Introduction This section covers the overvoltage protection func-tions and Bourns TISP > ή (Totally Integrated SurgeProtector) thyristor SPDs (Surge Protective Devices) in terms of evolution, function, silicon structure, electrical characteristics, electrical rating and device variants. Basic Protection Function SPDs have a non-linear voltage-current characteristic which limits overvoltages by diverting the current caused by an overvoltage. Figure 1 shows how a two- terminal SPD is applied to limit the voltage between two conductors and one conductor and ground. There are two basic types of SPD characteristics; clamping and switching. > SPDSPD VoltageLimiting VoltageLimiting Figure 1. SPD Circuit Application OCTOBER 2000 - REVISED AUGUST 2001 size="-4">

Junction Termination The technology used for junction termination at thechip surface was decided by future needs and perfor- mance history. Three common ways of controlling junction breakdown at the surface are shown in Figure 5. Glassed Mesa technology terminates the high voltage junction on the edge of a mesa created by grooving the silicon wafer. The mesa is sealed with a layer of glass to prevent contamination and reduce thesurface field strength. Planar brings a lateraljunction up to the top surface. Thesurface is sealed with silicondioxide in thejunction area. Additional stability is provided...

The use of a breakdown pad considerably reducesthe breakdown voltage sensitivity to surface states. Chip surface voltage control will still be required, but the chances of premature surface breakdown are now considerably reduced. Figure 7 shows a typical TISP base junction of transistor TR2. The current path isthrough transistor TR2, and resistor RH.The current levels are very low during this condition as shown in Figure 6.The breakdown region initiateswhen the applied voltage is sufficient to cause the diode D1,to avalanche. As the diode D1 isintegrated with transistor TR2, thebreakdown region...

Switching Quadrant Blocking Quadrant > TR2TR1 On State Breakdown RHD1TR2TR1 Switch OffSwitch On > RHD1TR2 RHTR2TR1 RHD1TR2 -v-i +i + v Off StateBlocking > RHTR2 Figure 9. Protector Equivalent Circuits and VI characteristic > Figure 10. Reverse Blocking Unidirectional Thyristor > OCTOBER 2000 - REVISED AUGUST 2001 7 size="-1">

I > TSP SwitchingCharacteristic +v +iV I > TSM On-stateRegion I > T (BO) V > T SwitchingRegion I I > (BO) H BreakdownRegion I > DRM I > D V > D V > DRM -i Off-stateRegion > OCTOBER 2000 - REVISED AUGUST 2001

non-adjacent electrode connection to the gate. Inaddition to complimentary SCRs, this bidirectional function is given by a device called a TRIAC (Triode for Ac Control), which is used in 50 Hz/60 Hz applications.In the current-triggered mode, the SCRs providecurrent limiting to the protected load. By incorporat- ing a defined voltage breakdown region in the SCR structures, the SCRs will limit the maximum voltage to the load as well, by operating as fixed voltage protectors. When operating in the fixed voltage mode, the current from the protected load is not needed to cause switching. > +iv GA...

+ -v > G +i > G v - > GK Figure 18. Simplified Voltage Tracking Protection Circuit > OCTOBER 2000 - REVISED AUGUST 2001 size="-3">

V > G V D4Th1 > K Voltage - V SLIC -60-50-40-30-20-10010 I I > G Time - ms05101520 > K R > AC V K I > K I > G = +80 mA > Bat V AC D2 I C2D3V > G = zero > Switching ModePower SupplyD1Tx V G ACInductionTest I > K IG - Gate Current - mA IK - Cathode Current - mA -80-60-40-2002040 6080100 C1 -300-200 -1000100200300 -100 Time - ms05101520 > IG(AV) - Average Gate Current - mA G(AV) G OCTOBER 2000 - REVISED AUGUST 2001 size="-1">

Transistor Buffered = +1.6 mA > G Transistor Buffered = -7 mAI I > G I > IG - Gate Current - mA IK - Cathode Current - mA K -300-200-1000100200300 -100-80-60-40-20020406080100 Time - ms05101520 > OCTOBER 2000 - REVISED AUGUST 2001 size="-1">