AN2689 datasheet(21/42 Pages) STMICROELECTRONICS

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AN2689

Supply rail protection

Doc ID 14310 Rev 3

21/42

Supply rail protection

4.1

Protection topology

4.1.1

Clamping topology

For supply rail protection the recommended topology is the “clamping topology”.

Figure 25 shows a schematic of the supply rail protection topology.

Figure 25.

Supply rail protection using a Transil

The choice of the protection device depends on the surge that is applied. To illustrate the

possible device selection, two protection examples are given below.

4.2

Supply rail protection example 1: pulse 2 ISO 7637-2

Pulse 2 from ISO 7637-2 standard corresponds to a surge, which is produced by a sudden

interruption of current in a device connected in parallel with the Transil, due to inductance in

the wiring harness. The pulse is directly applied to the battery and is a positive pulse. See

Figure 26 for the pulse characteristics.

The typical parameters are:

●

Rise time (10-90%) - approximately 10 µs (tr)

●

Pulse width (10-90%) - typically 50 µs (td)

●

Pulse amplitudes from +37 V to +50 V (Vs)

●

Pulse repetition from 0.2 Hz to 5 Hz (F)

●

Output impedance 2



Module to protect

Vnom

Vmax

Transil

Vbat

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