AN2689 datasheet(10/42 Pages) STMICROELECTRONICS

10 / 42 page

Data line protection

AN2689

10/42

Doc ID 14310 Rev 3

This topology is easy to manage. There should be as many protection devices as there are

lines to protect. The protection device in fact can be several single Transils but there is a

possibility to use protection devices in an array package so that one device protects each

data line as shown in Figure 9.

Figure 9.

Data line protection using a diode array

This clamping topology is good when the clamping voltage of each Transil is close to the

nominal voltage of the data lines to be protected. For example, if the nominal voltage is 5 V,

an ESDA6V1xx (Vbr = 6.1 V) protection device is ideal. The Transil offers a fixed clamping

voltage which does not require external power supply as in the rail-to-rail configuration but

for some cases it is more convenient to use the rail-to-rail topology as described below.

3.1.2

Rail-to-rail topology

The rail-to-rail topology, shown in Figure 10, is achieved using simple regular diodes. In that

case the clamping level is no longer fixed but, instead, depends on the power supply voltage

Vcc. As soon as a surge occurs, all the voltage over Vcc is diverted to the power supply as

shown in Figure 11.

In this case the remaining over voltage that the data line is exposed to is very low.

Figure 10.

Rail-to-rail protection topology

Module to protect

Vnom

Vmax

Transil array

Vcc

Module to protect

Vnom

Vmax

Vcc

AN2689 Datasheet(PDF) 10 Page - STMicroelectronics