TISP7xxxF3 (MV, HV) Overvoltage Protector Series

APPLICATIONS INFORMATION

Protection Voltage

The

rate

protection

of current

voltage, (V(BO)

rise, di/dt, when

), increases under

the TISP® device

lightning surge

is clamping the

conditions

voltage in

due to thyristor regeneration. This increase is

its breakdown region. The V(BO) value under

dependent on the

surge conditions can

be estimated by multiplying the 50 Hz rate V(BO) (250 V/ms) value by the normalized increase at the surge’s di/dt. An estimate of the di/dt can

be made from the surge generator voltage rate of rise, dv/dt, and the circuit resistance.

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, TJ, and the bias voltage, comprising of the dc voltage, VD,

and the ac voltage, Vd. All the capacitance values in this data sheet are measured with an ac voltage of 1 Vrms. When VD >> Vd, the capaci-

tance value is independent on the value of Vd. Up to 10 MHz, the capacitance is essentially independent of frequency. Above 10 MHz, the

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, CTG, CRG and CTR, is the true

terminal pair capacitance measured with a three terminal or guarded capacitance bridge. If wire R is biased at a larger potential than wire T,

then CTG > CRG. Capacitance CTG is equivalent to a capacitance of CRG in parallel with the capacitive difference of (CTG -CRG). The line

capacitive unbalance is due to (CTG -CRG) and the capacitance shunting the line is CTR +CRG/2 .

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.