Designing your PCB for Optimal Power Integrity

February 5, 2019 , in Blog

Once or twice, I have been accused of being a bit geeky. I suppose that is because of my fascination with science and mathematics, which is married to my belief in humanism. Perhaps, this explains my love of television shows like MacGyver where a mere human is always able to utilize science and technology to get out of a seemingly impossible jam. The lesson that I take away from these situations is that not all scenarios have the same solution, but that there is always a solution. You just need to know when and how to apply that solution.

PCB measurement and analysis

When designing a PCB, particularly when multiple signal types and power scenarios are involved, you are faced with the dilemma of finding the right power integrity solution for your board. Although power is an electrical signal property, power integrity is not to be confused with signal integrity. However, both are important to your board’s operation and their optimization should be included in your design objectives. But before discussing ways to optimize power integrity, let’s first explore its impact on your design.

What is PCB Power Integrity?

Power integrity can be defined as the assurance that an electrical system and all of its elements have the needed power such that operation can occur adequately or as intended. For design and analysis, this requires not only supplying adequate power to active components but also maintaining power levels and minimizing losses of all signals that your board processes. From the former perspective, your PCB can be viewed as a closed electrical system with a power distribution network (PDN). To achieve power integrity, all components or modules must be supplied with power at the level required for operation, which is not simply making sure that voltages are at, or above, an acceptable level. The major threat to power integrity for your PDN involves line variations or transients from your power supply that may cause fluctuations in the quality of your power profile.

During operation, the latter perspective must be included as the situation is even more complicated by the introduction of input and output signals. Digital circuitry is dependent on your components ability to distinguish between highs and lows (typically near 5V and 0V, respectively) and signal duration. The latter means that transitions or rise and fall times must also be properly recognized. Additionally, analog signals have an inherent frequency component that, in conjunction with amplitude, defines the quality of the signal and must be maintained. For frequency dependent signals, major concerns include external interference or noise and shifts along the transmission path that may result in distortion.

Today, PCBs are typically small and densely packed with components. This closeness of components, especially between signal traces and power paths can be a source of electromagnetic interference (EMI) or noise for your signals and impact power signal stability. In most cases, your boards are comprised of one or more high power components that require power dissipation to prevent adversely affecting other board elements. Optimal management of your power integrity requires that these higher frequency RF signals are isolated from your PDN. To a great extent, the power integrity of your board depends upon your application of design techniques and choices for its manufacture to mitigate these potential issues and promote power and signal integrity.

Optimal PCB Power Integrity Design

Managing power integrity on your PCB can be viewed as designing your board such that power supply output variation is minimized, interference between traces and the PDN is minimized and power losses and dissipation are adequately managed. These objectives can be simultaneously achieved by employing the following tips into your design process.

Power Integrity Design Tip #1: Make good use of capacitance and filters

Capacitance can be used to improve power integrity in a number of ways. First, the PCB stackup materials should be chosen to manage the board capacitance across a range of frequencies. Bulk capacitors can also be also used to mitigate voltage drops due to trace inductance. Additionally, decoupling capacitors may be placed between adjacent signal paths to minimize interference. Filters comprised of capacitors, inductors and resistors should also be used to remove harmonics and quickly dampen frequency variations from switching circuitry.

Power Integrity Design Tip #2: Utilize trace parameters to control route impedances

Controlling the impedance on power traces is critical. The best way to control impedances is by manipulating PCB trace width and copper thickness.

Power Integrity Design Tip #3: Use separate grounds for digital and analog signals

Just as components and traces should be isolated according to signal type, so should your grounding. This may require that your PCB stackup include multiple ground planes.

Power Integrity Design Tip #4: Use regulators on power supply inputs

Your PDN is vulnerable to fluctuations from your power supply. You should utilize voltage or current regulators to minimize the ripple effect of these variations and stabilize the power to board components.

Power Integrity Design Tip #5: Select materials to help control impedance  

One of the major decisions that impact your power integrity is board impedance, which is determined by your choice of materials.

By following the tips listed above, you will be able to optimize the power integrity for your design.

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Power integrity is a significant issue and should be addressed as part of your PCB design. At Tempo Automation, the industry leader in fast turnkey PCB manufacturing, we utilize a wide range of materials, enabling us to meet the impedance needs for your specific board type. We will work with you to ensure that your design requirements can be instituted.

And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium user, you can simply add these files to your PCB design software.

If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on power integrity or how to design for its optimization on your board, contact us.

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