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AN588 APPLICATION NOTE

Aware of this problem, the manufacturers of interface circuits have proposed components with auto-pro-

tected I/O’s up to 1 to 2kV. But in the case of long lines which are heavily exposed to disturbances, this

precaution is not enough and, therefore, requires the use of specific ESD protection devices.

The ITAxxB3 and ITAxxU3, which offer 8-transil functions in an SO20 package, have been especially de-

signed for this application. The internal wiring is based on a 4-point structure which allows the isolation of

the input from the output, guaranteeing a reliable protection with clamping voltages less than 30V. This

assures a real protection of the line interfaces.

In order to achieve such performance from these components, some recommendations about PCboard

mounting must be given.

Figure 3 shows what type of lay-out must be used in order to take advantage of the 4-point structure of

the ITAxxB3 and ITAxxU3. With this configuration, each data line passes through the protection device.

In this case, it acts as an interface between the cable and the circuit to be protected and guarantees an

isolation between its inputs and outputs.

The ESD wave is deviated across the input of the protection device. Therefore, the circuit to be protected

is no longer exposed to the Ldi/dt generated by the parasitic inductances of the wiring.

Figure 3. 4 - Points Structure (ITAxxB)

The ITAxx, an efficient protection against EOS

Due to their monolithic structure which allows to optimize the active surface of the silicon, these products

have a dissipation capability equal to that of discrete components. These devices can be considered as

real protection against industrial disturbances (EOS) of the 1.2/50µsec type by guaranteeing clamping

voltages at high currents well under the maximum ratings of line interface circuits.

V

i

V : Residual Overvoltage.