Back to Basics: ESD Basic Terms

Posted under Back to Basics, Educational, Technology on January 29th, 2023 by

To round up the ESD series, when you are going to choose your ESD protection device, you will see a lot of basic parameters that can confuse a designer. I have listed the major ones so that it makes life simpler for you when choosing ESD parts.

Maximum Working Reverse Voltage/Reverse Standoff Voltage: This is the voltage below which the diode barely conducts(Only leakage current). This is where your diode should be in normal operation. Always ensure that this voltage is above the normal working voltage of your line.

Minimum Reverse Breakdown voltage: This is the voltage level at which the diode begins to conduct and break down, typically 10-20% higher than the reverse standoff voltage. Again this value should be higher than the normal operating voltage of your circuit.

Dynamic Resistance: Its the resistance exhibited by a diode(after breakdown) when an ESD strike occurs. It’s the slope of an IV curve which you see in most datasheets. When choosing diodes, this value should be as small as possible so that the graph generated via TLP(Check prev. post) is steeper(To get a constant voltage at the output, when the current increases).

Clamp Voltage: This is the voltage that the ESD diode will show at its output due to dynamic resistance when an ESD pulse occurs. Its voltage the diode stabilises itself after the initial spike. This is very important as this is the voltage that your circuits downstream will see. Your downstream device should be able to handle this voltage for a small instance of time. This is where the problem arises as this value is usually not provided by the downstream device datasheet. You have to usually play a guessing game. Ideally, we try to get a clamp voltage as small as possible(higher than the normal voltage which it protects) when selecting ESD diodes.

Peak Pulse Current: Maximum current an ESD diode can pass before it’s damaged. It varies based on the IEC ESD protection levels a device adheres to.

Hoping this series of posts have covered the most important aspects of ESD protection, giving you a better understanding of how to choose the right ESD protection device for your circuits.

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ESD: Transmission line pulse (TLP) Testing

Posted under Back to Basics, Product Design, Technology on January 22nd, 2023 by

Continuing with the ESD series, one slightly advanced topic is TLP testing. When you design a product, you usually protect the device against ESD strikes. ESD strikes are given with an ESD gun(Think of it like a stun gun with a very short pulse width) going around and zapping the different parts of a product to see its immunity to ESD strikes. In a test lab, ESD strikes are usually done at points where a potential contact can happen. The problem with this test is that you get a binary pass or fail test report at the end of the test. This is OK for most devices but it doesn’t give you a clearer picture of what happened in a circuit in an ESD event. For eg, I want to understand what ESD current flow can the device can resist and which trace can handle what voltage etc. That’s where TLP testing comes into play.

In TLP testing, a high-voltage, high-current very short pulse is applied to the device under test through a transmission line. The device’s response to the TLP is then measured to determine its susceptibility to ESD damage. This is done by measuring the voltage and current on the device, as well as its ability to function correctly after the ESD event. TLP testing is a much more controlled way of getting repeatable tests done for ESD. TLP tests are usually used to generate the IV curves(which are very important) that you see in ESD protection device datasheets. The measurement setup needed for the TLP test is much more expensive than a typical ESD gun and hence you won’t find them in normal testing labs. TLP testing is done for the absolute characterisation of an ESD event.

For more info, I would suggest reading tech notes from the esdemc and sofics website.

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