Q: How to select a crystal based on the MCU datasheet?

A: A “wide temperature” crystal refers to a crystal designed to maintain stable frequency performance across a broader operating temperature range than standard commercial products. In SJK’s product portfolio, different temperature grades are available according to application requirements.

Some SMD crystal series support operating temperatures from -20°C to +70°C, with -40°C to +85°C options available, while automotive-grade crystal products can support operating temperatures extending to -40°C to +125°C. These wider temperature ranges are suitable for applications exposed to demanding environmental conditions, including automotive and industrial electronics. SJK also offers crystal products with different frequency tolerances, load capacitances, and drive levels, allowing the specifications to be matched to different circuit requirements. When selecting a wide-temperature crystal, the required operating range should therefore be considered together with frequency stability and other electrical parameters to ensure proper compatibility with the target application.

A: SJK recommends several measures for reducing EMI in crystal and oscillator circuit designs, including shorter signal traces, a damping resistor, shielding, and lower voltage. These measures can be considered as part of the circuit design when addressing electromagnetic interference.

We also provide differential oscillators for high-speed digital applications, supporting industry-standard differential output formats including LVDS, LVPECL, HCSL, and CML. Our differential oscillators feature signal integrity, ultra-low phase jitter, and EMI performance. In addition, our oscillator portfolio includes SPXO, VCXO, TCXO, OCXO, MEMS, and other frequency-control products. When customers select an oscillator, we recommend considering the required frequency, output format, and electrical requirements together with the circuit design and layout to meet the application's frequency-control and EMI requirements.

A: An RTC crystal is a 32.768 kHz quartz crystal used as a frequency reference for real-time clock applications and timekeeping. At SJK, we provide 32.768 kHz crystal products in both traditional cylindrical and SMD packages. Our cylindrical tuning-fork crystals are available in 2×6 mm and 3×8 mm sizes, while our SMD versions include 1610, 2012, 3215, and 7015 packages. We offer load capacitance options of 6 pF, 7 pF, 9 pF, and 12.5 pF, with standard frequency tolerances of ±10 ppm and ±20 ppm.

Our 32.768 kHz crystals are designed for applications requiring low power consumption and stable frequency performance. We also provide RTC-related products, including low-power, temperature-compensated, AEC-Q200 automotive-grade, and ultra-compact SMD solutions for industrial, automotive, IoT, and low-power embedded systems. This product range allows us to support different RTC timing and packaging requirements.

A: We calculate the external capacitors using the formula C1 = C2 = 2 × (CL - Cs), where CL is the required load capacitance and Cs represents parasitic capacitance. The parasitic capacitance is typically 3–5 pF. When selecting external capacitors for a crystal oscillator circuit, we recommend considering the required load capacitance specified for the crystal together with the oscillator circuit requirements.

At SJK, we provide crystal units for different electronic designs, including MHz crystals and 32.768 kHz crystals, as well as SMD crystal resonators in multiple package sizes. Our product portfolio supports frequency-control requirements with a focus on high precision, miniaturization, and low power consumption. By matching the crystal's load capacitance with the circuit design and calculating the external capacitors accordingly, engineers can select a suitable configuration for their application.