TUSB2040A

4-PORT HUB FOR THE UNIVERSAL SERIAL BUS

WITH OPTIONAL SERIAL EEPROM INTERFACE

SLLS288B – FEBRUARY 1998 – REVISED MARCH 1998

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 three power configurations are bus-powered,

self-powered and high-powered modes. For all three configurations, 100 mA is the maximum current that may

be drawn from the USB 5-V line during power up. 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 its own power supply and can supply

up to 500 mA to each downstream port. High-powered functions may draw a maximum of 500 mA and may only

be connected downstream to self-powered hubs.

Both bus-powered and self-powered hubs require overcurrent 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 overcurrent condition, the USB host

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 overcurrent condition on any of the downstream ports,

all the ganged ports are disabled by the USB host.

Using a combination of the BUSPWR and GANGED inputs, the TUSB2040A 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 TUSB2040A, the

needed to implement a fully USB Specification 1.0 compliant system.