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AN1826

APPLICATION NOTE

®

TRANSIENT PROTECTION SOLUTIONS:

Transil™ diode versus Varistor

AN1826/0104

A. BREMOND / C. KAROUI

Since the seventies, electronic modules are more and more present in our life. This is the case for our

entertainment, automotive, telecommunication, production tools, house access equipment, and it is not

really a secret that these smart functions are very sensitive to transients coming from human body itself

(ESD

These surges are more often lethal for the electronic functions and the constant decrease of silicon

elementary cell size (transistor) makes them more and more compact but more and more fragile.

To assume a correct definition of a protection stage, we have to ask the two following questions :

- what we have to protect?

- against what we have to be protected?

The answer to the first question depends on both the technology used to realize the part to be protected

and normal operating waveform of the signal on the line to be protected. Needed parameters are the

the second one is closely linked to the environment where modules are operating. In each application we

have to focus on one type of disturbances, i.e. in telecom we are faced to atmospheric effects, in domestic

and industrial worlds, disturbances are EOS while in computer or mobile phones, the main surge cause is

due to ESD.

To avoid dramatic consequences on systems submitted to over voltage transients, the best way is to use

protection devices based on clamping action.

In this kind of products we have the choice between two technologies :

- silicon devices named Transil™ - so called TVS

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- and ceramic components - Varistor for instance.

V

I

Fig. 1: Electrical characteristics of bi-directional

clamping devices.

clamping device, this curve has two areas.

the normal operating zone; in this area the signal is

not be affected by the transient suppressor (low

leakage current and negligible intrinsic capacitance).

The second one is the surge suppression zone in

which the surge is clamped at VCL

VV

R

I

CL

BR

d

PP

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