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ISP1122

Universal Serial Bus stand-alone hub

Philips Electronics 

Philips Semiconductors

ISP1122

USB stand-alone hub

Table 3: Pin description for LQFP32…continued

Symbol [1]

Pin Type Description

DM2

26 AI/O downstream port 2 D− connection (analog) [6]

DP2

27 AI/O downstream port 2 D+ connection (analog) [6]

PSW1/GL1 [3] 28 O

modes 4 to 6: power switch control output for downstream

port 1 (open-drain, 6 mA)

modes 0 to 3, 7: GoodLink LED indicator output for

downstream port 1 (open-drain, 6 mA); to connect an LED

use a 330 Ω series resistor

[1] Symbol names with an overscore (e.g. NAME) indicate active LOW signals.

[2] The voltage at pin Vreg(3.3) is gated by the RESET pin. This allows fully self-powered operation by

connecting RESET to VBUS (+5 V USB supply). If VBUS is lost upstream port D+ will not be driven.

[3] See Table 4 “Mode selection”.

[4] To disable a downstream port connect both D+ and D− to VCC via a 1 MΩ resistor; unused ports must

be disabled in reverse order starting from port 5.

[5] Analog detection circuit can be switched off using an external EEPROM, see Table 23; in this case,

the pin functions as a logic input (TTL level).

[6] Downstream ports 1 and 2 cannot be disabled.

6. Functional description

The ISP1122 is a stand-alone USB hub with up to 5 downstream ports. The number

of ports can be configured between 2 and 5. The downstream ports can be used to

connect low-speed or full-speed USB peripherals. All standard USB requests from

the host are handled by the hardware without the need for firmware intervention. The

block diagram is shown in Figure 1.

The ISP1122 requires only a single supply voltage. An internal 3.3 V regulator

provides the supply voltage for the analog USB data transceivers.

The ISP1122 supports both bus-powered and self-powered hub operation. When

using bus-powered operation a downstream port cannot supply more than 100 mA to

a peripheral. In case of self-powered operation an external supply is used to power

the downstream ports, allowing a current consumption of max. 500 mA per port.

A basic I2C-bus interface is provided for reading vendor ID, product ID and

configuration bits from an external EEPROM upon a reset.

6.1 Analog transceivers

The integrated transceiver interfaces directly to the USB cables through external

termination resistors. They are capable of transmitting and receiving serial data at

both ‘full-speed’ (12 Mbit/s) and ‘low-speed’ (1.5 Mbit/s) data rates. The slew rates

are adjusted according to the speed of the device connected and lie within the range

mentioned in the USB Specification Rev. 1.1.

9397 750 07002

Product specification

Rev. 03 — 29 March 2000

© Philips Electronics N.V. 2000. All rights reserved.

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