USB6Bx

4/9

Fig. A3: recommended configuration for USB port protection.

1

Vbus

D+

D-

GND

USB output

connector

USB

IC

Universal Serial Bus.

The new data transmission standard, Universal

Serial Bus (USB) is being driven by market leaders

in the world of Computer and Telecommunica-

tions,

including

Compaq,

DEC,

IBM,

Intel,

Microsoft, NEC and Nortel, and will become the

leading transmission protocol within the next few

years.

This

standard

mainly

provides

simplified

interconnectivity. Specialized ports on the back of

the present PC will largely be replaced by USB

ports. Many peripherals such as printers, key-

boards, monitors and joysticks will also host USB

ports.

The USB offers high speed communication rates

up to 12 Mbit/s. Only two wires (D+, D-) are re-

quired for data transfer. Additionally, limited

amount of power for USB devices located on the

downstream can also be transmitted on two sepa-

rate conductors within the same cable.

Protection to support USB.

Designers dealing with the USB chips are con-

cerned about electrostatic discharge sensitivity

(ESD) of their USB controller ICs.

The USB controller is more than just a driver /

receiver; it acts as a microcontroller which

manages power and direct signal traffic. This

complexity increases its cost over conven-

tional devices. Therefore, a failure of a USB

port could result in costly computer failure.

In order to prevent these fast transients from

leading to severe damages in a system, a

specific protection has been developed by

STMicroelectronics. The USB6Bx protects

not only the two wires of data transmission,

but also keep the power rails in a safe limit.

The capacitance between the I/O transmission

wires provides no significant signal distortion at the

12 Mbit/s data rate, thus allowing full compatibility

with USB standard.

Available either in a compact SO8 or in a

through-hole DIL8 package, this protective ele-

ment requires minimal board space and eases the

PCB layout thanks to its direct compatibility with

the USB connector pin-out.

TECHNICAL INFORMATION