9
NOVEMBER 1997 - REVISED MA RCH 1999
TISP4070M3BJ THRU TISP4095M3BJ, TISP4125M3BJ THRU TISP4200M3BJ,
TISP4240M3BJ THRU TISP4400M3BJ
BIDIRECTIONAL THYRISTOR OVERVOLTAGE PROTECTORS
PRODUCT INFORMATION
Figure 15 and Figure 16. FCC Part 68 allows the equipment to be non-operational after the 10/160 (conductor
to ground) and 10/ 560 (inter-condu ctor) impuls es. The ser ies resistor value may be reduced to zero to pa ss
FCC Part 6 8 in a non- operation al mode e.g. Fi gure 14. In s ome cas es th e equi pment w ill req uire verifi catio n
over a temperature range. By using the rated waveform values from Figure 11, the appropriate series resistor
value can be calculated for ambient temperatures in the range of -40 °C to 85 °C.
a.c. power testing
The protec tor can withs tand curre nts applied for times n ot ex ceeding thos e shown in Figure 8 . Currents tha t
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
The protector characteristic off-state capacitance values are given for d.c. bias voltage, VD, values of 0, -1 V,
-2 V and -50 V. Whe re pos sible values are al so gi ven for -100 V. Values for othe r voltages m ay be calcul ated
by multiplying the VD= 0 capacit ance value by the fac tor given in Figure 6. Up t o 10 MHz the ca pacitanc e is
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 wi ll be ab out - 2 V a nd -50 V. Figure 7 sh ows the di fferential (line unba la nce) capa ci tanc e c aus ed 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.
Figure 10 allows the calculation of the protector VDRM value at temperatures below 25 °C. The calculated
value should not be less than the maximum normal system voltages. The TISP4265M3BJ, with a VDRM of
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. Howe v er, 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
level of clipping would occur at the temp erature when the VDRM has reduce d to 190/200 = 0.95 of its 25 °C
value. Figure 10 shows that this condition will occur at an ambient temperature of -28 °C. In this example, the
TISP4265M3BJ will allow normal equipment operation provided that the minimum expected ambient
temperature does not fall below -28 °C.
JESD51 thermal measurement method
To standardise thermal measurements, the EIA (Electronic Industries Alliance) has created the JESD51
standard. P art 2 of the standard (JESD51-2, 1995) describes the test environment. This is a 0.0283 m3 (1 ft3)
cube which contains the test PCB (Printed Circuit Board) horizontally mounted at the centre. Part 3 of the
standar d (JESD51- 3, 1996) defines two test PCBs for surface mount compon ents; one for packages small er
than 27 m m on a side and the othe r for packages up to 48 mm. The SMBJ me asureme nts used th e small er
76.2 mm x 114.3 mm (3.0 “ x 4.5 “) PCB. The JESD51-3 PCBs are designed to have low effective thermal
conducti vity (hi gh ther mal res istance) and represen t a worse case c ondition . The PCBs used in the ma jor ity
of applic ations will a chieve lower values of ther ma l resistan ce and so c an dissipat e higher power levels than
indicated by the JESD51 values.