SMT50 ELECTRICAL CHARACTERISTICS The electrical characteristics of a SMT50 device are similar to device is reached (Ibo) which causes the device to switch to a that of a self-gated Triac, but the SMT50 is a two terminal fully conductive state such that the voltage across the device device with no gate. The gate function is achieved by an is now only a few volts (Vt). The voltage at which the device internal current controlled mechanism. switched from the avalanche mode to the fully conductive state (Vt) is known as the Breakover voltage (Vbo). When the Like the T.V.S. diodes, the SMT50 has a standoff voltage (Vrm) device is in the Vt state, high currents can be diverted which should be equal to or greater than the operating without damage to the SMT50 due to the low voltage across voltage of the system to be protected. At this voltage (Vrm) the device, since the limiting factor in such devices is the current consumption of the SMT50 is negligible and will dissipated power (V x I). not affect the protected system. Resetting of the device to the non-conducting state is When a transient occurs, the voltage across the SMT50 will controlled by the current flowing through the device. When increase until the breakdown voltage (Vbr) is reached. At this the current falls below a certain value, known as the Holding point the device will operate in a similar way to a T.V.S. Current (Ih), the device resets automatically. device and is in avalanche mode. As with the avalanche T.V.S. device, if the SMT50 is subjected The voltage of the transient will now be limited and will only to a surge current which is beyond its maximum rating, then increase by a few volts as the device diverts more current. As the device will fail in short circuit mode, ensuring that the this transient current rises, a level of current through the equipment is ultimately protected. SELECTING A SMT50 1. When selecting a SMT50 device, it is important that I V-I Graph illustrating symbols the Vrm of the device is equal to or greater than the and terms for the SMT50 surge the operating voltage of the system. protection device. Ipp IBO IH 2. The minimum Holding Current (Ih) must be greater IRM otherwise the device will remain conducting following a transient condition. COMPLIES WITH THE FOLLOWING STANDARDS PEAK SURGE VOLTAGE (V) VOLTAGE WAVEFORM (µS) CURRENT WAVEFORM ADMISSIBLE IPP NECESSARY RESISTOR (µS) (A) (Ω) (CCITT) ITU-K20 1000 10/700 5/310 25 - (CCITT) ITU-K17 1500 10/700 5/310 38 - VDE0433 2000 10/700 5/310 50 - VDE0878 2000 1.2/50 1/20 50 - IEC-1000-4-5 level 3 10/700 5/310 50 - level 4 1.2/500 8/20 100 - 1500 10/160 10/160 75 12.5 type A 800 10/560 10/560 55 6.5 FCC Part 68, lightning surge 1000 9/720 5/320 25 11.5 FCC Part 68, lightning surge type B Bellcore TR-NWT-001089 2500 2/10 2/10 150 first level 1000 10/1000 10/1000 50 10 Bellcore TR-NWT-001089 5000 2/10 2/10 150 11.5 1000 0.5/700 0.8/310 25 - second level CNET I31-24 48 V VRM than the current the system is capable of delivering w w w. l i t t e l f u s e . c o m VBR VBO VR SMT50 ELECTRICAL CHARACTERISTICS (Tamb 25°C) SYMBOL PARAMETER SYMBOL PARAMETER V RM Stand-off Voltage V BO Breakover Voltage I RM Leakage Current at Stand-off Voltage IH Holding Current VR Continuous Reverse Voltage I BO Breakover Current V BR Breakdown Voltage I PP Peak pulse Current C Capacitance THERMAL RESISTANCE SYMBOL PARAMETER VALUE UNIT RTH (J-I) Junction to leads 20 RTH (J-I) Junction to ambient on printed circuit (with standard footprint dimensions) 100 °C/W °C/W ABSOLUTE MAXIMUM RATINGS (Tamb 25°C) SYMBOL PARAMETER P Power dissipation IPP Peak pulse current VALUE UNIT Tlead 5 W 10/1000µS 50 A 8/20µS 100 A tp + 20ms 30 A VRM 5 KV/µS -55 to +150 I TSM Non repetitive surge peak on-state current dV/dt Critical rate of rise of off-state voltage Tstg Storage temperature range Tj Maximum junction temperature 150 °C °C TL Maximum lead temperature for soldering during 10s 260 Tstg Type Marking IRM @ VRM MAX IRM @ VR MAX VBO @ IBO MAX IH MIN C MAX (Note 1) Laser (µA) (V) (µA) (V) (V) (mA) (mA) (pF) SMT50-62 A062 2 56 50 62 82 800 150 150 SMT50-68 A068 2 60 50 68 90 800 150 150 SMT50-100 A100 2 90 50 100 133 800 150 100 SMT50-120 A120 2 180 50 120 160 800 150 100 SMT50-130 A130 2 117 50 130 173 800 150 100 SMT50-180 A180 2 162 50 180 240 800 150 100 SMT50-200 A200 2 180 50 200 267 800 150 100 SMT50-220 A220 2 198 50 220 293 800 150 100 SMT50-240 A240 2 216 50 240 320 800 150 100 SMT50-270 A270 2 243 50 270 360 800 150 100 All parameters are tested @ 25°C except where indicated. Note 1: Measured @ 1V bias, 1MHZ TM All parameters are tested using a FET TEST model 3600 w w w. l i t t e l f u s e . c o m 49 SMT50 50 w w w. l i t t e l f u s e . c o m