USB6B1

Technical information

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2.3

Universal Serial Bus

The data transmission standard, Universal Serial Bus (USB) is being driven by market

leaders in the world of Computer and Telecommunications, including Compaq, DEC,

IBM, Intel, Microsoft, NEC and Nortel, and has become a leading transmission protocol.

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 use USB ports.

The USB offers high speed communication rates up to 480 Mbit/s. Only two wires (D+, D-)

are required for data transfer. Additionally, limited amount of power for USB devices located

on the downstream can also be transmitted on two separate conductors within the same

cable.

2.4

Protection to support USB

Designers dealing with the USB chips are concerned 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

conventional 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.

Figure 6.

Recommended configuration for USB port protection

The capacitance between the I/O transmission wires provides no significant signal distortion

at the 12 Mbit/s data rate, thus allowing compatibility with USB standard.

Available in a compact SO-8 this protective element requires minimal board space and

eases the PCB layout thanks to its direct compatibility with the USB connector pin-out.

1

USB

IC

D+

D-

GND

USB output

connector