Designing with Circuit Protection at the Forethought Saves Valuable Development Time

October 21, 2015 // By EDN
Bharat Shenoy, Director of Technical Marketing, Electronics Business Unit, Littelfuse
“Smaller, faster, prettier” – these are the main criteria for today’s electronics. A profitable lead for manufacturers, but also quite challenging for design engineers, that have to fit everything together in a much smaller environment. Put safety on top of these requirements and the story is getting even more complex. Complex for both designers and manufactures and ultimately relevant for the end customers, who expect their products to be not only fully functional, but also safe.

Circuit protection is daily business

Imagine the following scenario: morning, jogging, wet weather… running shoes, hosiery, and nylon shirt. Taken together, for a brief moment, they can generate an electrostatic discharge (ESD) of 30,000V - a potential cardiac arrest for the smartphone or any other handheld device that plays your favourite music.  

Circuit protection is daily business; still, problems associated with over-voltage and over-current still remain an afterthought for most engineers. Why? Because, with their duties expanding and with design cycles compressing, most engineers relegate circuit protection to the end of the to-do list. “Faster” is the word of the day! These days, engineers have to get the form factor done, get the software done, get the prototype built, and prove out the concept. Only then, if at all, will they have time to think about circuit protection.

Saving valuable development time

The unfortunate result of leaving such matters to the last minute is that design functionality suffers. With devices getting smaller and smaller, and so many parts having to fit together, engineers can't find room anymore for circuit protection devices on their printed circuit boards. The result: they end up re-spinning the boards and losing valuable development time – time that could have been saved, had they thought about circuit protection from the very beginning. To make things worse, many times engineers do think of circuit protection, however they hurry up choosing whatever solution is at hand and the wrong protection device, resulting in functional failures, poor reliability, safety issues, shock, or even fire.

Here are some expert recommendations to guide the design engineering community in this respect:

Circuit protection from the very “chip” phase

Considering circuit protection too late in the project can really have some serious repercussions for any design engineer. One such scenario would be to put yourself in a situation where the space is not available for your ESD device. Or, even worse perhaps, you end up settling for a non-optimal location, where the device won't function the way it's supposed to. To avoid these, the best time to start thinking about such matters is after the very moment you've picked out the chip set and begun laying out the circuit board.

Understand the threats

Fuses are simple, everybody understands them, but over-voltage may not be so obvious, and people might not realize the consequences. Take lighting, for instance: people understand lightning but they may not know it travels across the ground and can create huge glitches in power lines a mile away. And this is just one example for why, knowing and understanding the possible threats is so important.

Define the needs

To accurately predict a product's circuit protection needs, the design engineer must first be able to imagine how it will be used. Once the designer understands the environment, he or she can begin making accommodations. Understanding the target environment of the product and the possible threats that might come up with that location will be crucial in selecting the right circuit protection solution. 

Know your standards

Standards determine the design of every product, all the