Why Crystal Oscillator is 32.768Khz | Xtalong
Among the frequency components, 32.768kHz is the most eye-catching frequency point with the most abundant product line. All electronic devices equipped with time functions will use 32.768kHz crystal oscillators, and 32.768kHz real-time clock modules (RTC modules) are used as time references. Applied in daily life.
32.768kHz resonator
The 32.768kHz quartz resonator (quartz crystal) is the most commonly used basic frequency component (Tuning Fork Quartz Crystal), and watches, mobile phones, computers, outdoor LED displays, and clocks displayed on billboards in daily life are evolved from it . 32768Hz is a very important standard frequency, because 32768 is equal to the 15th power of 2, and 32768Hz can be divided by 15 times to obtain a time signal of 1 second.
The 32.768kHz resonator is mainly used in real-time clock applications and is also the signal source for the low-speed external clock (LSE) of the MCU. The typical parameters of 32.768kHz quartz crystal commonly used in MCU clock source are as follows:
Frequency: 32.768kHz
Frequency deviation: ±20.00ppm (@25°C ±5°C)
Aging: ±5ppm max (@25°C±3°C/year)
Inflection point temperature: 25°C ±5°C
Frequency Stability: (0.036ppm±10%)/°C2
Load capacitance (CL): 6.0pF to 12.5pF
Shunt capacitance (C0): 1.4pF typ
Drive level: 0.1μW typ, 0.3μW max
Operating temperature: -40 to 85°C
It should be noted that when an external crystal is used as the clock source, if the input and output of adjacent pins of the MCU are high-frequency pulses, it will interfere with the 32.768kHz signal and cause jitter, which will affect the timing and cause timing deviation. Therefore, the adjacent pin of the external crystal oscillator should not be used as the input and output port of the high-frequency signal.
32.768kHz oscillator
32.768kHz crystal oscillators (crystal oscillators) are precision frequency devices, which are assembled from a 32.768kHz crystal and a CMOS oscillating circuit. Therefore, there is no need to connect any additional components when using it. Typical applications include general-purpose clock generators for digital systems, clock drivers for RTCs, clock retention for network servers and computers, mobile phones, field communication equipment, and water, electricity, and three-meter applications.
The typical performance and requirements of commonly used 32.768kHz oscillators are as follows:
Ultra-low power consumption: generally no more than 300nA
Wide Input Voltage: 1.2V to 5.5V
Working temperature: -10°C to +85°C
Narrow frequency difference: ±20ppm
Good output synchronization performance
Excellent oscillation stability: 0.2ppm/V
lower aging decay
Can withstand moving shock and vibration
RTC module
The RTC module is a product that integrates a 32.768kHz crystal oscillator and a real-time clock chip. It has an oscillation circuit, clock function, calendar function and alarm function. In order to obtain a more accurate time, the module should use a high-precision frequency oscillator (quartz wafer) and a chip for controlling components, and pay attention to the best match between the crystal oscillator and the RTC chip.
The RTC module is oriented to specific applications, requiring high precision, high stability, and low power consumption. It supports the I2C bus and provides functions such as calendar information, alarm clock, and timer. Due to the poor temperature characteristics of ordinary tuning fork crystals (Tuning Fork Quartz Crystal), some RTC modules for financial, electric power, communication and other applications use TCXO to improve frequency accuracy. For example, the characteristic parameters of Epson RX-4803LC are as follows:
Built-in 32.768kHz temperature compensated oscillator (digital TCXO) wave source
Frequency accuracy: (±3.4×10-6 at -40 to +85°C, ±5×10-6 at -40 to +85°C)
1/100-Second Timer Control Register
Interface voltage range: 1.6V-5.5V
Temperature compensated operating voltage range: 2.2V-5.5V
Timing (hold) voltage range: 1.6V-5.5V
Clock output with selectable frequency (32.768kHz, 1024Hz, 1Hz)
Clock, calendar function, alarm function, timing function, built-in EVIN input function
Can be used as an oscillator (32.768kHz digital TCXO) by connecting the terminals
The RTC module provides a high-performance and simple solution for building a high-precision synchronous time processing system. The main applications include various clocks and watches, financial systems, power meters, security systems, and road toll systems. Since there is no need to adjust the frequency, the user's design efficiency, product quality and time to market are improved.