Technical information

LCP1521S/LCP152DEE

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Technical information

Figure 5.

LCP152 concept behavior

Figure 5. shows the classical protection circuit using the LCP152 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

through Th1 becomes less negative than the holding current IH, then Th1 switches off.

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

surge current flows through the ground.

Figure 6.

Example of PCB layout based on LCP152S protection

Figure 6. 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 to minimize the dynamical breakover voltage at the SLIC Tip and Ring inputs

during fast strikes. Note that this capacitor is generally present around the SLIC - Vbat pin.

So to be efficient it has to be as close as possible from the LCP152 Gate pin and from the

reference ground track (or plan) (see Figure 6.). The optimized value for C is 220 nF.

The series resitors Rs1 and Rs2 designed in Figure 5. represent the fuse resistors or the

PTC which are mandatory to withstand the power contact or the power induction tests

GND

Gate

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

LCP1521S