Analysis of advantages and disadvantages of ESD electrostatic protection components

SMF05C SOT363 ESD electrostatic protection tube 5V

A variety of ESD protection devices are currently available on the market, but the most common ones fall into three broad categories: polymers, varistors/suppressors, and diodes. The biggest difficulty in choosing the right ESD protection device is how to make it easiest to know which device provides the most protection. System vendors typically compare ESD protection devices with ESD ratings (or nominal values) in the data sheet. In fact, the ability to see the device protection system from these ratings is not critical, depending on other diode parameters.

In addition to protecting the device's ESD nominal value, the voltage value (clamping voltage) and how much current (residual current) is at the ASIC terminal is also a key factor. The ESD protection device function is achieved by shorting most of the current to ground and "clamping" the ASIC terminal voltage to a value below the pulse voltage.

Determining the clamp voltage and residual current is not an easy task. The clamp voltages quoted in most ESD protection data sheets (if included in the manual) are misleading. There is never a residual current in the data sheet because it is related to the system layout and has nothing to do with the device itself. The dynamic resistance (Rdyn) of the protection circuit as an alternative parameter helps to compare the device because devices with lower resistance can shunt a larger percentage of current. Unfortunately, this dynamic resistance value is usually not seen in the data sheet of the protection device.

Polymer device

Although polymer devices are quite attractive for high frequency applications because their subcutaneous capacitance is only 0.05 to 1.0 pF, such low capacitance can have some minor side effects. Unlike a diode, a polymer device requires breakdown when the terminal voltage reaches the trigger voltage, and this trigger voltage is much higher than the clamp voltage. A typical polymer ESD device does not break down before 500V. Once broken, it quickly jumps to a clamp voltage of up to 150V, and when the charge is released, the polymer will return to a high-impedance state. But this process can take hours or even a day, so they are not attractive for consumer applications. These devices are difficult to accurately characterize in manufacturing, and their data sheets typically contain only typical parameter values, and do not provide minimum and maximum guaranteed values. In addition, since they are physically flexible devices, their performance decreases as the number of ESD pulses is increased.

Varistor and suppressor

The varistor and suppressor are non-linear variable resistors. Although they are relatively inexpensive, suppressors typically have high trigger voltages, high clamping voltages, and high impedance characteristics such that most of the energy reaches the protected device rather than being shunted to ground. Typical low capacitance suppressors have clamping voltages ranging from 150 to 500V. The typical dynamic resistance of a low capacitance suppressor is 20 to 40 Ω. Due to its high impedance characteristics, almost all ESD surge currents are delivered to "protected" devices rather than shunted to ground.

Semiconductor diode

Another method of ESD protection is the use of semiconductor diodes. ESD protection diodes are characterized by low clamping voltage, low impedance, fast on-time and better reliability. Semiconductor diodes typically provide the best ESD protection, and today's diodes are already capable of 1pF equivalent capacitance, making them the best choice for reliable ESD protection and good signal integrity.

ESD electrostatic protection component analysis

Any protective component must appear as a high impedance circuit at the protected input during normal operation. The capacitive load it applies must be as small as possible so that it has little effect on the normal input signal. However, at the moment of overvoltage, the same device must be the primary path for energy, transferring energy away from the input of the protected device. In addition, the standing-off voltage of the protection device must be higher than the maximum signal voltage allowed by the protected terminal. Also, the clamping voltage must be low enough to prevent damage to the protected device, since the voltage at the input will be the clamping voltage of the protection device during transients.

We often see products such as ESD electrostatic protectors, ESD electrostatic resistors, ESD electrostatic dischargers, chip varistors, etc., but the most critical reference factor for protection devices should be the following three items:

Fast response time

2. Low clamp voltage

3. High current surge withstand capability

Regardless of how well the product is introduced, when choosing an ESD ESD protection component, you should still make a detailed comparison and use the IEC61000-4-2 test for verification. The current industry practice is to announce the clamp voltage based on a pulse of 8us rise time and 20us duration, while a true ESD pulse should be 1ns rise time and 60ns duration.