TPS562201 output sags to ~2 V and hiccups under 1.8 A load — inductor saturation?

The peak current maths above are correct, and there's a compounding effect that explains why you're seeing problems starting at 1.5 A rather than exactly at 1.8 A: soft saturation.

Most ferrite-core inductors don't have a hard cliff at their rated Isat. Inductance starts declining measurably well before the nameplate number — typically at 60–70% of the rated saturation current, depending on core geometry and material. If your 4.7 µH part's inductance is already dropping at 1.3–1.4 A DC bias, the actual ΔIL in your circuit is higher than the ~420 mA figure calculated from nominal inductance. Higher ripple means higher peak current, which pushes further into the soft-saturation region, which increases ΔIL again. The degradation is self-reinforcing.

The Isat spec on most datasheets is defined at the point where inductance has dropped 20–30% from its nominal value — so there's already meaningful degradation happening below that number, not just above it.

This is why a 1.5× derating rule is common: Isat ≥ 1.5 × Iout_max. For a 2 A application, that means Isat ≥ 3 A. It leaves headroom for soft saturation, manufacturing variation across the inductor population, and the temperature dependence of core permeability — hot inductors saturate sooner than cold ones.

When evaluating replacement parts, check for an inductance-vs-DC-current curve in the datasheet rather than just the headline Isat number. A part that shows 95% inductance retention at 2 A and rolls off gracefully is more useful than a part that claims 3 A Isat but is already at 75% inductance at 2 A.

Once you've sorted the Isat issue, check the DCR on whatever part you pick as a replacement. It becomes relevant at your load level.

High-Isat parts in compact packages sometimes achieve the saturation rating by using fewer turns of thicker wire — which increases DCR. A 4.7 µH inductor with 3+ A Isat in an 0504 or 4020 footprint can have DCR ranging from around 25 mΩ to over 100 mΩ depending on the specific part. At 2 A continuous, that spread means anywhere from 100 mW to 400 mW in resistive loss from the inductor alone.

That's not just an efficiency number. In a compact SMD package with limited copper area for thermal spreading, 300 mW of extra loss runs the inductor significantly hotter — and inductor core loss increases with temperature, which degrades inductance and pushes Isat lower. At elevated temperature, a 3 A Isat part might behave more like a 2.5 A part.

For a 5 V USB-C input supply the thermal budget is usually manageable, but it's worth cross-checking: pull the TPS562201 efficiency curve for your operating point with each candidate inductor's DCR. It's a five-minute check in the TI Power Stage Designer tool and it shows you the real efficiency and inductor temperature rise before you commit to the BOM.