AN589

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THEORICAL ANALYSIS

Figure 2. Equivalent diagram

Figure 2 A/ shows the internal circuit diagram of the 8 way protection device ITA25. We see that the cath-

odes of all channels are common. If we consider the two adjacent lines V1 and V2, we note that when V1

is more positive than V2, both channels are connected through the off state capacitance of one of the di-

odes (see Figure 2 B/).

We have the same phenomenon when V2 is more positive than V1 (see Figure 2 C/).

So the equivalent circuit of both driver and receiver lines is given by Figure 3. This diagram shows the

worse case, because the input resistance of the receiver 2 has not been taken into account and zero line

capacitance has been assumed.

The simulation results using this equivalent circuit are given in Figure 4.

The capacitance C is equal to 200 pF for a bias voltage of 12 V.

V1

V2

Vn

A/

V1

V2

B/

V1

V2

C/