1001 Technical Article Only One Name Means ProTek’Tion™ Transient Voltage Suppression Diodes By: Ivan G. Lawson Silicon TVS diodes contain a P/N junction similar to a Zener diode but with a larger cross section, which is proportional to its surge power rating. These diodes are clamping devices that limit voltage spikes by the low impedance avalanche breakdown of the P/N junction. The V-I curve shown in Figure 1 is similar to that of a Zener diode. TVS diodes are designed and characterized for transient voltage suppression, while Zener diodes are designed and specified for voltage regulation. CURRENT I IFPP + P-N - IF Vc BV VR VOLTAGE V IR VF - P-N Deciphering TVS Electrical Characteristics • Stand-Off Voltage (VWM) - the maximum continuous dc or peak voltage which may be applied over the standard operating temperature range. VWM is normally 10% below the breakdown voltage (VBR). • Breakdown Voltage (VBR) - the voltage measured across the device at a specified pulsed dc current (IT or IBR) on the V/I characteristic curve at or near to where the breakdown (avalanche) occurs. Also known as the voltage across the device in the breakdown region prior to the switching point at a specified breakdown current (IBR). • Leakage Current (ID) - the maximum current that flows through the device at the rated stand-off voltage (VWM) for a specified temperature. Also known as Reverse Leakage Current (IR). • Capacitance (C) - this parameter is associated with high data rate applications and is measured at specific frequency and bias. High capacitance degrades signals. • Forward Voltage (VF) - the voltage across the device in the forward conducting state at a specified current IF. • Clamping Voltage (VC) - The peak voltage measured across the device during the application of a pulse current (IPP) for a specified waveform. Note that Leakage Current and Capacitance should not effect the performance of a circuit. + Suppressor Types IPP Figure 1. Unidirectional V-I Curve Clamping Devices Longer duration pulses can be suppressed by the TVS diode by increasing the die size and head dissipation. Both voltage and power capability can be increased by stacking parts in series or parallel. A transient is clamped instantaneously and diverts the damaging current away from the protected device. Figure 2 shows a transient current being diverted to ground. 8kV Positive and Negative Transient Suppressors limit voltage spikes to tolerable levels by either clamping or crowbar action. A suppressor that clamps, begins conducting when its threshold voltage is exceeded, then restores to a non-conducting state when the voltage drops below the threshold. Voltage spikes are clipped off to safe level through clamping. Transient Voltage Suppressors are examples of clamping devices. There are two major categories of clamping device: a) those that attenuate transients, thus preventing their propagation into a sensitive circuit - Standard TVS Arrays as shown in Figure 6. VOUT VIN 1 1 2 UNIDIRECTIONAL 2 BIDIRECTIONAL I1 I2 12V Positive and 0.6V Negative Clamped Waveform for Unidirectional Device Figure 2. Unidirectional Device (Asymmetrical Clamping) 1001.R1 4/11 Figure 6. TVS Diode Array - GBLC Series Page 1 www.protekdevices.com 1001 Technical Article Only One Name Means ProTek’Tion™ b) those that divert transient away from sensitive loads, so limiting the residual voltages - Steering Diode Arrays as shown in Figure 7. 1 7 2 6 3 IPP - Peak Pulse Current - % of IPP 8 120 5 4 40 td = t/(IPP/2) 20 0 RTip e-t 60 Crowbar Devices TIP TEST WAVEFORM PARAMETERS tf = 8µs td = 20µs Peak Value IPP 80 Figure 7. Steering Diode Array - DALC112S1 Crowbar devices conduct when threshold voltages are exceeded and then trigger to an on-state voltage drop for only a few volts, hence the name “crowbar”. These devices restore to a non-conducting state when the driving voltage and/or current is reduced with the passing transient. Examples of crowbar devices are Gas Discharge Tubes (GDT) and Thyristors. Figure 8 shows metallic and longitudinal protection using Thyristors (TSS). tf 100 0 5 Front Time 10 15 t - Time - µs 20 25 30 Fall Time Figure 4. 8/20µs Pulse Waveshape A TVS diode can have a peak pulse power rating (PPP) ranging from 30 kilowatts to as low as 25 Watts. The power rating is derived from the product of the peak pulse current (IPP) and the clamping voltage (VC). Figure 5 shows a 400 Watt 8/20µs rated curve. As the surge pulse width decreases the peak pulse power increases logarithmically. For shorter pulse widths, the TVS can handle higher peak pulse currents. 10K PPP - Peak Pulse Power - Watts To Protected Equipment 1K 400W, 8/20µs Waveform 100 RING 10 0.1 RRing 1K 10K A 3µs surge will have a peak pulse power of approximately 1kW. When the surge pulse is increased, as in the 10/1000µs curve, the peak pulse power will decrease to 60 Watts. Package Configurations Waveform Characterizations TVS diodes are available in a variety of sizes from large modules to minature surface mountable flip chips. These devices protect single to multiple line applications in unidirectional or bidirectional configurations. Most TVS diodes, which are used in low power protection applications are specified according to an 8/20µs waveform as shown in Figure 4. Higher power applications are measured with the 10/1000µs surge waveform. 1001.R1 4/11 10 100 td - Pulse Duration - µs Figure 5. Peak Pulse Power vs Pulse Time Figure 8. Metallic and Longitudinal Protection - Thyristor (PP-SM Series) Three equal TSS devices are used in this application for metallic (tip-to-ring) and longitudinal (tip-to-ground and ring-to-ground) protection. 1 Page 2 www.protekdevices.com 1001 Technical Article Only One Name Means ProTek’Tion™ company information COMPANY PROFILE ProTek Devices, based in Tempe, Arizona USA, is a manufacturer of Transient Voltage Suppression (TVS) products designed specifically for the protection of electronic systems from the effects of lightning, Electrostatic Discharge (ESD), Nuclear Electromagnetic Pulse (NEMP), inductive switching and EMI/RFI. With over 25 years of engineering and manufacturing experience, ProTek designs TVS devices that provide application specific protection solutions for all electronic equipment/systems. ProTek Devices Analog Products Division, also manufactures analog interface, control, RF and power management products. 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ProTek makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does ProTek assume any liability arising out of the application or use of any product or circuit and specifically disclaims any and all liability without limitation special, consequential or incidental damages. LIFE SUPPORT POLICY: ProTek Devices products are not authorized for use in life support systems without written consent from the factory. 1001.R1 4/11 Page 3 www.protekdevices.com