TISP61511D Gated Protectors
Impulse Conditions (Continued)
When the TISP switches into the on-state it has a very low impedance. As a result, although the surge wave shape may be defined in terms of
open circuit voltage, it is the current waveshape that must be used to assess the TISP surge requirement. As an example, the CCITT IX K17
1.5 kV, 10/700
µs
surge is changed to a 38 A 5/310
µs
waveshape when driving into a short circuit. The impulse generators used for rated
values are tabulated below
Impulse Generators used for Rated Values
Peak Voltage
Standard
TR-NWT-001089
ETS 300 047-1
RLM88/I3124
K17, K20, K21
TR-NWT-001089
Setting
V
2500
3000
1600
1600
1000
Voltage
Wave Form
µs
2/10
1.2/50
0.5/700
10/700
10/1000
Generator Fictive
Source Impedance
External
Series Resistance
Peak Current
A
170
80
40
40
30
Current
Wave Form
µs
2/10
0.6/18
0.2/310
5/310
10/1000
Y
5
38
40
40
10
Y
10
0
0
0
23
Figures 4. and 5. show how the TISP61511D limits negative and positive overvoltages. Negative overvoltages (Figure 4.) are initially clipped
close to the SLIC negative supply rail value (V
BAT
). If sufficient current is available from the overvoltage, then the protector (Th5) will crowbar
into a low voltage on-state condition. As the overvoltage subsides the high holding current of the crowbar prevents dc latchup. The protection
voltage will be the sum of the gate supply (V
BAT
) and the peak gate-cathode voltage (V
GK(BO)
). The protection voltage will be increased if there
is a long connection between the gate decoupling capacitor, C, and the gate terminal. During the initial rise of a fast impulse, the gate current
(I
G
) is the same as the cathode current (I
K
). Rates of 70 A/µs can cause inductive voltages of 0.7 V in 2.5 cm of printed wiring track. To
minimize this inductive voltage increase of protection voltage, the length of the capacitor to gate terminal tracking should be minimized.
Inductive voltages in the protector cathode wiring can increase the protection voltage. These voltages can be minimized by routing the SLIC
connection through the protector as shown in Figure 3.
SLIC
PROTECTOR
SLIC
SLIC
PROTECTOR
SLIC
I
K
Th5
TISP
61511D
C
220 nF
I
G
V
BAT
AI6XAB
I
F
Th5
TISP
61511D
V
BAT
220 nF
AI6XAC
Figure 4. Negative Overvoltage Condition
Figure 5. Positive Overvoltage Condition
Positive overvoltages (Figure 5.) are clipped to ground by forward conduction of the diode section in protector (Th5). Fast rising impulses will
cause short term overshoots in forward voltage (V
FRM
).
The thyristor protection voltage, (V
(BO)
) increases under lightning surge conditions due to thyristor regeneration time. This increase is depen-
dent on the rate of current rise, di/dt, when the TISP is clamping the voltage in its breakdown region. The diode protection voltage, known as
the forward recovery voltage, (V
FRM
) is dependent on the rate of current rise, di/dt. An estimate of the circuit di/dt can be made from the surge
generator voltage rate of rise, dv/dt, and the circuit resistance. The impulse generators used for characterizing the protection voltages are
tabulated on the next page.
JULY 1995 — REVISED MARCH 2006
Specifications are subject to change without notice.
Customers should verify actual device performance in their specific applications.
BOURNS [ BOURNS ELECTRONIC SOLUTIONS ]
