151DHV Просмотр технического описания (PDF) - STMicroelectronics
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151DHV Datasheet PDF : 9 Pages
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LCP1521
TECHNICAL INFORMATION
Fig. A1: LCP1521 concept behavior.
L1
GND
Rs1
TIP
V Tip
ID1
IG
T1
Th1
D1
-Vbat Gate
GND
C
Rs2
L2
RING
VRing
Figure A1 shows the classical protection circuit using the LCP1521 crowbar concept. This topology
has been developed to protect the new high voltage SLIC’s. 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 tran-
sistor 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.
Fig. A2: Example of PCB layout based on LCP1521 protection.
To
line side
GND
To
SLIC side
In order to minimize the remaining voltage across the SLIC inputs during the surge, the TIP and RING pins
of the LCP1521 are doubled (Pins 1 and 8 for TIP / Pins 4 and 5 for RING).
This fact allows the board designer to connect the tracks like in figure A2. With such a PCB design, the ex-
tra voltages caused by track stray inductance remain located on the line side of the LCP and do not affects
the SLIC side.
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 LCP1521 Gate pin and from the reference
ground track (or plan) (see Fig. A2). The optimized value for C is 220nF.
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