AN2689 datasheet(37/42 Pages) STMICROELECTRONICS

Part #	AN2689

Description	Protection of automotive electronics from electrical hazards

PDF	42 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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37 / 42 page

AN2689

PCB layout recommendations

Doc ID 14310 Rev 3

37/42

5.1.2

Capacitive and inductive coupling

The parasitic capacitance (see Figure 47) is due to the geometrical conception of the PCB

and the routing together. Figure 55 shows the effective capacitive coupling during surge

suppression.

Figure 55.

Capacitive coupling representation

This parasitic capacitance depends on the PCB and track structures as shown in Figure 56

and Figure 57. This parasitic capacitance is defined by the space between tracks, the track

width and the PCB thickness as well.

Figure 56.

Double side PCB structure in coplanar

Figure 57.

Track to track capacitance for double side PCB (source AEMC)

The longer is the line to the protection device, the higher will be the capacitive coupling.

Vsurge

εr=4.5

Capacitance (pF/cm)

0.1

0.01

0.001

0.3

0.03

0.003

0.1

0.3

h / w = 0.3

h / w = 0.5

h / w = 1

h / w = 2

h / w = 5

h / w = 10

d/h

AN2689 Datasheet(PDF) 37 Page - STMicroelectronics