AN2689 datasheet(13/42 Pages) STMICROELECTRONICS

13 / 42 page

AN2689

Data line protection

Doc ID 14310 Rev 3

13/42

If we consider the +25 kV air discharge surge test, then, regarding the suggested

application given in Figure 16: the worked example below may be used as a guideline for

protection solution selection.

Figure 16.

ISO 10605 ESD test set-up

Identification of the best protection (Transil)

About the module to protect:

●

The protection shall be “transparent” for the normal operating conditions of the module,

in this case 13.5 V.

●

The maximum voltage the module can withstand is 45 V so the Transil will not offer a

higher voltage than 45 V when acting.

●

The max temperature is 85 °C.

About the surge to suppress:

●

The maximum voltage (Vpp) of the surge is 25 kV.

●

The surge time constant duration

 is 660 ns (R*C).

●

The maximum repetition is one strike (t1).

●

The internal series resistor of the generator is 2 k

.

About the Transil:

●

The suppressor has the following electrical characteristics (Figure 17):

Figure 17.

Transil diode electrical characteristics

Where:

Vrm is the stand-off voltage measured @Irm. This corresponds to the nominal voltage of the

application Vrm13.5 V.

Module to protect

Vnom

= 13.5 V

Vmax

= 45 V

Tmax

= 85 °C

Vcl

Surge

Generator

Vs = 25 kV contact

= 2 k

≤ 1 ns

Vrm

Vbr

Vcl

Irm

Ipp

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