AN2689 datasheet(28/42 Pages) STMICROELECTRONICS

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Supply rail protection

AN2689

28/42

Doc ID 14310 Rev 3

4.4

Supply rail protection example 2: pulse 5a load dump

ISO 7637-2

The load dump is caused by the discharged battery being disconnected from the alternator

while the alternator is generating charging current

Parameters are:

●

Pulse width -td [40 to 400 ms]

●

Pulse amplitude -Vs [65 to 87 V]

●

Impedance is Rs [0.5  to 4 

●

Vbat = 13.5 V

Figure 37.

ISO 7637-2, pulse 5a waveform characteristics

Figure 38.

Load dump protection test set up

In the same manner as for the last case (ISO pulse 2), we have to determine if the residual

voltage after the protection device is safe for the electronic module and if the power

dissipation involved in the protection device during the suppression is supported by the

protection device itself.

Consider now the RBO40-40 device (see Figure 39) which offers a surge protection

capability and a reverse battery protection.

bat

0.1Vs

0.9Vs

Module to protect

Vnom =13.5 V

Vmax =45 V

Tmax = 85 °C

Vcl

Surge

Generator

Vs = 87 V

Rs =2

td = 100 ms

Tr = 10 ms

Vbat = 13.5 V

Transil

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