Diode Comparison: Schottky, SPA, Zener, TVS Summary 1. Diode Description 2. Diode Characteristics 3. Diode Classification & Typical Applications 4. Comparison of Diode Technologies 5. Device Parameter Comparison 6. Application Comparison Confidential and Proprietary to Littelfuse, Inc. © 2005 Littelfuse, Inc. All rights reserved. 1 Diode Description All diodes share common characteristics. They are two-terminal electrical components that allow current to flow in one direction. This behavior is called “rectification”. Today, they are mostly built from semiconductor materials (Silicon). Before semiconductors, they were implemented with vacuum tube technology. To create a diode, you must form an electrical “junction”, usually by joining two dissimilar materials. The junction in a Shottky diode is created by joining a metal with semiconductor material. Current Littelfuse diodes are formed by joining two different types of Silicon semiconductor materials (creating a P-N junction). Littefuse diodes have two primary applications: power control and overvoltage (OV) protection. Confidential and Proprietary to Littelfuse, Inc. © 2005 Littelfuse, Inc. All rights reserved. 2 Diode Characteristics There are six important characteristics of diodes: Forward Current (IF): The amount of forward current that can be continuously applied to the diode without failure. If intended for AC/power applications, this value will be specified as an average or RMS current. Forward Voltage (VF): The amount of forward voltage present when a given forward current is applied. Reverse Breakdown Voltage (VBR, VZ): OV Protection and Zener diodes are designed to take advantage of this characteristic. This value determines the limiting (or clamping) voltage presented to an application that is subject to an over-voltage event (ESD, Lightning Surge, AC Power-Cross) or, the regulation voltage for power supplies. Reverse Stand-Off Voltage (VR): Typically, the guaranteed maximum reverse voltage that can be applied without the diode going into breakdown (OV protection diodes). Reverse Current-Leakage (IR): The current-leakage when a given reverse voltage is applied (OV protection diodes). Junction Capacitance (CJ): For both power and OV protection diodes, this characteristic is undesired but unavoidable. Reducing the size of the semiconductor chip will minimize capacitance but, it will also limit current-handling capability. The value is variable and depends on the amount of reverse voltage applied. Confidential and Proprietary to Littelfuse, Inc. © 2005 Littelfuse, Inc. All rights reserved. 3 Diode Characteristics Voltage vs. Current (VI) Plot IF Forward VBR, VZ VR IR VF Reverse Common Symbol Anode Cathode Forward Current Confidential and Proprietary to Littelfuse, Inc. © 2005 Littelfuse, Inc. All rights reserved. 4 Littelfuse Diode Classifications Littelfuse Diode Class Application Remarks Conventional Diode, Rectifier Power Control Useful for “steering” high currents; converting AC to DC. Typically found in large packages such as TO-220. Power Control Useful for regulation of DC voltage in power supplies. Typically found in medium-size to large packages (Axial, TO-220). OV Protection Useful for protecting circuits exposed to high-energy events such as lightning surges or voltage transients from mechanical switching of electrical circuits (EFT). Typically found in medium-size packages (Axial, DO-214). OV Protection Diode Arrays fall into the more broad category of Silicon Protection Arrays (SPA), which are targeted for ESD protection. Typically found in small surface-mount packages (SOIC-8, SOT-23, SC-70, etc …) Zener Diode Silicon Avalance Diode (SAD), Transient Voltage Suppressor (TVS) Diode Array Confidential and Proprietary to Littelfuse, Inc. © 2005 Littelfuse, Inc. All rights reserved. 5 Other Diode Classifications or Technologies Class Application Remarks Shottky Diode Power Control Useful for high-frequency (HF) rectification required for switch-mode power supplies. Varactor Diode RF Tuning Only known application of diodes that takes advantage of the junction capacitance characteristic. Confidential and Proprietary to Littelfuse, Inc. © 2005 Littelfuse, Inc. All rights reserved. 6 Comparison of Diode Technologies Littelfuse Diode Class Reverse Breakdown Voltage (VBR, VZ) Capacitance (CJ) Remarks Conventional Diode, Rectifier 800 – 1500V Very High AC to DC power conversion Zener Diode Up to 100V Medium to High DC power regulation Silicon Avalance Diode (SAD), Transient Voltage Suppressor (TVS) Up to 600V Medium Lightning surge and voltage transient protection Diode Array Up to 50V Low (<50pF) ESD protection of highfrequency data circuits Confidential and Proprietary to Littelfuse, Inc. © 2005 Littelfuse, Inc. All rights reserved. 7 Device Application Example A Zener diode is used in this circuit to regulate the voltage of the current supply provided by V+ to the desired Vref voltage required by this IC circuit. The small size (typically DO-35, SOT-23, or smaller) and low cost of the Zener (compared to other techniques, such as a linear regulator or reference chip) make it ideal in this type of application. This solution would not work in an application with a very high V+ (forcing the device to dissipate more than 1 few watts). Application of Zener as Voltage Regulator Confidential and Proprietary to Littelfuse, Inc. © 2005 Littelfuse, Inc. All rights reserved. 8 Device Application Example A pair of Schottky diodes are used in this circuit to terminate the Vin line, typicaly a highspeed data line (USB, HDMI, PCI, etc.). The fast speed and low current draw make it ideal for active termination in these applications. Additionally, this solution provides a degree of resistance to ESD events that passive termination does not. Application of Schottky Network Termination Confidential and Proprietary to Littelfuse, Inc. © 2005 Littelfuse, Inc. All rights reserved. 9 Device Application Example D.C. Supply Protection EMI Limiting D.C. Line Protection TVS Diodes are used in a variety of general electronics/white goods circuits to provide protection from transients, regenerative voltages (“back-EMF”), and other spurious events that may damage the circuit or surrounding devices. The wide array of package high power/current handling A.C.sizes, Supply Protection (hundreds of watts), and low cost make this device very versatile in many applications. For very high transient voltages or currents (such as lightning) a more specialized device such as a SIDACtor or MOV would be desireable for maximum protection & reliability. Single Line Relay and Contactor Transient Limiting Confidential and Proprietary to Littelfuse, Inc. © 2005 Littelfuse, Inc. All rights reserved. 10 Device Application Example An SPA is used in circuits requiring multiple-line protection of data circuits from ESD and other transients that require ultra-fast (pico-second) response times and 30kV surge capability in ultra-small packages. They are also ideal for high-speed data applications such as USB and HDMI that require ultra-low (pico-farad) capacitance. The high-density packaging make it very easy to integrate into the precious board space of handheld devices. Protected circuit SP0503BAHT Application of SCR Type Array Application of Avalanche Type Array Confidential and Proprietary to Littelfuse, Inc. © 2005 Littelfuse, Inc. All rights reserved. 11