AN588 datasheet(5/12 Pages) STMICROELECTRONICS

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AN588 APPLICATION NOTE

Choice of the break-down voltage (VBR) of the ITAxxB: In the case of symmetrical signals (±VLINE), a

bi-directional Transil array with a break-down voltage (VBR) greater than the maximum differential voltage

between the 2 wires must be used.

Figure 5 helps to understand the break-down voltage (VBR) calculation:

VBR > 2 * VL.

Each line is protected in the common mode at a voltage equal to the VBR, and the line signals are not

clamped in the differential mode.

Figure 5. Calculation of the Breakdown Voltage (VBR)

Examples of the use of bi-directional transil arrays

An ITAxx assures protection, even after its destruction

When a disturbance occurs whose energy is greater than the dissipation capability of the component, the

destruction mode is a short-circuit.

This behavior, linked to the physical laws of silicon but also to an adequate wiring, assures constant pro-

tection, even after destruction. Additionally the line failure detection is immediate.

Use of transil arrays as an EMI filter

By using these transil arrays, the EMI filter function is offered "for free". The combination of the junction

capacitance (from 500 to 1000pF) with the parasitic inductances of the PC board tracks (L = 10nH/cm)

creates an EMI filter whose attenuation can satisfy applications with low exposure levels such as centron-

ics connection in printers (see Figure 6).

Maximum Line Signals

ITAxxB Solutions

± 5 V

ITA10Bx

± 9 V

ITA18Bx

±12 V

ITA25Bx

+/-V L

Line 1

Line 2

VBR > 2 * VL

Vd = VBR + VF > ( +/- VL ) + ( +/- VL )

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