AN2689 datasheet(17/42 Pages) STMICROELECTRONICS

17 / 42 page

AN2689

Data line protection

Doc ID 14310 Rev 3

17/42

Considering the ISO 10605 surge with Vpp = +25 kV, Rs = 2000  and Vbrmax = 28.4 V, the

calculation produces:

Then Vcl = 31.4 V and Ipp = 12.5 A

Therefore the maximum residual voltage that will be applied to the module is lower than the

maximum voltage admissible (<45 V).

The question now is to determine if the Transil is able to withstand the power of the surge.

The peak pulse power (Ppp) dissipated in the Transil is:

To see if this power can be supported by the Transil, it is necessary to determine the

duration of the current that crosses the Transil during the surge compared to the peak pulse

power versus exponential pulse duration graph shown in Figure 20 (also in the datasheet).

Care must be taken at this step because the duration to be considered is the pulse duration

at Ip/2. So it is necessary to determine the current surge duration (t’ in Figure 19) that

corresponds to half of the peak current crossing the Transil.

Figure 20.

Peak pulse power versus exponential pulse duration

µs

RsVbr

Vcl

max

µs

Vbr

Ipp

max

Ppp

Ipp

Vcl

Ppp

392

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AN2689 Datasheet(PDF) 17 Page - STMicroelectronics