TISP4xxxM3BJ Overvoltage Protector Series
AC Power Testing
The protector can withstand currents applied for times not exceeding those shown in Figure 9. Currents that exceed these times must be
terminated or reduced to avoid protector failure. Fuses, PTC (Positive Temperature Coefficient) thermistors 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 9. 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. Where possible
values are also given for -100 V. Values for other voltages may be calculated by multiplying the VD = 0 capacitance value by the factor given in
Figure 6. Up to 10 MHz, the capacitance is essentially independent of frequency. Above 10 MHz, the effective capacitance is strongly
dependent on connection inductance. In many applications, such as Figure 16 and Figure 18, 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.
Figure 8 shows the typical capacitance asymmetry; the difference between the capacitance measured with a positive value of VD and the
capacitance value when the polarity of VD is reversed. Capacitance asymmetry is an important parameter in ADSL systems where the
protector often has no d.c. bias and the signal level is in the region of
±10
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 11 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 18). 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 level of clipping would occur at the temperature
when the VDRM has reduced to 190/200 = 0.95 of its 25
°C
value. Figure 11 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 standardize thermal measurements, the EIA (Electronic Industries Alliance) has created the JESD51 standard. Part 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 center. 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 SMBJ 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 worst case condition. The PCBs used in the majority of applications will achieve lower values of thermal resistance, and can
dissipate higher power levels than indicated by the JESD51 values.
NOVEMBER 1997 - REVISED FEBRUARY 2005
Specifications are subject to change without notice.
Customers should verify actual device performance in their specific applications.
BOURNS [ BOURNS ELECTRONIC SOLUTIONS ]
