Power Inductors Selection Guide: Specs, Packages & Top Picks

Why Your Buck Converter Probably Has the Wrong Inductor

The power inductor is the least-loved component on a DC-DC converter BOM. Most engineers take a value from the regulator datasheet's reference circuit, match it to the first available part, and move on. Then the converter runs hot, output ripple lands at 2× spec, or the supply audibly whines under load. Usually all three at once. Here's how to pick the right inductor the first time.

The Five Parameters That Matter

1. Saturation Current (Isat) — The Hard Limit

This is the current at which inductance drops to a specified percentage of nominal (usually 70% or 80%). Exceed Isat and inductance collapses, current spikes, and the converter either hits overcurrent protection or destroys the MOSFET. We've seen more than one dead supply traced back to exactly this. Always spec Isat > Iout(max) + ΔIL/2 with at least 20% margin. A 3.3V/2A buck with 30% ripple needs an inductor with Isat > 2.6A.

Temperature matters: Isat drops as the core heats up. A ferrite core rated Isat = 3A at 25°C might drop to 2.4A at 85°C. Check the datasheet curve — some manufacturers (Coilcraft, Würth) publish this, others don't.

2. DC Resistance (DCR) — The Efficiency Killer

DCR converts straight into I²R losses. At 2A output, a 100mΩ DCR costs you 400mW in the inductor alone. Dropping from 100mΩ to 30mΩ saves 280mW. The tradeoff: lower DCR means a bigger package and a higher cost.

3. Self-Resonant Frequency (SRF)

The inductor's parasitic capacitance creates a parallel resonance. Above SRF, the inductor behaves like a capacitor and the converter's noise spikes. Rule of thumb: SRF should be at least 5× your switching frequency.

4. Shielded vs. Unshielded

Unshielded (open-drum core) inductors radiate magnetic fields that couple into nearby traces and components. Shielded (magnetic-resin-coated) or semi-shielded (ferrite cap) inductors contain the field. If there's sensitive analog anywhere nearby, pay the 10–20 cent premium for shielded — the usual alternative is a re-spin. Noise-sensitive designs (audio, precision ADC) should also consider orientation: mount adjacent inductors with their magnetic axes perpendicular.

5. Package Size & Height

Power inductors are often the tallest component on the board. For space-constrained designs, watch the height: standard shielded SMD power inductors run 3–5mm tall; low-profile versions (thin-film or molded) go down to 1.2–2mm but cost 2–3× more.

Core Material Quick Reference

Metal composite cores (Coilcraft XAL/XEL series, TDK SPM series) have become the go-to for modern high-frequency converters. They combine soft saturation with low core losses and are inherently semi-shielded.

Top Series by Application

• General-purpose buck (1–5A): Coilcraft XAL4030 (4 × 4 × 3mm, metal composite, Isat up to 10A for low-µH values).
• High-current POL (10–30A): Würth WE-MAPI 5030 (5.3 × 5.1 × 3.0mm, Isat up to 25A).
• Ultra-low DCR: TDK SPM6530 (6.5 × 6.2 × 3.0mm, metal composite, DCR as low as 3.2mΩ at 1µH).
• Lowest cost: Murata LQH series (ferrite, unshielded, $0.05–0.15).
• Automotive AEC-Q200: Bourns SRP series (molded, shielded, -55 to +155°C range).
• Smallest footprint: TDK TFM series (thin-film, 1.6 × 0.8mm for 0806, under 1mm height).

Lead Time Reality

Standard ferrite SMD power inductors ship from stock at major distributors. Custom values (non-E6/E12 series) and metal composite parts in uncommon form factors can run 12–16 weeks. In 2026, the metal composite supply chain has improved but still lags behind ferrite in availability. When we order these, distributor stock often decides the part as much as the datasheet does.

Need to find the right power inductor for your next design? Search our database by inductance, Isat, and package size, or [

References

• TI Power Management Guides
• IEEE Power Electronics