TF-CR-3225-8MHz

The load capacitance (CL) is the effective capacitance seen by the crystal in the oscillator circuit. It is calculated as CL = (C1 × C2) / (C1 + C2) + Cstray, where C1 and C2 are the external load capacitors and Cstray is the stray capacitance of the PCB and IC pins (typically 3-7pF). For a crystal specifying 20pF load capacitance, and assuming 5pF stray capacitance, you would calculate: 20pF = (C × C) / (C + C) + 5pF, which gives C = 30pF for each capacitor. In practice, use standard values like 22pF or 33pF and measure the actual oscillation frequency. Adjust the capacitor values if the frequency is off. Using load capacitors that are too large increases power consumption and may prevent oscillation. Using values that are too small results in frequency higher than specified and may affect stability.

Use the formula CL = (C1 × C2) / (C1 + C2) + Cstray to calculate load capacitors. Start with standard values and adjust based on frequency measurement.

A crystal (quartz crystal resonator) is a passive component that provides frequency reference when used with an external oscillator circuit (typically inside a microcontroller or separate IC). The crystal requires external circuitry to oscillate. An oscillator (crystal oscillator or XO) is a complete active module containing the crystal, oscillator circuit, and buffer in a single package. It provides a clock output directly without external components. Crystals are lower cost and lower power but require external circuitry. Oscillators are easier to use (just connect power and get clock output) but are more expensive and consume more power. Choose crystals for cost-sensitive designs with available oscillator circuitry. Choose oscillators for simplicity, guaranteed startup, or when the IC lacks internal oscillator circuitry.

Choose crystals for cost-sensitive designs with microcontroller internal oscillators. Choose oscillators for guaranteed startup and simplified design.

Frequency tolerance is the maximum deviation from the nominal frequency at a specific temperature, typically 25C. For example, ±30ppm tolerance at 25C means the actual frequency will be within ±30 parts per million of 8MHz (±240Hz) at room temperature. Frequency stability is the maximum deviation over the operating temperature range. For example, ±50ppm stability from -20C to +70C means the frequency may shift by up to ±50ppm (±400Hz for 8MHz) as temperature changes. These specifications are important for applications requiring precise timing. For UART communication at 115200 baud, ±1% accuracy is typically sufficient. For USB, ±0.25% (2500ppm) is required. For precision timing or high-speed communication, tighter tolerances may be needed.

Select frequency tolerance based on your application's timing accuracy requirements. Contact us for recommendations on crystal specifications for specific communication protocols.

Using a crystal with different load capacitance than specified will cause the oscillation frequency to shift. If the actual load capacitance is higher than specified, the frequency will be lower. If the actual load capacitance is lower, the frequency will be higher. The relationship is approximately: Δf/f ≈ -0.5 × (CLactual - CLspecified) / CLspecified. For example, using 30pF load instead of 20pF specified would shift the frequency down by approximately 0.25% or 2500ppm. This may be acceptable for some applications but could cause timing issues for communication protocols. It's best to use the specified load capacitance. If you must use a different value, measure the actual oscillation frequency and verify it meets your application requirements. Some applications can tolerate frequency shifts better than others.

Always use the specified load capacitance for best accuracy. If different values must be used, measure and verify the actual oscillation frequency.

Drive level is the power dissipated in the crystal during oscillation, typically specified in microwatts (uW). The TF-CR-3225-8MHz has a maximum drive level of 100uW. Exceeding the maximum drive level can cause: Frequency shift due to crystal heating. Accelerated aging and reduced lifetime. In extreme cases, crystal damage or fracture. Insufficient drive level can result in: Failure to start oscillating. Unreliable startup, especially at temperature extremes. High phase noise or jitter. The actual drive level depends on the oscillator circuit design and supply voltage. Most microcontroller internal oscillators provide appropriate drive levels. For discrete oscillator designs, calculate or measure the drive level to ensure it's within the crystal's specifications. If the drive level is too high, add a series resistor to limit current.

Ensure the oscillator circuit provides drive level within the crystal's specified range. Contact us for drive level measurement and circuit design assistance.

Fundamental mode crystals oscillate at their fundamental resonant frequency, which is the frequency marked on the crystal. Overtone crystals are designed to operate at a harmonic (multiple) of the fundamental frequency. For example, a 24MHz overtone crystal might have a fundamental frequency of 8MHz but is designed to operate at the 3rd overtone (24MHz). Fundamental mode crystals are used for frequencies typically below 30-50MHz. Overtone crystals are used for higher frequencies where fundamental mode crystals would be too thin and fragile. The oscillator circuit must be designed for the specific mode - fundamental mode circuits won't work with overtone crystals and vice versa. Most common microcontroller crystals are fundamental mode. Overtone crystals are typically used for RF and high-frequency applications. The TF-CR series are fundamental mode crystals suitable for most microcontroller applications.

Use fundamental mode crystals for frequencies below 30MHz. Use overtone crystals for higher frequencies with appropriate oscillator circuit design.