Engineers and circuit designers typically look at power and data bus protection last in their design process. Most of us are guilty of this at one time or another. It happens; we are busy and focused on designing and implementing the main function of the system. When we are almost done, we find out that our system must meet certain protection requirements for exposed ports such as USB, SATA, HDMI or VDSL. Most of these requirements are driven by international or local compliance standards where the equipment is targeted to be used/sold, hence mandatory. Well, sweat no more! If you need to design protection for your application in a hurry , we recommend that you read on.
Bourns has been working with circuit designers for many decades to solve their circuit protection needs. During this past decade, we saw a growing demand for simple, yet complete protection solutions. We also know that engineers need to be able to quickly build reliable protection into their systems during the prototype stage to test and further optimize to their final requirements.
That’s why Bourns® PortNote® Solutions were developed: To accelerate our customers’ system design and shorten time to market of their final product.PortNote® Solutions outline a simple, yet complete protection scheme in an easy-to-read one-page document. PortNote® Solutions have been helping designers for more than seven years now. Its popularity has grown over the years and now includes39 PortNotes covering applications in telecom, consumer and industrial market segments. More are being added and updated for relevance to latest compliance recommendations and newer products.
How to get the most out of a PortNote® Solution
Now that we have described what PortNote® Solutions are, let’s dive into how to make the best use of them in jumpstarting your protection design. Figure 1 is an example of a popular PortNote®Solutions for the RS-485 interface.
The RS-485 interface is used widely in the industry across many applications in the industrial, communication and consumer space. Let’s say that you are using a RS-485 link in your system that runs outside the building and is, thereby, exposed to both inductive and lightning surges. The best place to start in this RS-485 PortNote® Solution is to look at the compliance section (Box 2 in Figure 1). Listed are the most common compliance standards that this PortNote® Solution targets to meet or exceed. For example, IEC 61000-4-5 relates to lightning and industrial surges caused by power system switching transients and lightning- induced voltage and current surges.
One can easily identify if their system compliance requirements can be covered by the standards listed in the PortNote® Solution. If they aren’t, we invite you to check with a local Bourns field team member or customer support line for further clarifications.
Next, study the recommended protection solution (Box 4). This diagram (also shown in Figure 2) forms the backbone of this PortNote Solution to achieve surge protection for RS-485 at the compliance levels listed in Box 2.
The Bourns engineering team that develops PortNote® Solutions for a given interface or power system has many years of hands-on experience, helping customers design their individual protection solution to meet or exceed their target protection requirements. If any problem is discovered or a customer has a question during the review or implementation of a protection design, as shown in a PortNote Solution, our field and factory teams are ready to help resolve them.
One final, yet important point about a PortNote solution– it is not optimized. The goal is to make sure that our customers startwith a solution that meets or exceeds their compliance test requirements. If there is concern on protectionBOM cost or board space constraints like in USB or SATA ports, further testing may be needed with other equivalent components.
As an example, in the RS-485 port protection, Bourns® TBU® High-Speed Protectors (HSPs) provide excellent current limiting during surge events. However, TBU® HSPs are active components, and typically, will occupy more board space than a passive component such as a power resistor. In some cases, a power resistor may be a more cost-effective option and a smaller substitute as long as surge levels are less severe. It’s all about making the right “trade-offs” for a given application, and we leave this to our customers However, we do make some alternate recommendations that are shown in Box 3.
Procrastinating on a port protection design will no doubt continue given the complexity of today’s highly integrated applications. To help streamline the task, Bourns has a growing resource library of PortNote Solutions that can really help expedite this often last, but important part of the design process.
Please check out our current PortNote Solutions library here. If you have request for a protection scheme that is not covered in this list, please do not hesitate to contact Bourns customer service.