Part # Application Note Computer And Peripherals ST1394 Emi Filtering datasheet

Part Manufacturer: ST Microelectronics

ST Microelectronics


Part Details:

AN1783 ® APPLICATION NOTE HOW TO MAKE FIRE-WIRE COMMUNICATION PORT SAFE? P. MERCERON Video-media equipment growth has lead manufacturers to use fast transmission buses in order to share in-formation quickly and easily. In many cases, video equipment use Fire-Wire link (IEEE1394) which brings the following features: n Up to 63 devices can be plugged on the bus n 400Mb/s data transmission rate n Hot plugging n Power through the cable n Plug-and-play n Low cost cabling n Low implementation cost As a matter of fact, this race for fast transmission and small compact video machines (cameras, mobiles,video equipment) has brought more and more integrated and sensitive electronic devices at the same time.As a result, on one hand, protection devices have been required to make the system more robust regardingESD while, on the other hand, line adaptation have been implemented to prevent fast signal distortion dueto high data rate transmission across non ideal elements. ST1394-01SC6 is one of those devices that com- Fig. 1: ST1394-01SC6 internal diagram. bine both ESD protection and line termination at atime in one chip especially designed for Fire-Wiretransmission. Its ± 4kV ESD IEC61000-4-2 compliance andsmall package (1.5x2.8mm) makes it very conve-nient for IEEE1394 link. The following internal diagram gives an idea of itscharacteristics. We can notice on figure 1 the following points: n ESD protection is performed with clampingdiodes located at each line side. n RC elements realize line termination at eachdata lines n Moreover, intrinsic clamping diode capacitorsoffers RF rejection for GSM bandwidth. October 2003 - Ed: 1 1/9 AN1783 - APPLICATION NOTE ST1394-01SC6 BOARD PLACEMENT RECOMMANDATIONS Whatever the protection device at Fire Wire connector, it is known that upon ESD strike occurrence, a re-maining over voltage is applied at sensitive IC side. In main cases a small part of this over voltage is com-ing from the clamping of the protection diode and a larger part from the copper track that connectscomponent altogether. For this reason it is important also to focus on the way component are routed. The way the ST1394-01SC6 is mounted on the Fire-Wire communication printed board is also a major con-cern. This will affect the ESD and line termination efficiency. Keep in mind when facing +4kV ESD surge(IEC61000-4-2, level 2), a 10mm long; 0,5mn wide; 35µm thick copper track will induce about 70V!!over-voltage due to track parasitic inductance. Indeed, fast di/dt induced by the ESD IEC61000-4-2 level 2 brings the following calculation: n The ESD surge has a step rise time of 0.7ns minimum. n The level 2 of the ESD test table stands for 4kV air discharge and the internal series resistance of theequivalent ESD generator is 330 ohms, thus the peak current induced by the 4kV surge is roughly 12A n A 1mm, 35µm thick, 0.5mm wide is 0.4nH Then considering a 10mm; 35µm; 0.5mm copper track, the voltage drop along this track comes up with: dI 9 12 1 . V = L ; then it isV = 10 × 0 4

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