Power Distribution Network Design Guidelines

We are talking about signals, impedance, and differential pairs a lot in articles. Yes! Propagation of the signal is not easy; we need to follow a lot of guidelines. And in all this, people forget about power integrity, and you know what, without good power integrity, the signal performs worse. Without a good Power Distribution Network (PDN), your signals might as well be doodles on copper.

In this article, we’ll explore PDN design guidelines from a PCB perspective. We will see what a good PDN actually means. By the end, you’ll see that power delivery is not just plumbing, but it’s precision engineering.

What Is a Power Distribution Network (PDN)?

A Power Distribution Network (PDN) is the system of planes, traces, vias, decoupling capacitors, and regulators that delivers power from your source to the main ICs on your PCB. Power to the IC is the most crucial part of the PDN because if there is any drop in the path, they would not get enough current, and the voltage drop across the ICs increases, which results in false operation.

Power distribution is not only from the source to the voltage regulators, but also from the voltage regulator/PMIC to the main circuit. The decoupling capacitors also play an important role in the PDN. So a power distribution network chain consists of:

Input connectors > voltage regulator/PMIC > decoupling network > power planes > Main IC > ground return paths > decoupling capacitors.

Why Power Integrity Matters

Power Integrity (PI) is the ability of the PDN to provide a clean, stable, low-noise voltage to all ICs across all operating conditions. Why it matters:

• Voltage droop: When ICs demand sudden current, the supply voltage can dip, which can cause logic errors. But with the proper decoupling and bulk capacitors, we can tackle the issue.
• Ground bounce: Return currents can shift ground reference levels, corrupting signals. In this case, the ground is no longer at 0V but at some voltage like 0.1V.
• Noise coupling: Switching noise in the PDN can radiate as EMI or sneak into sensitive analog circuits. This type of problem is widely faced in buck/boost converters.

PDN Design Goals (and How to Achieve Them):

1. Low Impedance Path

Keep PDN impedance below a target value for e.g., <50 mΩ across operating frequencies. This can be measured using the characteristic impedance plot. High impedance means higher voltage fluctuations under load, which makes the PDN even worse.

In the PCB, it is suggested to use solid power planes instead of long traces and short, and direct return paths with them.  Widen traces that carry high current, which can be calculated in any online software or Python-based open source code made by JLCPCB.

2. Stable Voltage (Minimize Droop)

Every IC requires a stable input voltage supply to make it work within ±3–5% tolerance. This type of data can be found in the electrical characteristic column of the IC datasheet. If the guidelines are not met, a small droop can cause logic misfires in modern ICs. For example, if there is a sudden load change, the charge must be supplied all the way over from the main source. That’s why bulk capacitors are required to hold the charge locally. If supplied from the source, the overall inductive load increases and hence causes decoupling problems like second-order effects, including voltage overshoot and decay.

In the PCB, it is suggested to place at least one bulk capacitor at the power entry points (low-frequency stability). And other ceramic decoupling capacitors near IC pins (high-frequency transients). Multiple capacitors mean it will cover a wide frequency range. But there are some proper guidelines to choose the value of capacitors, which can be found in the “decoupling and resonance” article by JLCPCB.

3. Noise Suppression

Modern ICs work in the GHz range; the data can be easily corrupted if there is any noise. Moreover, the switching converters can provide a stable voltage but with high-frequency ripples.

In the PCB design, we need a mix of capacitor values (e.g., 0.1 µF, 1 µF, 10 µF) with low ESL and ESR. All this is not only for the power line but also to suppress the noise of any other source connected to the rails.

4. EMI and Ground Bounce Control

If there is no good power delivery, then the return paths are also not good. This causes unwanted emissions and ground shifts. High currents returning through poor paths create EMI and bounce.

In the PCB design, to avoid this issue, we always provide a continuous ground plane without any splits. Power and ground planes are tightly packed in the prepreg layers, one over the other. All this is to suppress the electromagnetic field entering from one layer to another.

PCB Layout Strategies for PDN

Capacitor Placement:

• Closest possible to IC power pins.
• Multiple values for broadband coverage.
• Spread across the board to avoid hot spots.

Via Design:

• Use via-in-pad for critical decoupling.
• Avoid long via stubs (they add inductance).

Power Domains:

• Separate analog and digital supplies.
• Isolate noisy high-current rails from sensitive ones.

Return Paths:

• Never cut the ground plane under high-speed signals.
• Ensure uninterrupted return paths.

Tools and Simulation for PDN Design:

A better PDN can be realized by simulating the design with the chosen stackup. Methods like Target Impedance,

in which we define the maximum allowable impedance (Ztarget). The PDN impedance should stay below Ztarget across frequencies for optimal performance. It can be simulated using the software multiple times to get a better-matched profile.

Tools: Keysight ADS, Ansys SIwave, Cadence Sigrity.

Design Example: PDN for a High-Speed FPGA Board:

Imagine designing a PCB for an FPGA core rail (1.0 V, 40 A, GHz switching).

• Bulk Capacitors: Near VRM to handle slow transients.
• Mid-value Caps (1 µF, 10 µF): Spread near the FPGA.
• Small Ceramic Caps (0.01 µF, 0.1 µF): Directly under FPGA pins.
• Stack-Up: Power and ground planes closely paired.

A good stackup for the better SI/PI can be:

• Top — Signal (component side)
• L2 — Ground (solid)
• L3 — Power (all supplies; split into islands if necessary)
• L4 — Power (or plane split for other voltages)
• L5 — Ground (solid)
• Bottom — Signal (solder side)

This ensures short return paths, embedded decoupling, and low EMI.

Conclusion:

Signals may get the spotlight, but without a solid Power Distribution Network, they’ll crash like a rock band with no electricity. The PDN is the silent hero of PCB design, ensuring that every IC gets clean, stable, noise-free power. A summary of PCB design strategies according to the required design goals is given below:

Using the guidelines and effective strategies mentioned above, you can design a better PDN. Moreover, you are free to simulate the designs. For more JLCPCB design engineering team is always there and keeps spreading the awareness on these types of topics.