Specifications are subject to change without notice.

106

JANUARY 1999 - REVISED OCTOBER 2000

Normal System Voltage Levels (continued)

TISP3xxxH3SL Overvoltage Protector Series

APPLICATIONS INFORMATION

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 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 (1.89 ”). 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.