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
V
BUS
D+
D-
GND
USB output
connector
