LCP concept

AN2053

4/15

Doc ID 10917 Rev 2

2

LCP concept

Figure 5.

LCP15xx concept behavior

Figure 5 shows the classical protection circuit using the LCP15xx crowbar concept. This

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

be programmed for the negative firing threshold while the positive clamping value is fixed at

GND.

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

on and all the surge current is short circuited to ground. After the surge, when the current

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

surge current is short circuited to ground.

In order to minimize the remaining voltage across the SLIC inputs during the surge, a 4 point

structure has been implemented (Pins 1 and 8 for TIP / Pins 4 and 5 for RING). This fact

allows the board designer to connect the track as designed in Figure 6. With such a PCB

located on the line side of the LCP and do not affect its SLIC side.

The capacitor C is used to speed up the crowbar structure firing during the fast negative

surge edges. This allows the dynamic breakover voltage at the SLIC Tip and Ring inputs to

be minimized during fast strikes. Please note that this capacitor is generally present around

Gate pin and to the reference ground track (or plan) (see Figure 6). Optimized value for C is

220 nF.

V Ring

GND

Gate

TIP

RING

GND

-Vbat

C

Rs1

Rs2

L 1

L 2

V Tip

Th1

D1

T1

Ig

ID1