AN2689 datasheet(16/42 Pages) STMICROELECTRONICS

Part #	AN2689

Description	Protection of automotive electronics from electrical hazards

PDF	42 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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16 / 42 page

Data line protection

AN2689

16/42

Doc ID 14310 Rev 3

During an ESD strike, the voltage diagrams look like those given in Figure 19.

Figure 19.

Voltage diagrams during an ESD strike

3.3.2

Power dissipation determination

To make sure the power of the surge will not damage the Transil we need to determine the

power dissipated in the Transil.

Dissipated power is given by:

and

In this study, the transient duration is much lower than 20 µs, therefore we consider Rd

equivalent to Rd20 µs.

This Rd20µs can be easily calculated thanks to the Transil datasheets (see example given in

Section 3.3.1: Determination of Rd for SM6T27AY)

Then the power dissipation can be determined from:

Ip/2

Vcl

t’

τ = RC

ESD waveform

Voltage and current

across the transil

Ipp

Vbr

Vcl

Ipp

Vcl

Ppp

µs

Ipp

Vbr

Vcl

max

20 µs

=0.24

µs Ipp

Vbr

Vcl

max +

µs

Vbr

Ipp

max

Vbrmax

≈ Vbrmin + 10%

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