AN588 APPLICATION NOTE

2/12

STMicroelectronics’ objective in developing this range of Transil arrays (ITAxxx) was to propose solutions

that correspond exactly to these demands (see Annex 2: Protection Standards Applicable to Computer

and Electronic Systems). These components are designed in order to protect against over-voltages result-

ing from ESD or EOS that disturb data transmission lines and for which the characteristics are stated be-

low:

– ESD discharges have very little energy. However, they are very rapid (5/30ns waves) and present very

high voltage peaks, around 15KV. The component must assure an efficient protection in dynamic

transients with rise times such as 10A/ns. In this case, the performance of the protection device is not

linked to the silicon but to the structure of the connections and the track lay-out of the PC board.

– The EOS are longer over-voltages (1.2/50µs waves) with voltage peaks of 500V to 1KV. Because these

disturbances are powerful, the protection device must be able to dissipate the power in the silicon in

order to guarantee low clamping voltage levels.

ITAxx, a reliable protection against ESD

It has been shown that in the presence of ESD-type disturbances, standard protection devices (axial and

even SMD diodes) only guarantee a protection level of about a few hundred volts. We still find at the lead

an over-voltage created by the parasitic inductances (Ldi/dt) which can reach several hundreds of volts.

Figure 2 illustrates this behavior.

Figure 2. Protection Against ESD

DEVICE

TO BE

PROTECTED

i

LINE

DEVICE

TO BE

PROTECTED

i

LINE

V

LL

V CL

CONVENTIONAL PROTECTION.

EQUIVALENT CIRCUIT IN DYNAMIC

BEHAVIOUR.

V = V

+ 2 * L

L : Parasitic inductance.

V

: Clamping Voltage.

V : Residual overvoltage.

CL

di/dt

CL