ESD

This is Spam.

Go to the commercial section.

I'm not sure it's spam, because no actual product is mentioned. "ESD products" is not a product! But since leiditech has not given us a question to ponder, what's the point? I'll take a stab.

There are several aspects to common electrostatic discharge. First we have a quantity of charge q, built up, ready to do trouble. It's generally stored on some capacitance C, and it creates a voltage V. If V is high enough it can jump an insulated gap a find a discharge pathway. Or the charge-carrying object, such as a human body, might touch a sensitive conductor, allowing the discharge to take place. While V may not be high enough make a discharge snap, the charge q can still do damage. The question is not the source voltage, but the destination voltage resulting from the charge flow.

When leiditech says ESD products are not often used, he's completely wrong. Virtually all electronics has some form of built-in ESD suppression or protection. For example, integrated circuits have current-steering diodes to the supply rails. The discharge current is then absorbed by ground or the power-supply capacitors.

One question is how much charge can this built-in protection handle? When leiditech says ESD products, he's probably thinking of external individual ESD protection devices. These are also widely manufactured and used. Experienced engineers know and understand them well. Their purpose is to limit the maximum voltage on a circuit node by absorbing the discharge current. The type we usually encounter in electronics is called a TVS, or Transient Voltage Suppressor.

The common TVS is basically an ordinary avalanche-mode silicon zener diode, with some added metal to quickly absorb the heat generated in the silicon junction. An interesting and useful thing about avalanche is that it's practically instantaneous in action, well under a nanosecond. Rapidly-rising currents create voltage drops across wiring inductance, V = L dI/dt. But if you properly connect your wiring directly across the TVS terminals, you'll enjoy the sub-ns protection of the zener without added inductive voltage spikes.

A common-place TVS would be a 1.5KAnnn or 1.5KEnnn, where nnn is the rated breakdown voltage. For example, a 1.5KA18 will not interfere with signals to 15V, but breakdown at 18V and clamp 200A of current to no more than 25 volts. The 1.5k in the part number signifies this part can handle 1.5kW of peak discharge power, provided the half-value decay of the pulse occurs within 1ms. The 1.5KA18 costs $0.67 at Mouser. There are both smaller and much larger parts in this series.

There are two issues we might have with these simple brute-force zener-diode TVS parts: First, they have a high capacitance, which might interfere with our signals. Second, the physics behind sharp avalanche effect that they rely on does not work at low voltages. In fact, looking at the datasheet kink above, 6.8 volts is the lowest voltage Vishay offers in their 1.5KA series. And the 6.8-volt part has over 10,000 pF of capacitance at 0 volts! So, for example, if we wanted to protect say the low-voltage differential signaling (LVDS) pins potentially exposed in a USB connector, we wouldn't want to use one of these parts.

Thankfully there are a host of specialized components that have been developed to solve this issue. You can explore them at this Mouser selection page.

For example, the tiny part pictured is made by ST Microelectronics, has 8 channels, and costs $0.95 at Mouser. It's an EMIF08-0402T16, and is rated to breakdown at 16 volts. Each channel has only 18pF of capacitance at 0 volts, but it can handle the IEC 61000-4-2 level 4, which is 15kV air discharge or 8kV contact discharge. It's a 3-terminal device with 40-ohms of series resistance and its response into 50 ohms is an additional 3dB down at 300MHz.

OP opened 3 threads. The other two were blatantly spam and not in the correct category, but have been moved into the Commercial Section by Admin.