TISP7xxxH3SL Overvoltage Protector Series
APPLICATIONS INFORMATION
AC Power Testing
The protector can withstand the G return 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
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. For example, a printed wiring (PW) trace of 10 cm could create a circuit resonance with the device
capacitance in the region of 50 MHz. In many applications, 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.
Figure 9 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 TISP7290H3, with a VDRM of 230 V, can be used for the protection of ring generators producing
105 V rms of ring on a battery voltage of -58 V. The peak ring voltage will be 58 + 1.414*105 = 206.5 V. However, this is the open circuit voltage
and the connection of the line and its equipment will reduce the peak voltage.
For the extreme case of an unconnected line, the temperature at which clipping begins can be calculated using the data from Figure 9. To
possibly clip, the VDRM value has to be 206.5 V. This is a reduction of the 230 V 25
°C
VDRM value by a factor of 206.5/230 = 0.90. Figure 9
shows that a 0.90 reduction will occur below an ambient temperature of -40
°C.
For this example, the TISP7290H3 will allow normal equipment
operation, even on an open-circuit line, down to below -40
°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 (1.06 ’’) on a side and the other for packages up to 48 mm (189 ’’). The thermal 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 resis-
tance) 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.
MARCH 1999 - REVISED FEBRUARY 2005
Specifications are subject to change without notice.
Customers should verify actual device performance in their specific applications.
BOURNS [ BOURNS ELECTRONIC SOLUTIONS ]
