DC-DC Power-Module PCB Layout: 10 Rules That Usually Decide the Result

On a DC-DC supply, the schematic is only part of the job. Layout does most of the rest. The IC can be correct and the values can be calculated, and the board can still whistle, run hot, exceed ripple limits, or fail EMC. Most of those failures come from placement and routing.

The points below are the layout practices that matter on a DC-DC power PCB.

1. What the DC-DC Stage Is Doing

A DC-DC converter is a switch-mode supply that converts one DC voltage to another. The core chain is:

• Input voltage → PWM → power-switch drive → inductor energy storage → a regulated output
• Three parts decide the layout: the power loop (high current, high frequency), the sense loop (small-signal, sensitive), and the ground system

Keep the power loop short, wide, and compact. Keep the sense signal clean, away from noise, and quiet.

2. Start With the Datasheet. Do Not Invent the Layout

Beginning to route before reading the recommended layout is how the placement drifts. The sequence is:

1. Download the controller datasheet (examples include TPS54550 and TPS54350).
2. Find the Recommended Layout section.
3. Follow the vendor placement for input capacitors, the inductor, GND, and the thermal pad.

That layout has already been verified. Copying it avoids a large share of first-pass faults.

3. Placement Rule: Compact, Clear, No Crossing

Three placement sentences hold the DC-DC area together:

1. Center the layout on the power IC. Place the critical parts around it.
2. Keep input → power stage → output in one clear line of flow.
3. Keep input filtering away from output filtering so noise does not couple across.

1. Keep the main current path obvious

• Input 24 V/12 V → input capacitor → IC → inductor → output capacitor → load
• Reserve copper pour and via locations early. Do not force them in later.
• Do not detour a high-current path, do not change layers without need, and do not add extra vias

2. Keep the line compact

A DC-DC stage should sit tight:

• Parts aligned, even, and compact
• Leads short and via count low
• Critical filter capacitors against the IC pins, in the datasheet positions

Compact placement means smaller parasitics, less interference, higher efficiency, and lower heat.

4. Routing Rule: Wide, Short, Straight

1. On high-current nets, pour copper instead of drawing a thin trace

• Common ground and power input/output: pour copper first
• If a pour is not possible, make the trace as wide as possible to cut impedance and drop
• A thin trace on high current runs hot, can oscillate, and makes more noise

2. Ordinary module signal traces: 10 mil or wider

For interconnect inside the module:

• Width ≥ 10 mil
• Do not make the trace wider than the pin pad
• A wider trace handles interference and current better and solders more easily

5. Three Pins That Fail First: SENSE, GATE, INTVCC

An error on any of these three can make the supply unstable.

1. SENSE: do not tap it at the IC pin

• Function: measure the output voltage accurately
• Wrong: pull the sense line from the IC pin
• Correct:
  • Use a 0.5 mm trace width
  • Connect at the back side of the output filter capacitor
  • Stay off high-current paths and noise sources, and do not run it over a power plane

2. GATE: short, wide, away from noise

• It drives a MOSFET or an internal power switch, with high-frequency, high-current transients
• Keep the trace as short and as wide as possible
• Keep it away from the switch node, the inductor, and other strong noise sources

3. INTVCC filter capacitors: against the IC

• They supply instantaneous current to the GATE drive
• Both filter capacitors must sit against INTVCC and GND
• If they sit far away, the drive can misbehave, heat up, or whistle

6. Ground and Heat: These Two Can Destroy the Board

1. AGND and PGND

• Power ground (high current): wide, poured, with many vias
• Analog ground (sense and feedback): clean and separate
• Join them at one point near the IC so a ground loop does not form

2. No routing under the IC or the inductor

• Under the IC: leave only ground and thermal vias
• Under the inductor: do not run any signal. Magnetic coupling will pick it up

3. Thermal pad: via array plus solder-mask opening

• A PowerPAD must be filled with thermal ground vias
• Use an array so heat conducts faster
• Open the solder mask for heat and for solder wetting

7. Multiple Outputs and Inductors: Place Them at Right Angles

When several DC-DC stages share the board:

• Place adjacent inductors at right angles
• Parallel placement couples magnetically, drops efficiency, and raises noise

8. Do Not Pour Copper Blindly: Use a Thermal Relief at the Pad

A larger copper area is not automatically better:

• A large pour sinks heat quickly
• During soldering the pad cools too fast and can produce a cold joint, solder pile-up, or tombstoning

Preferred practice:

• Join a large copper pour to a pad with a cross, or thermal-relief, connection
• Leave a thermal break so the joint can wet reliably

9. Ten DC-DC PCB Rules

1. Start from the datasheet recommended layout and follow it.
2. Center the parts on the IC and keep an in-line compact placement.
3. Keep input and output filtering apart so noise does not couple.
4. Pour copper on high current. Widen any remaining thin traces.
5. Take SENSE from the back of the output capacitor and keep it off noise.
6. Keep the GATE trace short and wide, away from switch-node noise.
7. Place INTVCC capacitors against the IC.
8. Do not route under the inductor or the IC.
9. Place multiple inductors at right angles.
10. Use a thermal-relief pad connection to avoid a cold joint.

Closing

DC-DC PCB layout is not obscure. Most failures drop out when the rules and the details are kept.

• Compact placement → less interference
• Short, wide routing → less heat
• A clear ground system → lower ripple
• Adequate thermal design → longer life

On the next DC-DC board, walk this list while the parts are still being placed.