Tvs Diode Array Spa Diodes Page 8 TVS Diode Array SPA Diodes Catalog

2017 Littelfuse, Inc. Specifications are subject to change without notice. Revised: 02/23/17 TVS Diode Arrays (SPA Diodes) Transient Threats - What Are Transients? Voltage Transients are defined as short duration surges of electrical energy and are the result of the sudden release of energy previously stored or induced by other means, such as heavy inductive loads or lightning. In electrical or electronic circuits, this energy can be released in a predictable manner via controlled switching actions, or randomly induced into a circuit from external sources. Repeatable transients are frequently caused by the operation of motors, generators, or the switching of reactive circuit components. Random transients, on the other hand, are often caused by Lightning and Electrostatic Discharge (ESD). Lightning and ESD generally occur unpredictably, and may require elaborate monitoring to be accurately measured, especially if induced at the circuit board level. Numerous electronics standards groups have analyzed transient voltage occurrences using accepted monitoring or testing methods. The key characteristics of several transients are shown in the table below. VOLTAGE CURRENT RISE-TIME DURATION Lighting 25kV 20kA 10 s 1ms Switching 600V 500A 50s 500ms EMP 1kV 10A 20ns 1ms ESD 8kV 30A <1ns 100ns Table 1. Examples of transient sources and magnitude Characteristics of Transient Voltage Spikes Transient voltage spikes generally exhibit a "double exponential" wave, as shown below for lightning and ESD. t1 t2 Vp Vp/2 t Figure 1. Lightning Transient Waveform 100% 90% I 10% 30n 60n tr = 0.7 to 1.0ns Current (I) % 30 60 Figure 2. ESD Test Waveform The exponential rise time of lightning is in the range 1.2sec to 10sec (essentially 10% to 90%) and the duration is in the range of 50sec to 1000sec (50% of peak values). ESD on the other hand, is a much shorter duration event. The rise time has been characterized at less than 1.0ns. The overall duration is approximately 100ns. Why are Transients of Increasing Concern? Component miniaturization has resulted in increased sensitivity to electrical stresses. Microprocessors for example, have structures and conductive paths which are unable to handle high currents from ESD transients. Such components operate at very low voltages, so voltage disturbances must be controlled to prevent device interruption and latent or catastrophic failures. Sensitive microprocessors are prevelant today in a wide range of devices. Everything from home appliances, such as dishwashers, to industrial controls and even toys use microprocessors to improve functionality and efficiency. Most vehicles now also employ multiple electronic systems to control the engine, climate, braking and, in some cases, steering, traction and safety systems. Many of the sub- or supporting components (such as electric motors or accessories) within appliances and automobiles present transient threats to the entire system. Careful circuit design should factor environmental scenarios as well as the potential effects of these related components. Table 2 below shows the typical vulnerability of various component technologies. Device Type Vulnerability (volts) VMOS 30-1800 MOSFET 100-200 GaAsFET 100-300 EPROM 100 JFET 140-7000 CMOS 250-3000 Schottky Diodes 300-2500 Bipolar Transistors 380-7000 SCR 680-1000 Table 2: Range of device vulnerability (typical). Transient Voltage Threats and Scenarios

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