Thermal Design
Thermal Resistance and Derating Datasheet Comparison
How to compare thermal limits when datasheets publish package resistance, ambient conditions, board assumptions, and derating curves differently.
Why this comparison matters
The source context determines whether values can be compared.
Thermal resistance can change with board copper, airflow, package, interface material, and mounting method.
Power ratings are often conditional and may not apply at the same ambient temperature.
Derating curves can be more useful than a single headline rating.
Common datasheet labels
Labels and aliases to preserve before mapping.
Unit normalization
Normalize only when the unit family and condition are compatible.
| Property | Source formats | Canonical format | Review note |
|---|---|---|---|
| Thermal resistance | C/W, K/W | deg C/W | Comparable only for the same thermal path and package condition. |
| Temperature | F, C, K | deg C | Keep ambient, case, junction, storage, and operating limits separate. |
| Power | mW, W, kW | W | Compare with derating condition and duty cycle attached. |
Worked comparison example
Originals first. Normalized values second. Review last.
| Spec | Sheet A Original | Sheet B Original | Sheet A Normalized | Sheet B Normalized | Review |
|---|---|---|---|---|---|
| Operating temp | -40 to 125 C | -40 to 257 F | -40 to 125 C | -40 to 125 C | Equivalent after conversion |
| Thermal resistance | 28 C/W JA | 22 C/W case | 28 C/W JA | 22 C/W case | Different thermal path |
Review warnings
Values that should not be accepted automatically.
Do not compare junction-to-ambient and junction-to-case values as equivalent.
Do not treat absolute maximum temperature as a recommended operating condition.
Preserve airflow, board area, copper thickness, and mounting assumptions when available.
How SpecCore handles this
Formula-first comparison output for engineering review.
SpecCore keeps thermal path labels, temperature conditions, power units, and review warnings visible so equivalent-looking thermal numbers are not accepted without context.
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