How to Choose SMD Quartz Crystals for MCU and RTC Designs
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Selecting the right SMD quartz crystal is a critical step in achieving stable clock performance for both MCU clock crystal and RTC crystal 32.768kHz applications. Package size alone is not enough. Frequency range, crystal structure, ESR, and application type must be considered together to avoid startup failures or long-term drift.
This guide explains how to approach SMD quartz crystal selection based on real design requirements, using three Suntan standard products as references: Suntan TSQ-3225SMD, Suntan TSQ-2016SMD, and Suntan TSQ-3215SMD.
MCU Clock Crystal Selection (High-Frequency Designs)
MCU and SoC designs typically require crystal frequencies in the MHz range to drive system clocks, communication timing, or peripheral control. For these applications, AT-cut fundamental-mode crystals are commonly used.
Key Selection Factors for MCU Designs
- Operating frequency range
- Equivalent Series Resistance (ESR)
- Package size and PCB layout constraints
- Compatibility with reflow soldering
Suntan TSQ-3225SMD
Suntan TSQ-3225SMD is designed for high-frequency MCU clock applications where electrical margin and layout stability are priorities.
- Package size: 3.2 × 2.5 mm
- Frequency range: 12 MHz to 54 MHz
- AT-cut, fundamental mode
- Designed for automatic mounting and reflow soldering
Commonly selected for industrial controllers, communication modules, and general-purpose MCU designs where ESR margin and stable oscillation are required.
Suntan TSQ-2016SMD
Suntan TSQ-2016SMD targets space-constrained MCU designs while maintaining high-frequency capability.
- Package size: 2.0 × 1.6 mm
- Frequency range: 20 MHz to 54 MHz
- AT-cut, series or parallel resonance
- Low aging with shock and vibration resistance
Commonly used in compact embedded systems and wireless modules where PCB area is limited. Validate oscillator startup margin based on your design constraints.
RTC Crystal 32.768kHz Selection (Low-Power Timekeeping)
RTC circuits operate differently from MCU clocks. They rely on 32.768 kHz tuning-fork crystals optimized for ultra-low power consumption and long-term frequency stability.
Suntan TSQ-3215SMD
Suntan TSQ-3215SMD is a dedicated RTC crystal and should not be treated as a general-purpose clock source.
- Package size: 3.2 × 1.5 mm
- Fixed frequency: 32.768 kHz
- Tuning fork crystal structure
- Designed for reflow soldering (260℃ max)
Designed for real-time clocks, standby timers, and battery-powered systems requiring minimal current consumption.
MCU vs RTC Crystal Selection Summary
- MCU clock designs use MHz-range AT-cut crystals
- RTC designs use 32.768 kHz tuning-fork crystals for low-power timekeeping
- Do not interchange MCU and RTC crystals due to fundamentally different operating requirements
Video Reference: Visual Package and Application Overview
This video provides a visual comparison of SMD quartz crystal packages and typical use cases for MCU and RTC designs.
Prefer to open in YouTube: https://youtu.be/u4rc26Fn6Kk
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