Philips ISP1122 6. Functional description

Philips Semiconductors ISP1122

USB stand-alone hub

Product speciﬁcation Rev. 03 — 29 March 2000 8 of 48

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

[2] The voltage at pin Vreg(3.3) is gated by theRESET 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] SeeTable 4 “Mode selection”.

[4] Todisable a downstreampor t connect both D+and D−to VCC via a 1 MΩresistor; unused ports must

be disabled in reverse order starting from port 5.

[5] Analog detection circuit can be switched off using an external EEPROM, seeTab le 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 downstreampor t 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.

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

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

Table 3: Pin description for LQFP32

…continued

Symbol[1] Pin Type Description