See Where You are Going with Your PCB Power Distribution Network Design

January 31, 2018 Altium Designer

3D rendering: vehicle with open carbody with view at the circuitry

 

 

 

For those of you who have only experienced the brilliant high power of LED, Xenon, or Halogen headlights in today’s modern cars, you may not realize how fortunate you are. My first car was old enough that its headlights could have been candles. One year I received Halogen fog lights for my birthday, and the difference at night was amazing. Not only could I now see what was next to the car in the dark but the fog lights almost out-distanced the regular headlights as well.

 

Being able to see where you are going is important in many areas of our lives. Whether it’s going downstairs into a dark basement, driving at night, or even laying out a printed circuit board we’ve got to have the lights on. That may sound odd considering that there is usually plenty of light in our places of work and our computer monitors typically provide more than enough illumination to get the job done.

 

Previously, designing the power distribution network (PDN) has been left in the dark. Designing a PDN is much more important than its history of making sure you have a good size power and ground plane. Now as PCBs have grown in technology while shrinking in size, having a well-designed PDN has become one of the chief cornerstones of the design. A PDN analyzer can guide you through the guesswork of designing your power distribution network.

The Importance of your Power Distribution Network Design

The goal of your PCB’s PDN is to provide clean power and reference voltage to the active devices. An inadequate PDN can contribute to signal integrity issues. Also, electromagnetic compliancy (EMC) problems can be due to excessive noise on the PDN as it connects to external cables and radiates emissions.

 

It is typical for high speed designs to contain multiple power supplies, and the PDN must be designed to handle all of the different current requirements. The goal is to design a stable PDN for all the required power supplies with as low of an effective impedance as possible. This should be planned for before component placement even begins so that you know ahead of time how it should all be laid out.

 

A close up of green PCB with area fills on it

A PDN analyzer can help you find and correct PDN problems while still in layout

 

 

The Problems that Designers Face

The problem that designers face is that the planes or traces used for delivering power and ground are rarely that simple to work with. In addition to the power needs, a designer needs to make sure that the planes are adequate for signal return paths. Thru-hole devices, vias, and even slots for mechanical purposes can also punch holes in what would have been a good PDN design.

 

Another hazard to a well-designed PDN is split planes. When a designer splits a plane for digital and power ground, they need to make sure that they have the appropriate devices and signals over the digital ground. Having to split planes like this can add another level of complexity to the PDN. Additionally, buried traces will cut planes into multiple parts which is yet another headache for the design of the PDN.

 

 

 

Picture of the display of a PDN analyzer

This PCB’s PDN is displayed in a PDN analyzer

 

How a PDN Analyzer Can Help

With all of the challenges to designing a good PDN, you can see why designing a PDN could benefit from some guidance that shows the way. A PDN analyzer tool is essential in giving this guidance to you and showing you the way as you design your PCB. With a visual display of the power distribution network, PCB designers can see in real-time what potential problems are in their PDNs in order to correct them.

 

A PDN analyzer will allow you to define your power nets as sources, loads and grounds. It will also allow you to define your source and load devices. Once set up you will get a visual display of the following problems:

 

  • Excessive copper.
  • Isolated areas of copper.
  • Insufficient copper.
  • Uncontrolled voltage drops.
  • Marginal voltages at device power pins.

 

A PDN analyzer can turn up the lights in what used to be the darkness of power distribution network design and show you the way to correctly design the PDN on your printed circuit board. This will save you from having to create multiple board spins in order to identify and correct PDN problems.

 

To expertly move from schematic capture, through PCB layout, and to creating manufacturing output files consider PCB design software such as Altium Designer. Thankfully, it also contains a PDN Analyzer tool with all the functionality that we’ve been talking about here. With it, you can find and resolve PDN issues during layout before the board is manufactured.

 

Would you like to find out more about how Altium can help you with your power delivery network layout on your next PCB design? Talk to an expert at Altium.

 

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About the Author

Altium Designer

PCB Design Tools for Electronics Design and DFM. Information for EDA Leaders.

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