TUSB2046A

4-PORT HUB FOR THE UNIVERSAL SERIAL BUS

WITH OPTIONAL SERIAL EEPROM INTERFACE

SLLS404 – DECEMBER 1999

8

POST OFFICE BOX 655303

APPLICATION INFORMATION

A major advantage of USB is the ability to connect 127 functions configured in up to six logical layers (tiers) to

a single personal computer (see Figure 5).

Figure 5. USB Tiered Configuration Example

PC

With Root Hub

Monitor

With 4-Port Hub (Self-Powered)

Keyboard

With 4-Port Hub

(Bus-Powered)

Printer

With 4-Port Hub

(Self-Powered)

Modem

Telephone

Mouse

Left

Speaker

Right

Speaker

Digital

Scanner

Scanner

Another advantage of USB is that all peripherals are connected using a standardized four-wire cable that

provides both communication and power distribution. The power configurations are bus-powered and

self-powered modes. The maximum current that may be drawn from the USB 5-V line during power up is

100 mA. For the bus-powered mode, a hub can draw a maximum of 500 mA from the 5-V line of the USB cable.

A bus-powered hub must always be connected downstream to a self-powered hub unless it is the only hub

connected to the PC and there are no high-powered functions connected downstream. In the self-powered

mode, the hub is connected to an external power supply and can supply up to 500 mA to each downstream port.

High-powered functions may draw a maximum of 500 mA from each downstream port and may only be

connected downstream to self-powered hubs. Per the USB specification, in the bus-powered mode, each

downstream port can provide a maximum of 100 mA of current, and in the self-powered mode, each

downstream port can provide a maximum of 500 mA of current.

Both bus-powered and self-powered hubs require over-current protection for all downstream ports. The two

types of protection are individual port management (individual port basis) or ganged port management (multiple

port basis). Individual port management requires power management devices for each individual downstream

port, but adds robustness to the USB system because, in the event of an over-current condition, the USB host

only powers down the port that has the condition. The ganged configuration uses fewer power management

devices and thus has lower system costs, but in the event of an over-current condition on any of the downstream

ports, all the ganged ports are disabled by the USB host.

Using a combination of the BUSPWR and EEDATA/GANGED inputs, the TUSB2046A supports four modes of

power management: bus-powered hub with either individual port power management or ganged port power

management, and the self-powered hub with either individual port power management or ganged port power

management. Texas Instruments supplies the complete hub solution because we offer this TUSB2046A, the

needed to implement a fully USB Specification 1.1 compliant system.