[Technology World] ESD protection starts from your fingertips
Latest update time：2021-09-03 19:04
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With the increasing number of portable, wireless and wearable devices, the potential for field failures caused by exposure to electrostatic discharge (ESD) is also increasing. The most common cause of ESD is friction between two dissimilar materials, resulting in a buildup of charge on each surface. Often, one of those surfaces is the human body itself, and it is not uncommon for this static charge to build up to 15,000 volts. An ESD event with a static voltage of 6 kilovolts is enough to cause pain. While lower voltage discharges are sometimes unnoticed, they can still cause catastrophic damage to electronic components and circuits. Each new access point on an electronic device multiplies the risk of damage by creating an electrical path for high potential currents to enter the device itself. Whether these sensitive electrical devices can survive these insults depends on comprehensive circuit protection.
When performing an ESD tolerance analysis on a typical handheld device, each data or power interface can serve as a pathway for ESD to enter the system. Necessary breaks in component body insulation and shielding are also opportunities for transient intrusion. The goal of any effort to mitigate ESD damage is to "clamp" or limit the ESD transients that enter the device to non-destructive levels. Silicon transient voltage suppression (TVS) diodes and diode arrays are the most effective ESD protection technologies available.
Headphone jack
An ESD discharge near the headphone port may travel into the interior of the device and arc through the speaker circuit. Due to the very low signal speeds seen on such circuits (< 20 kHz), a high capacitance suppression device (i.e. greater than 20pF) is recommended.
Keyboard/Buttons/Switches
These simple components provide a path for ESD to enter the board if the transient arcs from the switching structure to the board. Because they are essentially DC lines, a high capacitance (such as 30pF) suppressor is recommended.
Power port
This low voltage input is used to charge the battery and provide direct power to the circuit. As a true DC circuit, a high capacitance suppressor is recommended.
I/O Ports - Edge Connectors
The first factor to consider when protecting this signal port is the data rate of the signal. As data rates increase, it is critical to consider the capacitance of the selected suppressor to avoid causing any signal integrity issues in the system. For example, circuits running at low speeds on this port can be protected using higher capacitance TVS diode arrays or devices with tens of picofarads.
For very high data rate protocols such as USB 3.0 or HDMI 2.0, select suppressors with very low capacitance so that the system can transmit and receive data without loss of signal quality due to the protection device.
TVS diode arrays provide a high level of protection against ESD, electromagnetic interference (EMI), and lightning strikes. These devices work in two ways. First, they absorb transients with diodes, direct the current, and then an avalanche or Zener diode clamps the voltage to an acceptable level. Under overvoltage conditions, the device must have a low clamping voltage at a specified current waveform to protect sensitive integrated circuits and ports. In normal operation, the reverse isolation voltage must be higher than the supply/operating voltage of the device and should have low leakage current to prevent power supply loading. The device's capacitance must be low enough to reduce distortion of the input signal. The device's package must have a small footprint and low height to save space in high-density circuit board layouts. The device must also be able to withstand multiple ESD pulses as specified in IEC 61000-4-2. Other key characteristics, such as the number of lines protected, ESD immunity, and footprint, also need to be considered.
Weighing all of these considerations to select the most appropriate TVS diode array for an application is made easier with the help of Littelfuse's iDesign™ online simulation and product selection tool. Circuit designers can enter system and device parameters and then select up to three TVS diodes for comparison. Using the built-in simulation tool, these devices can be compared on how they will perform in an application without building a prototype. To use the iDesign online tool for free, please register at http://www.littelfuse.com/idesign.
To learn more about how to use the iDesign online tool, please watch the Speed2Design iDesign video tutorial: https://www.speed2design.com/idesign-videos/
Chad Marak is the Director of the Semiconductor Business Unit at Littelfuse. He has been involved in the circuit protection industry since 2002 and joined Littelfuse in 2007 as an analog design engineer. His current responsibilities include providing strategic guidance for the development of the Semiconductor Business Unit. He holds a bachelor's degree in electrical engineering from Texas A&M University and a master's degree in electrical engineering from Santa Clara University. He has 12 years of experience in the semiconductor industry and holds four U.S. patents.
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