Contact Us
Contact

Crystal Matching Guide

Match a Crystal in Three Steps

A repeatable verification process to ensure parameter compatibility and circuit stability before your final board layout.

01

Extract IC Specifications

Review the target MCU, MPU, or ASIC datasheet to locate the following parameters within the oscillator section:
  • Load capacitance (CL). Usually listed as "CLOAD" or "CL" in the crystal oscillator chapter. Common values: 6 pF, 8 pF, 9 pF, 10 pF, 12.5 pF.
  • Oscillator stage type. Pierce (single inverter) is the most common. Some ICs specify Colpitts or differential. This determines the external capacitor topology.
  • Target frequency. Fundamental mode or overtone? An IC spec'd for 24 MHz fundamental needs a different crystal cut than one designed for 3rd-overtone operation.

02

Verification Calculations

Use the extracted values to verify three critical circuit margins:

  • Load capacitance match.
CL(ext) = 2 × (CL(target) − C(stray)) [assume C(stray) ≈ 3–5 pF] Each external capacitor (CL1, CL2) should equal CL(ext). If your IC has a programmable internal load capacitor array, set it to CL(target) directly.
  • Gain margin.
|R(neg)| ≥ 5 × ESR at the crystal’s specified frequency. The IC’s oscillator stage must provide enough negative resistance to overcome the crystal’s equivalent series resistance — with margin. Measure at the highest operating temperature, where gain is weakest.
Or skip the math — our matching calculator does both checks.
  • Drive level.
The IC’s oscillator output power must stay below the crystal’s maximum drive rating. This is especially tight for tuning-fork crystals. If the IC drives harder than the crystal can handle, add a series resistor to limit current.

03

Component Selection

Filter the FCom crystal portfolio using the calculated CL and target frequency to identify compatible part series.
Ask for Catalog

The Tools. The Catalog. And A Direct Line to Our Engineers.

Download what you need. Upload your spec. We’ll handle the rest.

Resources

Resources

Fcom Product Catalog

Full crystal and oscillator portfolio with electrical specs, mechanical drawings, and ordering codes.
View More
Drag & Drop Files, Choose Files to Upload You can upload up to 5 files.

Error, invalid data format. please fix the data format and send again. thanks!

Recommended External Capacitor (Cext) (pF)≈

Didn't Find A Match? That's Not A Dead End.

Three paths forward when off-the-shelf crystals don’t line up.

Your CL falls outside standard crystal values.

The target load capacitance from your IC datasheet doesn’t match any crystal in the standard portfolio. Fcom’s custom crystal engineering can adjust electrode geometry and cut angle to hit non-standard CL. Your part won’t be limited to what’s in the catalog.
Request a custom crystal

Your ESR requirement is tighter than standard.

Your IC’s oscillator stage is weak, or your frequency and package combination drives ESR higher than the IC can tolerate. Our engineering team can review your oscillator circuit design and suggest alternative matching approaches — different crystal modes, adjusted external components, or a packaged oscillator instead of a bare crystal.
Talk to an engineer

It matches on paper. But reality is not like that.

Start-up fails at low temperature. Frequency is off after reflow. The oscillator runs for minutes, then stops. These are gain margin, drive level, or soldering-induced frequency shift problems — and they need someone looking at your schematic and layout, not a matching table. Upload your design files in Section 2.
Upload your files for review

Contact Us Anytime

Drag & Drop Files, Choose Files to Upload

Contact Us Anytime

Drag & Drop Files, Choose Files to Upload