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LCP1521S-LCP1521SRL
PROGRAMMABLE TRANSIENT VOLTAGE SUPPRESSOR FOR SLIC PROTECTION
1/11
LCP1521S/LCP152DEEPROGRAMMABLE TRANSIENT VOLTAGE
SUPPRESSOR FOR SLIC PROTECTION
REV. 3
February 2005
FEATURES Dual programmable transient suppressor Wide negative firing voltage range:
VMGL = -150 V max. Low dynamic switching voltages:
VFP and VDGL Low gate triggering current: IGT = 5 mA max Peak pulse current: IPP = 30 A (10/1000 µs) Holding current: IH = 150 mA min Low space consuming package
DESCRIPTIONThese devices have been especially designed to
protect new high voltage, as well as classical
SLICs, against transient overvoltages.
Positive overvoltages are clamped by 2 diodes.
Negative surges are suppressed by 2 thyristors, their
breakdown voltage being referenced to -VBAT
through the gate.
These components present a very low gate
triggering current (IGT) in order to reduce the
current consumption on printed circuit board
during the firing phase.
BENEFITSTRISILs™ are not subject to ageing and provide a
fail safe mode in short circuit for a better protec-
tion. Trisils are used to help equipment to meet
various standards such as UL60950, IEC950 /
CSA C22.2, UL1459 and FCC part68. Trisils have
UL94 V0 resin approved (Trisils are UL497B ap-
proved [file: E136224]).
Table 1: Order Codes
Figure 1: LCP1521S Functional Diagram
Figure 2: LCP152DEE Functional Diagram
TM: TRISIL is a trademark of STMicroelectronics.ASD
(Application Specific Devices)
LCP1521S/LCP152DEE
Table 2: Compliances with the following Standards
Table 3: Thermal Resistances
Table 4: Electrical Characteristics (Tamb = 25°C)
LCP1521S/LCP152DEE3/11
Table 5: Absolute Ratings (Tamb = 25°C, unless otherwise specified)
Table 6: Repetitive peak pulse current
Table 7: Parameters related to the diode LINE / GND (Tamb = 25°C)
Note 1: see test circuit for VFP; RS is the protection resistor located on the line card.
LCP1521S/LCP152DEE
Table 8: Parameters related to the protection Thyristors (Tamb = 25°C, unless otherwise specified)
Table 9: Parameters related to diode and protection Thyristors(Tamb = 25°C, unless otherwise specified)
Figure 3: Functional Holding Current (IH) test circuit: GO-NO GO test
Note 2: see functional holding current (IH) test circuit
Note 3: see test circuit for VDG The oscillations with a time duration lower than 50ns are not taken into account.
LCP1521S/LCP152DEE5/11
Figure 4: Test circuit for VFP and VDGL parameters
TECHNICAL INFORMATION
Figure 5: LCP152 concept behaviorFigure 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.
LCP1521S/LCP152DEE
Figure 6: Example of PCB layout based on LCP152 protectionFigure 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 220nF.
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 imposed by the various country
standards. Taking into account this fact the actual lightning surge current flowing through the LCP is equal to:
I surge = V surge / (Rg + Rs)
With V surge = peak surge voltage imposed by the standard.
Rg = series resistor of the surge generator
Rs = series resistor of the line card (e.g. PTC)
e.g. For a line card with 30Ω of series resistors which has to be qualified under GR1089 Core 1000V
10/1000µs surge, the actual current through the LCP152 is equal to:
I surge = 1000 / (10 + 30) = 25A
The LCP152 is particularly optimized for the new telecom applications such as the fiber in the loop, the
WLL, the remote central office. In this case, the operating voltages are smaller than in the classical sys-
tem. This makes the high voltage SLICs particularly suitable.
The schematics of figure 7 on next page gives the most frequent topology used for these applications.
