OCTOBER 2000 - REVISED FEBRUARY 2005
Specifications are subject to change without notice.
Customers should verify actual device performance in their specific applications.
TISP61089B High Voltage Ringing SLIC Protector
Gated Protectors (Continued)
SLICs have become more sophisticated. To minimize power consumption, some designs automatically adjust the driver supply voltage to a
value that is just sufficient to drive the required line current. For short lines, the supply voltage would be set low, but for long lines, a higher
supply voltage would be generated to drive sufficient line current. The optimum protection for this type of SLIC would be given by a protection
voltage which tracks the SLIC supply voltage. This can be achieved by connecting the protection thyristor gate to the SLIC VBATH supply,
Figure 6. This gated (programmable) protection arrangement minimizes the voltage stress on the SLIC, no matter what value of supply voltage.
Figure 6. TISP61089B Buffered Gate Protector (‘1089 Section 4.5.12 Testing)
R1
40
Ω
Ω
Ω
Ω
RING
WIRE
TIP
WIRE
SLIC
TISP61089B
V
BATH
C1
220 nF
AI6XCC
600 Ω
Ω
Ω
Ω
600 Ω
Ω
Ω
Ω
A.C.
GENERATOR
0 - 600 V r.m.s.
SWITCHING MODE
POWER SUPPLY
GENERATOR
SOURCE
RESISTANCE
I
G
I
SLIC
C2
D1
Tx
R2
40
Ω
Ω
Ω
Ω
V
BATL
I
BATH
Figure 7. Negative Overvoltage Condition
I
G
Th5
SLIC
SLIC
PROTECTOR
I
K
AI6XAHB
V
BATH
TISP
61089B
C1
220 nF
Figure 8. Positive Overvoltage Condition
Th5
SLIC
V
BATH
SLIC
PROTECTOR
TISP
61089B
C1
220 nF
I
F
AI6XAIB
Operation of Gated Protectors
Figure 7 and Figure 8 show how the TISP61089B limits negative and positive overvoltages. Positive overvoltages (Figure 8) are clipped by the
antiparallel diode of Th5 and the resulting current is diverted to ground. Negative overvoltages (Figure 7) are initially clipped close to the SLIC
negative supply rail value (VBATH). If sufficient current is available from the overvoltage, then Th5 will switch into a low voltage on-state
condition. As the overvoltage subsides the high holding current of Th5 prevents d.c. latchup. The protection voltage will be the sum of the gate
supply (VBATH) and the peak gate-cathode voltage (VGK(BO)). The protection voltage will be increased if there is a long connection between the
gate decoupling capacitor, C1, and the gate terminal. During the initial rise of a fast impulse, the gate current (IG) is the same as the cathode
current (IK). Rates of 80 A/µs can cause inductive voltages of 0.8 V in 2.5 cm of printed wiring track. To minimize this inductive voltage increase of
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