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Slope of the line is crucial to ESD protection

Posted: 31 Mar 2014     Print Version  Bookmark and Share

Keywords:ESD  USB  LCD TV  SP3031  suppressor 

As the components employed in high-quality electronic products, televisions for instance, continue to shrink, the circuitry becomes increasingly more sensitive and difficult to protect because of the deep sub-micron silicon processing used to create them. Transient over-voltage events can then cause soft, latent or even catastrophic failures.

Electrostatic discharge, more commonly known as an ESD event, represents a common, over-voltage transient. And, in fact, modern ICs are generally equipped with a minimum level of ESD protection to safely survive the manufacturing process. However, the level is typically very low (i.e. 500V) and the ESD test model used is nothing like what can be seen in the field while the application is in the hands of the user. As a design engineer, it is important to note that significantly higher ESD levels can be generated during day-to-day use of their product. For instance, humans can generate ESD levels in excess of 15kV simply by walking across a carpet. If an ESD event of this severity is discharged into a USB port, for example, it can severely damage on-chip protection circuits and the circuitry they are meant to protect. This would then render the USB useless.

Figure 1: ESD current paths for a generic I/O port.

Protection for sensitive ICs needed
A case in point illustrates how closer collaboration between global electronics manufacturers and their component supplier can be the key to developing solutions to these problems: Last year, a market-leading manufacturer of consumer electronics, mobile communications and home appliances contacted Littelfuse to help them solve a potentially serious problem. They determined that a key IC was experiencing frequent damage via the USB port. The IC in question was used to make an LCD TV smart by providing WiFi connectivity. The company had already tested many different devices and only been able to obtain a maximum of 3.5kV with respect to the systems ESD immunity. None of the ESD solutions from other companies had been able to meet their requirements for protection. After investigating the design and understanding the target ESD immunity levels, Littelfuse confirmed that it could in fact provide a device capable of meeting their needs.

Figure 2: Graphical representation of dynamic resistance.

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