- Compare guaranteed minimum and maximum values, not typical ones.
- Bring every value to the same conditions and units, and read the footnotes and derating curves.
- Treat a missing value as a risk: ask the supplier, never guess.
Check the datasheet before the values
- Revision and date: an old revision may not match what the factory ships today.
- Status: an “advance” or “preliminary” datasheet can still change; prefer production data for a design decision.
- Exact part number: suffixes often change the temperature grade, package, finish or screening level. Check the ordering information table: the screened or radiation-hardened variant often has different limits. Make sure every value you compare belongs to the variant you will buy.
Typical is not guaranteed
Minimum and maximum values are what the manufacturer guarantees, by test or by design. Typical values describe an average part and promise nothing. Footnotes such as “guaranteed by design” or “tested at 25 °C only” tell you which limits are not tested on every part. Compare your requirement with the guaranteed limits, over your full temperature range.
Absolute maximum ratings are not operating conditions either: they are the limits beyond which the part may be damaged. Design against the recommended operating conditions.
Same conditions, same units
Two datasheets can quote the same parameter at different temperatures, voltages, loads or frequencies. Before comparing, bring the values to the same conditions, and watch for units that look alike:
| Looks the same | Check |
|---|---|
| Gain in dB, power in dBm or dBW | Relative or absolute, and the reference level |
| Accuracy in % FS or % of reading | Full-scale accuracy is much looser at the bottom of the range |
| Pressure in bar(a) or bar(g) | Absolute or gauge |
| Drift in ppm/°C or ppm/year | Over which temperature range or time |
| Power at 25 °C or over temperature | Whether a derating curve applies |
Read the footnotes and derating curves
Derating curves, test circuits and footnotes often change the meaning of the headline number. A converter rated at 15 W may only deliver it below 50 °C; a sensor’s accuracy may exclude hysteresis or long-term drift. High-reliability projects add their own derating rules on top, such as ECSS-Q-ST-30-11C Rev.2 for space EEE parts. For high-reliability parts, the procurement specification (ESCC detail specification or SMD) overrides the commercial datasheet: compare against it.
Treat missing values as risk
If a value you need is missing, mark it as unknown and ask the supplier for characterisation data. Never fill the gap with a guess or with the value of a similar part. Keep a record of where each value came from (document, revision, page) and of the conditions you normalised to, so the comparison can be checked in a design review or an audit.
Where Procureezy fits
Procureezy reads datasheets and manufacturer pages, extracts the specifications into one comparison table against your requirements, and links its findings to their sources.