Keep shared-core coupling with the per-winding identity

Document 639 describes a coupled inductor as two inductors closely linked through a common core. The separate winding identities remain meaningful even though the magnetic structure is shared. A description of one winding consequently should not be mistaken for a statement that the device consists of two magnetically independent components. The coupling is part of the documented construction, rather than a conclusion obtainable from terminal count alone.

The note places this construction in a SEPIC discussion, while the historical LPD5010 material also names other possible circuit roles. Those examples explain why the same broad component construction can be considered in different applications. They do not establish which role a removed part served or supply a terminal assignment for an unidentified device. Product construction and implemented circuit use remain different subjects.

Keeping the per-winding identity alongside the shared core provides the basis for the later distinctions. Inductance, conductor resistance and current descriptions can refer to a particular winding or to a combined arrangement. Losing that reference would make unlike quantities appear to describe the complete device in the same way. The named-source context preserves the relationship without a winding diagram, an ideal transformation calculation or a claim of physical equivalence.

Keep connection-dependent inductance and DCR separate

The historical LPD5010 notes state their inductance on a per-winding basis. They separately describe how the reported quantity changes when the windings are considered in series or parallel. That is a connection-dependent definition, rather than permission to assign the isolated-winding number to every possible arrangement. The component's shared-core construction and the stated connection basis must remain attached to the inductance description.

DCR has its own per-winding reference in the same notes. Combining conductor paths changes the resistance description, but resistance and inductance are not interchangeable responses to that combination. One concerns the conducting paths; the other retains the magnetic relationship as well. A shortened list that carries only a single unexplained value can therefore hide two different reference questions before any application limit is considered.

The useful description preserves which quantity is stated and which winding arrangement the source associates with it. It does not reproduce the numerical series/parallel factors or instruct a reader how to connect terminals. This distinction also avoids treating the historical document's replacement notice as evidence that another part has identical present measurements. The note supplies a definition basis, while exact-product selection and actual connection evidence remain separate.

Separate leakage characterization from ordinary winding inductance

Leakage inductance is characterized under another condition in the historical series notes. Coilcraft identifies a measurement of one winding while the other is shorted. That condition is not the ordinary per-winding inductance description. Preserving it explains why two entries containing the word inductance should not be compared as though they represented the same magnetic observation.

The second winding's stated condition is central to the distinction. It changes what the characterization represents, even though the measured winding belongs to the same physical component. The result therefore needs its own name and reference rather than being substituted for the regular inductance field. A small leakage entry does not redefine the ordinary winding value, and the ordinary value does not supply the separate leakage characterization.

This is an explanation of the manufacturer's measurement boundary, without performing or prescribing that measurement. It supplies no shorting procedure, fixture, numerical leakage ratio or bandwidth inference. It also does not turn a magnetic coupling description into a safety-isolation qualification. Keeping leakage separate allows the known device's records to remain intelligible without assigning an unmeasured property to similar-looking surplus material.

Retain one-winding and two-winding load bases

The current footnotes add two distinct allocation questions. The historical saturation description refers to the sum of current flowing in both windings. A current assigned to one winding is consequently part of a shared magnetic loading condition, rather than an unrestricted allowance that can automatically be duplicated in the other winding. The reference concerns how the named criterion is reached within the coupled device.

Heating uses a different basis. Coilcraft separately describes equal current applied to both windings simultaneously and current applied to one winding alone. Document 639's named example preserves that same distinction. Heating depends on which conductor paths carry current together; a single-winding thermal entry and a simultaneous two-winding entry therefore do not describe identical loading, even before their numerical values are examined.

These references add detail beyond the general distinction between saturation and thermal current. The present question is how each criterion allocates load across the coupled windings. Keep summed magnetic loading and one-versus-both winding heating explicit, without deriving a temperature, assigning application current or copying an example value. The historical series and SEPIC example explain the bases; they do not establish a new device's rating or the condition of an offered part.

Sources and further reading

Historical Coilcraft Document 820NR LPD5010 winding/current footnotes and Document 639, revised January 2021, bounded SEPIC prose. The old replacement notice is historical context. Numerical ratios, winding maps, thermal calculations, current lifecycle and equivalence claims are excluded.