TISP7xxxF3 (MV, HV) Overvoltage Protector Series
APPLICATIONS INFORMATION
Protection Voltage
The protection voltage, (V
), increases under lightning surge conditions due to thyristor regeneration. This increase is dependent on the
(BO)
rate of current rise, di/dt, when the TISP device is clamping the voltage in its breakdown region. The V
®
value under surge conditions can
(BO)
(250 V/ms) value by the normalized increase at the surge’s di/dt. An estimate of the di/dt can
be estimated by multiplying the 50 Hz rate V
be made from the surge generator voltage rate of rise, dv/dt, and the circuit resistance.
(BO)
As an example, the ITU-T recommendation K.21 1.5 kV, 10/700 surge has an average dv/dt of 150 V/µs, but, as the rise is exponential, the
initial dv/dt is three times higher, being 450 V/µs. The instantaneous generator output resistance is 25 Ω. If the equipment has an additional
series resistance of 20 Ω, the total series resistance becomes 45 Ω. The maximum di/dt then can be estimated as 450/45 = 10 A/µs. In
practice, the measured di/dt and protection voltage increase will be lower due to inductive effects and the finite slope resistance of the TISP
breakdown region.
®
Capacitance
Off-State Capacitance
®
The off-state capacitance of a TISP device is sensitive to junction temperature, T , and the bias voltage, comprising of the dc voltage, V ,
J
D
and the ac voltage, V . All the capacitance values in this data sheet are measured with an ac voltage of 1 Vrms. When V >> V , the capaci-
d
D
d
tance value is independent on the value of V . Up to 10 MHz, the capacitance is essentially independent of frequency. Above 10 MHz, the
d
effective capacitance is strongly dependent on connection inductance. For example, a printed wiring (PW) trace of 10 cm could create a circuit
resonance with the device capacitance in the region of 80 MHz.
Longitudinal Balance
®
Figure 35 shows a three terminal TISP device with its equivalent “delta” capacitance. Each capacitance, C , C
terminal pair capacitance measured with a three terminal or guarded capacitance bridge. If wire R is biased at a larger potential than wire T,
and C , is the true
TR
TG RG
then C
> C
. Capacitance C
is equivalent to a capacitance of C
in parallel with the capacitive difference of (C ). The line
-C
TG
RG
TG
capacitive unbalance is due to (CTG -C
RG
TG RG
) and the capacitance shunting the line is C
+C /2 .
TR RG
RG
Figure 35.
All capacitance measurements in this data sheet are three terminal guarded to allow the designer to accurately assess capacitive unbalance
effects. Simple two terminal capacitance meters (unguarded third terminal) give false readings as the shunt capacitance via the third terminal is
included.
MARCH 1994 - REVISED MARCH 2006
Specifications are subject to change without notice.
Customers should verify actual device performance in their specific applications.
BOURNS [ BOURNS ELECTRONIC SOLUTIONS ]
