TISP3070H3SL THRU TISP3095H3SL, TISP3125H3SL THRU TISP3210H3SL
TISP3250H3SL THRU TISP3350H3SL
DUAL BIDIRECTIONAL THYRISTOR OVERVOLTAGE PROTECTORS
JANUARY 1999 - REVISED MAY 1999
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 TISP3290H3, with a VDRM of 220 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
220 V 25 °C VDRM value by a factor of 206.5/220 = 0.94. Figure 9 shows that a 0.94 reduction will occur at an
ambient temperature of -32 °C. In this example, the TISP3290H3 will allow normal equipment operation, even
on an open-circuit line, provided that the minimum expected ambient temperature does not fall below -32 °C.
JESD51 thermal measurement method
To standardise 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 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 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 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.
P R O D U C T
I N F O R M A T I O N
10
POINN [ POWER INNOVATIONS LTD ]
