I am pathetic when it comes to plumbing issues. I ran into panic mode when my sink got stuck on a holiday, where plumbers would rather take the day off than dragging their foot into my apartment. After some frantic searching online, it turned out that the plunger and a pack of baking soda are handy in getting the water to flow again.
Thankfully, I’ve never had to call a plumber for current flow issues on a PCB. While current doesn’t practically get stuck, it has its fair share of issues when you don’t practice the right optimization techniques in design.
Why Current Optimization Techniques Are Important?
Current is a parameter that is often overlooked in PCB design. Issues like EMI and power budget dominate part of the design process, but neglecting how current flows on the PCB can lead to some nasty issues.
A classic example is that you’ve got lesser power delivered to a heavy load than calculated and you spent hours wondering what goes wrong in the design. You’ll be dumbfounded when it turns out that the voltage supply trace to the load isn’t sufficient for the amount of current passing through.
The failure to predict current flow can also lead to electrical noise, particularly in mixed signals circuits. When signals of digital sources flow to its destination, the current needs to return to the source in a complete loop. The return current of high-frequency signals can sometimes interfere with analog signals on the PCB.
Current-related issues can be hard to trace even with the right tools.
Issues with currents are harder to detect compared to voltages. It’s easy to get a voltage reading on a probe on the PCB but the same cannot be said for current. Short of cutting off traces and running the current through an ammeter, it’s hard to pinpoint what goes wrong in the PCB.
Therefore, it is wiser to practice the right techniques that optimize current flow in electronic design, whether it’s to ensure efficient power delivery or to prevent electrical noise.
Optimizing Current Return Path
Electronics design is more than connecting the nets with traces on the PCB layout. If there’s anything that can save you the trouble of intra-PCB interference, it’s envisioning the current return path. Every signal that travels from a source to the receiver will need to return to the source via the ground.
For low-frequency signals, the return path is one that has the lowest resistance. However, higher frequency signals take a return path with the lowest impedance. There’s a distinction between both as the parasitic capacitance and impedance may affect the current flow in high-speed signals.
The best way to ensure that the return path does not traverse to areas with analog signals is to deliberately create the ground return for the signals. Often, having a ground polygon beneath the signal traces is the best solution. It’s also important to ensure that there are no discontinuities on the ground plane to prevent the return current introducing ground noise to other signals.
Current Optimization Techniques For Hot Spots Prevention
It’s only common sense that for power delivery to be efficient, there needs to be minimal loss across the PCB trace. Power losses sometimes manifest itself as hot spots, where a particular copper trace has to handle more current than it’s rated to carry.
Failing to optimize for current handling can make the PCB too hot to handle.
Like copper wires, PCB traces have a resistance value that is determined by the width and thickness. These parameters co-relate to the maximum amount of current that a copper trace could take before it starts heating up drastically. To avoid hotspots, you’ll need to ensure the size of the copper trace is large enough to handle the current passing through.
The efficiency of current flow is not only affected by PCB trace size but also the via that connects traces between layers. Sometimes, a number of vias are needed to successfully channel the current between layers without significant losses in heat.
An efficient power delivery network requires the current to flow unhindered, and you can achieve this using a variety of tools from the suite of layout, design, and analysis options from Cadence. It’s also useful to use a PCB design software like OrCAD PCB Designer alongside a thermal analysis tool to detect potential hot spots on the PCB.
If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.