For a conventional synchronous buck converter, review the local input capacitor, high-side switch and low-side switch as one commutation loop. Check the complete path between capacitor terminals and power pins, including the ground return. A capacitor can look close to the regulator while its actual return takes a long detour. Before releasing the PCB, preserve this local connection, check the device-specific grounding arrangement, and make the prototype measurable.
This guide addresses a single-phase, non-isolated synchronous buck stage. It is a release-review workflow for hardware designers and procurement teams, rather than a complete converter design. Fly-Buck, multiphase, boost and four-switch buck-boost circuits need their own current-path analysis.
Identify the changing current path before reviewing placement
Start with two copies of the schematic. On one, mark the current path when the high-side MOSFET conducts. On the other, mark the freewheeling path through the low-side MOSFET. The branches whose current changes abruptly identify the commutation loop. In a synchronous buck, this includes the local input capacitor and both switches. The inductor current does not instantaneously drop to zero at each switching transition. TI discusses this distinction in its comparison of converter hot loops.
Do not interpret that loop as an instruction to turn both MOSFETs on simultaneously. It represents the difference between operating states. Dead time, body-diode conduction and package parasitics affect the real transition. For an integrated regulator, part of the path is hidden inside the package; review the external VIN and PGND connections against the manufacturer’s layout.
A useful review drawing
Export a top-copper view with the local capacitor and regulator references visible. Add a second view showing the adjacent reference plane. Mark capacitor positive to VIN in one color, and capacitor negative to PGND in another. Include every layer transition. This pair of views is more useful in a design review than a 3D rendering that hides copper beneath component bodies.
Place the input capacitor by terminal connectivity
TI’s SLYT614 layout application note prioritizes placement and routing of the input capacitor immediately after the IC. It recommends short, broad connections at both terminals and warns that parasitic inductance can create switching voltage spikes. Treat placement and routing as one task: a favorable footprint position alone does not establish a low-inductance loop.
For a board review, compare two candidate orientations with all copper visible. Record which one permits a direct local return without a narrow neck or an obstructing signal trace. Keep assembly spacing and the actual land patterns in the comparison. Moving a capacitor closer than the assembly process permits creates another problem; the aim is a manufacturable electrical connection.
| Review item | Evidence to examine | Reason to reopen placement |
|---|---|---|
| Positive connection | Capacitor pad to the correct power-input pins | A long branch reaches the regulator through unrelated copper |
| Return connection | Capacitor ground pad to the switching power return | Current must detour around a slot, neck or signal route |
| Layer transitions | Location and purpose of each via in the loop | Routing changes layers only to accommodate a lower-priority signal |
| Component orientation | Pad-to-pin paths, not body-to-body distance | Rotating the capacitor would materially shorten both paths |
| Assembly access | Courtyards, solder-mask and paste definitions | The proposed placement cannot be assembled or inspected as specified |
Distinguish the local loop from the supply connection
Analog Devices’ AN-139, Power Supply Layout and EMI, explains why hot-loop area and the nearby plane matter. A close, continuous plane can reduce loop inductance through electromagnetic coupling. It also cautions against treating ordinary regulator simulation models as accurate predictions of RF layout behavior.
Apply that distinction to the review package. Label the connector-side feed separately from the local commutation path. Show the stackup instead of assuming that any board described as “four layer” provides the same reference-plane spacing. Identify cutouts and routing on the layer beneath the power stage. Record departures from the reference design as specific changes that need evaluation, rather than attaching an unsupported “EMI optimized” label.
A useful sign-off question is: if another engineer follows only the marked copper, can they trace both capacitor terminals to the appropriate IC pins without guessing how the planes connect? If not, improve the documentation or the routing before approving it.
Use a bounded calculation to explain why the loop matters
Consider an illustrative transition in which current changes by 3 A in 5 ns. Assume a lumped parasitic inductance of 2 nH. Using the inductive-voltage relation, the magnitude is:
V = L × ΔI / Δt = (2 × 10^-9 H) × (3 A / 5 × 10^-9 s) = 1.2 V
If the assumed inductance becomes 5 nH with the same current transition, the result is 3 V. These are sensitivity calculations, not measured overshoot and not a prediction for the TPS62130A or any other regulator. Real behavior includes capacitance, resistance, package connections, switching control and probe loading. Ringing requires a more complete model.
The example supports a review decision: avoid adding unnecessary inductance to a fast-changing current path. It does not establish a universal maximum trace length, a guaranteed EMI improvement, or a safe operating voltage. Compare measured terminal stress with the selected part’s ratings and the project’s design margin. Record both positive and negative excursions where relevant.
Follow the exact device’s ground and sensing instructions
Do not apply a universal “split all grounds” rule. In the TPS6213x data sheet, revision F, section 11, TI requires AGND and PGND to connect directly to the exposed thermal pad and system ground. The document also calls for a dedicated VOS connection to the output capacitor, separated from the output power connection, and specifies soldering the exposed pad to the board. These instructions describe that device family, not every buck regulator.
Make a small requirements matrix for the actual part on your BOM. Include the relevant pin names, required connections and the drawing or layer where each is implemented. Check the full ordering code and package. A reference layout for a similar family name is not sufficient evidence that your pinout or grounding is correct.
Review nearby sensitive circuits as a separate pass
After the power path review, inspect feedback, voltage sensing, enable and any measurement circuitry. Ask which traces were moved when the capacitor or inductor changed position. A late placement improvement can create a new routing conflict elsewhere. Keep a before-and-after comparison, and have the schematic owner review changes that affect sensing or grounding.
Make the first prototype capable of answering questions
Define the measurements before ordering boards. For each test, name the operating condition, instrument arrangement, acceptance criterion and saved evidence. “Check ripple” is too vague to reproduce. State the input supply condition, load, bandwidth setting, probe type and measurement location. The engineer responsible for verification should choose an appropriate probing method for the voltage and switching speed.
| Question | Record | Review outcome |
|---|---|---|
| Are switching stresses acceptable? | Waveforms, probe setup and operating conditions | Compare with device ratings and project margin |
| Does the rail behave across load changes? | Load-step definition and output response | Compare with the powered circuit’s supply requirements |
| Does the assembly run within its thermal budget? | Ambient conditions, load and temperature measurement method | Evaluate the product enclosure and cooling assumptions |
| Are emissions acceptable? | Applicable test configuration and pre-compliance results | Identify remaining formal compliance work |
Keep measurements linked to the assembled revision and BOM variant. A waveform from an earlier capacitor value or a hand-modified prototype should not silently become evidence for the production configuration. If a change improves one measurement, repeat the affected operating corners before closing the issue.
Release the board with an auditable manufacturing package
The following is a proposed engineering workflow, not a certification requirement. Assign an owner to each unresolved item and distinguish layout approval from electrical verification. Manufacturing files describe what to build; they do not prove that a power stage meets its system requirements.
- Freeze the schematic, layout and BOM under matching revision identifiers.
- Attach the marked input-loop views and identify the reference design used for comparison.
- Confirm the input capacitor’s exact manufacturer part number and document how any alternative will be reviewed.
- Review the actual stackup and copper features against the approved PCB design guidelines.
- Include fabrication data, assembly drawings, placement coordinates and the BOM according to the assembly file preparation guide.
- Record unpopulated options, deliberate rework and any measurement access needed on the first build.
- List the tests that remain open before production approval.
For a manufacturing inquiry, provide the board revision, quantity, fabrication requirements and assembly files, plus any power-stage placement constraints that must survive a DFM change. Use the project inquiry form to discuss the build package. Keep circuit-performance approval with the responsible design and verification team.
Frequently asked release questions
Is there a universal capacitor-to-IC distance?
No single distance captures the complete connection. Review the selected device’s recommendations, both terminal paths, package geometry, stackup and manufacturable placement. A distance measured between component centers is particularly weak evidence.
Can a schematic check approve this loop?
A schematic check verifies intended connectivity. The release review must also examine the implemented copper and return paths. Save both types of evidence so that an electrically correct netlist is not mistaken for a completed layout review.
What should purchasing do when a capacitor is unavailable?
Request an engineering-approved alternative rather than approving by nominal capacitance and footprint alone. Keep the approval tied to the BOM revision, and record whether the substitution requires renewed verification. Purchasing should not have to infer power-stage equivalence from a distributor description.