DocID13397 Rev 5

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LCP1531

Technical information

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Technical information

Figure 4. LCP1531 concept behavior

Figure 4. shows the classical protection circuit using the LCP1531 crowbar concept. This

topology has been developed to protect the new high voltage SLICs. It allows to program

the negative firing threshold while the positive clamping value is fixed at GND.

When a negative surge occurs on one wire (L1 for example) a current IG flows through the

base of the transistor T1 and then injects a current in the gate of the thyristor Th1. Th1 fires

and all the surge current flows through the ground. After the surge when the current flowing

When a positive surge occurs on one wire (L1 for example) the diode D1 conducts and the

surge current flows through the ground.

Figure 5. Example of PCB layout based on LCP1531 protection

Figure 5. shows the classical PCB layout used to optimize line protection.

The capacitor C is used to speed up the crowbar structure firing during the fast surge edges.

This allows minimization of the dynamic breakover voltage at the SLIC Tip and Ring inputs

So to be efficient it has to be as close as possible from the LCP1531 Gate pin and from the

reference ground track (or plan) (see Figure 5.). The optimized value for C is 100 nF.

GND

Gn

TIP

RING

GND

-Vbat

C

Rs1

Rs2

L 1

L 2

V Tip

Th1

D1

T1

IG

ID1

To

line side

GND

To

SLIC side

LCP1531