May. 26, 2025
Electronic Components & Supplies
Key Takeaways
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An ESD diode is a protection diode used as a countermeasure for static electricity discharge in ICs and USB lines.
The ESD diode suppresses abnormal voltages and protects downstream components in a circuit.
Low on-resistance, low parasitic capacitance, and instantaneous turn-on are some of the electrical characteristics of ESD diodes.
Electro Static Discharge ❲ESD❳ is a major issue affecting the USB data transmission rate, as well as ICs. In IC technology, the maximum rating of the components specified in a design should be satisfied in the fabrication stage. When the current and voltage applied to the IC are above the maximum rating, the components are subjected to Electric Over Stress ❲EOS ❳ due to ESD. Design engineers are constantly investigating what causes ESD and how to prevent it, as it contributes to failure and reliability issues.
Preventing ESD is key to protecting devices from damage and preventing malfunction. An ESD diode, also known as an ESD protection diode, is a protection diode used as a countermeasure for static electricity discharge in ICs and USB lines. It absorbs the abnormal voltages from interfaces or external terminals and suppresses the ESDs and transient voltage pulses.
When charged bodies come in contact, there is a sudden flow of charges which generate static electricity. The static electricity in ICs and USB lines induce voltage and current spikes that ruin the purpose of the devices. ESD protection prevents high voltages and currents generated from the ESD strike from reaching the IC or USB. ESD diodes are connected between the interface connectors and the IC in order to be protected. By placing the ESD in the signal line, the EOS is prevented from damaging the IC.
The ESD strike creates large current spikes that flow through other devices, creating a high voltage drop. If the voltage drop is above the maximum voltage rating of each component, it can cause circuit issues such as EOS, electromigration, and gate oxide stress.
The ESD diode absorbs the short-duration voltage pulses during the ESD strike. It breaks down and forms a low impedance between the interface and the IC. The high peak currents from the ESD strike flow to the ground through the ESD diode and limit the ESD strike voltages from damaging the IC or USB. The ESD diode is connected in reverse biased condition, and is operated at the region before the breakdown region.
We can compare ESD diodes and Zener diodes. In one way, ESD diodes are one kind of Zener diode, as they operate at the reverse biased condition. The ESD diode suppresses abnormal voltages and protects the downstream components in the circuit from abnormal voltages and surges, whereas the Zener diode maintains a constant voltage across components in a circuit.
ESD devices exhibit exceptional protection when they have the following features and specifications:
The operating voltage of an ESD diode is called the working voltage. The recommended practice is to select an ESD diode with forward and reverse voltage rating greater than the interface’s signal voltage. Usually, the working voltage is kept at 110% of the supply voltage.
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During the ESD strike, ESD diodes clamp the voltage to protect downstream components in the circuit. Clamping voltage indicates the extent of the ESD diode-based protection scheme. Generally, the 8 kV IEC ESD strike is approximated to 16 A Transmission Line Pulse❲TLP❳.
The low on-resistance of an ESD diode provides a low impedance path for large currents to flow to the ground, protecting the downstream components.
Like any normal diode, the ESD diode is also associated with parasitic capacitance. The parasitic capacitance should be low in high-speed interfaces to ensure signal integrity in ICs.
According to IEC -4-2 ESD waveform (8 kV), the current hits 30 A value within 0.7 to 1 ns time duration. If an ESD diode fails to turn on within this time, the ESD protection scheme does not work.
ESD protection circuits should only consume small areas. Nowadays, multichannel devices are available, offering space-saving options.
The IEC -4-2 rating gives the contact rating and air gap rating of the ESD protection device. The contact rating gives the maximum voltage rating the device can withstand when the ESD source is in contact, whereas the airgap rating deals with ESD strike discharged over an air gap. The higher the contact and airgap rating of an ESD diode, the better the protection offered to downstream devices from ESD. NFPA -77 recommended practice on static electricity is the other major standard to be considered when designing an ESD protection scheme.
The ESD clamp circuit can be used as an anti-static circuit. In this circuit, the abnormal voltage at the interface connector from the ESD strike is clamped to the power rail voltage or ground voltage using ESD diodes D1 and D2, respectively. Under normal operation of the circuit, ESD diodes D1 and D2 are reverse biased. When the input signal voltage applied at the interface connector is above the power rail voltage VDD , the diode D1 conducts. When the input voltage is less than the ground voltage, the diode D2 conducts.
High-speed communication networks, miniature devices, and integrated noise filters often get impacted by ESD. Preventing an ESD strike from damaging devices is critical, and an ESD diode is one of the best countermeasures for ESD issues. It is reported that the incorporation of ESD clamping circuits in ICs and other interfaces have drastically reduced the Failure In Time ❲FIT❳ rate of devices. If you are looking to protect numerous interfaces or ICs from static electricity discharge, include an ESD diode-based protection scheme in your circuit.
It is used to protect an IC from excessive voltage (e.g., ESD) higher than the rated withstand voltage that enters a board via an externally exposed port such as a USB port. ESD protection diodes are also called transient voltage suppressor (TVS) diodes. A slight difference between them is that the term “TVS diodes” refers to a wider range of diodes that are designed to provide protection not only from ESD strikes but also from lightning surges, switching surges, and typical signal ripples. Toshiba’s product portfolio also provides diodes for switching surge protection.
(See “Zener diode for overvoltage protection.”)
In the absence of ESD during normal operation, ESD protection diodes are invisible to a system. They are designed to conduct in the event of an excessive ESD event in order to protect an IC. In the past, Zener diodes were used for this application.
A Zener diode is a type of pn junction diode designed to be used in reverse bias. As the reverse voltage across a pn junction diode is increased, avalanche breakdown occurs at some point called Zener voltage (VZ). The Zener voltage is hardly dependent on the current flowing through the Zener diode. Therefore, Zener diodes can be used to provide a fixed reference voltage although they are seldom used for this application nowadays. Because of this characteristic, Zener diodes are also called voltage regulator diodes. The desired Zener voltage can be obtained by optimizing the dopant densities of the p-type and n-type regions that form the pn junction.
Toshiba provides an extensive lineup of Zener diodes with different Zener voltages.
It is also necessary to select the right ESD protection diodes according to the characteristics of the signal lines to be protected. For how to select ESD protection diodes, see the following FAQ entry:
Toshiba’s ESD protection diodes are available in a wide range of packages, including not only ultra-small packages with electrodes on the bottom and general-purpose packages but also flow-through routing packages that are specifically designed for USB, HDMI, and other multibit ports. In addition, semiconductor chips are fabricated using a process specifically designed for ESD protection to achieve low dynamic resistance and total capacitance. For more on these topics, see the following web pages:
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