AN2689 datasheet(8/42 Pages) STMICROELECTRONICS

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Parameters to consider in selecting protection devices

AN2689

8/42

Doc ID 14310 Rev 3

Parameters to consider in selecting protection

devices

To make the best choice in protection device and considering Figure 5, it is necessary to

consider several parameters such as:

●

Nominal voltage the electronic module runs with (Vnom)

●

Maximum voltage this electronic module can support (Vmax)

●

Kind of surge that the electronic module may be called upon to support

–

If the surge shape is exponential:

What is the surge maximum voltage (Vs)?

What is the surge duration and at what level is it measured (tp)?

What is the surge generator impedance (Rs)?

What is the number of cycles in the surge (1/f)?

–

If the surge is a DC surge:

What is the DC voltage level (Vdc)?

What is the duration of the surge (tp)?

What is the surge generator impedance (Rs)?

●

What is the ambient temperature (Tamb)?

●

What kind of protection package is preferred?

●

Is the electronic module a simple DC module or a digital one?

–

If digital:

What is the signal frequency (F)?

What are the rise and fall time of the surge signal (tr, tf)?

What is the maximum line capacitance (Cl)?

Figure 5.

Surge application topology

Module to protect

Vnom

Vmax

Protection

device (*)

Vcl

(*) Transil or rail-to-rail protection device

Surge

Generator

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