VBUS. The SessVld

comparator trip point is detailed in Table 5.7.

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

Session Valid comparator. The USB3500 PHY combines the two comparators into one and

uses the narrower threshold range.

6.7.2.3

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 is disabled when Suspendn = 0. When disabled the

VbusVld will read 0. The VbusVld comparator trip points are detailed in Table 5.7.

Table 6.2 IdGnd vs. USB Cable Type

USB PLUG

OTG ROLE

ID VOLTAGE

IDGND

AHOST

PERIPHERAL

3.3

USB3500 Datasheet(PDF) 29 Page - SMSC Corporation

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