Quartz Crystal Oscillator HC‑49S Series – Support Documentation
Overview
This page covers the full family of HC-49S through-hole quartz crystal parts. These are passive resonators used with an external oscillator circuit (typically the Pierce oscillator built into most microcontrollers). They provide precise frequency references for microcontrollers, communications, audio, video, and timing systems.
Key Features
- Frequency range: approx. 3 MHz to 64 MHz in fundamental mode (other values possible).
- Common load capacitances (CL): 12 pF and 20 pF (18 pF also seen). Choose to match your oscillator circuit.
- Typical tolerance at 25 degC: +/-10 ppm to +/-30 ppm (tighter grades available).
- Typical stability over temperature: +/-10 ppm to +/-50 ppm (grade dependent).
- Drive level: keep low (order of tens to hundreds of microwatts) to minimise ageing and jitter.
- Ageing: typically within a few ppm in the first year.
- Package: metal can, through-hole, low-profile HC-49S.
Mechanical (typical)
- Body size: about 11.5 mm long x 4.7 mm wide x 3.5 mm high.
- Lead pitch: about 4.88 mm, lead diameter about 0.45 mm.
- No polarity; either lead may go to XIN or XOUT.
Electrical Integration (Pierce oscillator basics)
Most MCUs use a Pierce oscillator. Connect the crystal between XIN and XOUT. Fit two load capacitors (C1 from XIN to ground, C2 from XOUT to ground). Choose C1 and C2 so their series combination plus stray capacitance equals the crystal CL.
Rule of thumb starting values:
- For CL 20 pF, start with C1 = C2 about 27 pF (assumes a few pF stray per node).
- For CL 12 pF, start with C1 = C2 about 15 pF to 18 pF.
Layout tips: keep the loop (XIN, crystal, XOUT, load caps) short and symmetrical, avoid vias, and keep noisy signals away. Do not run a ground or power plane directly under the loop if it increases stray capacitance.
Series Values (includes your listed parts and future-proof extras)
All frequencies below are available in the HC-49S outline. The values you list on the website are included. Units are MHz unless noted.
| Frequency | Typical CL | Common uses / notes |
|---|---|---|
| 4 | 20 pF | Basic MCU clocks |
| 6 | 20 pF | Legacy USB LS/FS derivations, general logic |
| 7.3728 | 20 pF | UART-friendly divisors |
| 8 | 20 pF | MCUs, RF front-ends |
| 10 | 20 pF | Reference clocks, instrumentation |
| 11.0592 | 20 pF | UART base for 115200 bps (x16) |
| 12 | 20 pF | MCUs, FS-USB PLL bases |
| 12.288 | 20 pF | Audio 256 x 48 kHz |
| 14.7456 | 18–20 pF | Video/serial timing |
| 16 | 18–20 pF | Very common MCU clock (e.g. AVR) |
| 20 | 18 pF | Higher speed MCU, logic |
| 22.1184 | 18 pF | UART and audio multiples |
| 24 | 18 pF | USB/SDIO references |
| 24.576 | 12–18 pF | Audio 512 x 48 kHz |
| 25 | 12–18 pF | Ethernet PHYs, RF |
| 27 | 12–18 pF | RF/ISM references |
| 30 | 12 pF | High speed digital |
| 32 | 12 pF | MCUs, radios |
| 32.768 kHz | 12.5 pF | RTC watch crystal (note kHz unit) |
| 48 | 12 pF | USB and fast clocks |
| 50 | 12 pF | High speed reference |
| 64 | 12 pF | Upper end of common HC-49S range |
| 3.579545 | 20 pF | NTSC colourburst / legacy video |
| 3.6864 | 20 pF | UART-friendly |
| 9.216 | 20 pF | Audio 192 x 48 kHz |
| 18.432 | 18 pF | UART/audio multiples |
| 19.2 | 18 pF | Cellular/GNSS common reference |
| 26 | 12–18 pF | RF transceivers (ISM, LoRa, etc.) |
| 40 | 12 pF | MCU/FPGA PLL inputs |
| 49.152 | 12 pF | Audio 1024 x 48 kHz |
Selecting the right part
- Frequency: choose a value that divides exactly to your target rates (UART, audio, video, RF).
- CL: match the crystal load capacitance with your C1 and C2 choices; adjust a few pF if fine trimming is needed.
- Tolerance and stability: pick grades to suit the allowed ppm error over temperature.
- Drive: use the lowest reliable drive level to reduce ageing and jitter.
Troubleshooting
| Symptom | Likely cause | Fix |
|---|---|---|
| No oscillation or slow start | CL mismatch, long or asymmetrical traces, high stray capacitance | Recalculate C1/C2, shorten and balance traces, avoid planes under the loop |
| Frequency off by tens of ppm | Wrong CL network | Trim C1/C2 by 1–2 pF steps to pull frequency into range |
| Stops at temperature extremes | Insufficient stability grade or too much drive | Select tighter stability, reduce drive, keep away from hot parts |
| High jitter | Noisy supply or digital coupling into the loop | Improve decoupling, reroute away from fast edges and clocks |
FAQs
- Is there a polarity? No. Either lead can connect to XIN/XOUT.
- Can I use an SMT crystal instead? Yes, if frequency, CL, tolerance/stability and drive limits match.
- Why 11.0592, 14.7456, 22.1184 MHz? These give exact UART divisors and clean audio/video ratios.
- Is 32.768 kHz available in HC-49S? Yes. Note it is kHz and usually specified with CL about 12.5 pF.
Safety and Handling
- Handle with ESD care and avoid bending leads at the can interface.
- Keep soldering heat brief; allow to cool before power-up testing.
- Store dry to minimise ageing drift.