How to Choose SMD Quartz Crystals for MCU and RTC Designs

January 21, 2026 | tags SMD quartz crystal selection MCU clock crystal RTC crystal 32.768kHz SMD quartz crystal quartz crystal selection guide MCU crystal oscillator RTC tuning fork crystal 32.768kHz crystal SMD AT-cut quartz crystal SMD crystal package comparison 2016 SMD crystal 3215 SMD crystal 3225 SMD crystal low power RTC crystal MCU clock design crystal | views

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SMD quartz crystal selection for MCU clock crystal and RTC crystal 32.768kHz designs

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

MCU clock crystal · 12–54MHz class

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.

View TSQ-3225SMD Product Page

MCU clock crystal · compact footprint

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.

View TSQ-2016SMD Product Page

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.

RTC crystal 32.768kHz · tuning fork

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.

View TSQ-3215SMD Product Page

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