9

NOVEMBER 1997 - REVISED APRIL 1999

TISP4070H3LM THRU TISP4095H3LM, TISP4125H3LM THRU TISP4220H3LM,

TISP4240H3LM THRU TISP4400H3LM

BIDIRECTIONAL THYRISTOR OVERVOLTAGE PROTECTORS

PR O D UC T

I N FO R M A T IO N

a.c. power testing

The protector can withstand currents applied for times not exceeding those shown in Figure 8. Currents that

exceed these times must be terminated or reduced to avoid protector failure. Fuses, PTC (Positive

Temperature Coefficient) resistors and fusible resistors are overcurrent protection devices which can be used

to reduce the current flow. Protective fuses may range from a few hundred milliamperes to one ampere. In

some cases it may be necessary to add some extra series resistance to prevent the fuse opening during

impulse testing. The current versus time characteristic of the overcurrent protector must be below the line

shown in Figure 8. In some cases there may be a further time limit imposed by the test standard (e.g. UL

1459 wiring simulator failure).

capacitance

-2 V and -50 V. Where possible values are also given for -100 V. Values for other voltages may be calculated

essentially independent of frequency. Above 10 MHz the effective capacitance is strongly dependent on

connection inductance. In many applications, such as Figure 15 and Figure 17, the typical conductor bias

voltages will be about -2 V and -50 V. Figure 7 shows the differential (line unbalance) capacitance caused by

biasing one protector at -2 V and the other at -50 V.

normal system voltage levels

The protector should not clip or limit the voltages that occur in normal system operation. For unusual

conditions, such as ringing without the line connected, some degree of clipping is permissible. Under this

condition about 10 V of clipping is normally possible without activating the ring trip circuit.

200 V, can be used for the protection of ring generators producing 100 V rms of ring on a battery voltage of

-58 V (Th2 and Th3 in Figure 17). The peak ring voltage will be 58 + 1.414*100 = 199.4 V. However, this is the

open circuit voltage and the connection of the line and its equipment will reduce the peak voltage. In the

extreme case of an unconnected line, clipping the peak voltage to 190 V should not activate the ring trip. This

value. Figure 10 shows that this condition will occur at an ambient temperature of -22 °C. In this example, the

TISP4260H3LM will allow normal equipment operation provided that the minimum expected ambient

temperature does not fall below -22 °C.

JESD51 thermal measurement method

To standardise thermal measurements, the EIA (Electronic Industries Alliance) has created the JESD51

cube which contains the test PCB (Printed Circuit Board) horizontally mounted at the centre. Part 3 of the

standard (JESD51-3, 1996) defines two test PCBs for surface mount components; one for packages smaller

than 27 mm on a side and the other for packages up to 48 mm. The LM package measurements used the

smaller 76.2 mm x 114.3 mm (3.0 “ x 4.5 “) PCB. The JESD51-3 PCBs are designed to have low effective

thermal conductivity (high thermal resistance) and represent a worse case condition. The PCBs used in the

majority of applications will achieve lower values of thermal resistance and so can dissipate higher power

levels than indicated by the JESD51 values.