JUNE 1999 - REVISED JANUARY 2007

Specifications are subject to change without notice.

Customers should verify actual device performance in their specific applications.

Impulse Testing (continued)

AC Testing

Capacitance

APPLICATIONS INFORMATION

If the impulse generator current exceeds the protector’s current rating, then a series resistance can be used to reduce the current to the

protector’s rated value to prevent possible failure. The required value of series resistance for a given waveform is given by the following

calculations. First, the minimum total circuit impedance is found by dividing the impulse generator’s peak voltage by the protector’s rated

current. The impulse generator’s fictive impedance (generator’s peak voltage divided by peak short circuit current) is then subtracted from the

minimum total circuit impedance to give the required value of series resistance. In some cases, the equipment will require verification over a

temperature range. By using the rated waveform values from Figure 10, the appropriate series resistor value can be calculated for ambient

temperatures in the range of -40 °C to 85 °C.

The protector can withstand currents applied for times not exceeding those shown in Figure 7. 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 from opening during impulse testing. The current

versus time characteristic of the overcurrent protector must be below the line shown in Figure 7. In some cases, there may be a further time

limit imposed by the test standard (e.g. UL 1459/1950 wiring simulator failure).

Safety tests require that the equipment fails without any hazard to the user. For the equipment protector, this condition usually means that the

fault mode is short circuit, ensuring that the following circuitry is not exposed to high voltages. The ratings table and Figure 8 detail the earliest

times when a shorted condition could occur. Figure 8 shows how the protector current levels compare to UL 1950 levels. Only the UL 1950

600 V tests (1, 2 and 3) are shown, as these have sufficient voltage to operate the protector. Tests 4 (<285 V peak, 2.2 A) and 5 (120 V rms, 25

A) are too low in voltage to operate the protector.

Figure 8 shows that the TISP4360H3BJ curve is very close or better than the UL 1950 test levels. Design compliance is simply a matter of

(Surge Withstand type) series have a 600 V capability for UL 1950. Fuses rated in the range of 0.5 A to 1.5 A will usually meet the safety test

requirements. However, the lower rated current value fuses may open on the type A surges of FCC Part 68. Opening on a type A surge is not a

test failure, but opening on a type B surge (37.5 A 5/320) is; so the selected fuse must be able to withstand the type B surge.

The protector characteristic off-state capacitance values are given for d.c. bias voltage, VD, values of 0, -1 V, -2 V, -50 V and -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.

Normal System Voltage Levels

The protector should not clip or limit the voltages that occur in normal system operation. If the maximum system voltages are not known, then

designers often used the voltages for the FCC Part 68 “B” ringer. The “B” ringer has a d.c. voltage of 56.5 and a maximum a.c. ring voltage of

150 V rms. The resultant waveform is shown in Figure 13. The maximum voltage is -269 V, but, because of possible wiring reversals, the

protector should have a working voltage of ±269 V minimum. The standard TISP4350H3BJ protector meets this requirement with a working

voltage, VDRM, of ±275 V and a protection voltage, V(BO), of ±350 V. Figure 14 shows the TISP4350H3BJ voltages relative to the POTS -269 V

peak ringing voltage.

The ADSL signal can be as high as ±15 V and this adds to the POTS signal, making a peak value of -284 V. This increased signal value of

-284 V would be clipped by the TISP4350H3BJ, which only allows for a -275 V signal. The TISP4360H3BJ has been specified to overcome this

problem by having a higher working voltage of ±290 V. Figure 15 shows the TISP4360H3BJ voltages relative to the -284 V peak ADSL plus

POTS ringing voltage. The ±15 V ADSL signal is shown as a grey band in Figure 15.

The recommended PCB pad layout for the TISP4360H3BJ SMB package (see mechanical section) gives a creepage distance of 2.54 mm

between the device terminals. This distance value allows compliance to the minimum clearance values required by UL 1950 for operational,

basic and supplementary insulation and creepage values for pollution degree 1.

TISP4360H3BJ Overvoltage Protector Series