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AN576

In the case of Figure 4, the design topology is based on a 4 point circuit. When a surge occurs the Transil

clamps at Vcl and due to the design the di/dt effects remain on the left hand side of P. Therefore the volt-

Figure 4. Optimized layout for ESD

N.B.: The surface mount family SOD6 and SOD15 are particularly suited to this kind of application.

Figure 5. Printer circuit board protection against ESD with case

These days most inputs are protected against ESD (though not always effectively) and so the voltage be-

tween the lines and ground never exceeds dangerous values.

However, this does not prevent the total electrical potential from increasing, possibly resulting in sparks

between one point of the board and the module case. To avoid this problem we recommend a bidirectional

Transil (BZW04P37B) between the printed circuit board ground and the metallic parts of the case.

U

DEVICE

TO BE

PROTECTED

P

I

V

CL

DISTURBANCE

SOURCE

PRINTED BOARD

MODULE CASE