Real-Time Clock

A real-time clock (RTC) is a specialized integrated circuit used in data logging modules and other industrial electronic systems to maintain accurate timekeeping even when the main system power is off. It enables timestamped data recording for process monitoring, compliance documentation, and event sequencing. The RTC operates from a quartz crystal oscillator that generates precise timing signals, and it uses a backup battery or capacitor to sustain timekeeping during power interruptions. The clock circuit counts oscillations to track seconds, minutes, hours, and date, providing synchronized time data to the logging system.

This directory entry covers RTC components intended for integration into electronic assemblies. The listed parameters are typical reference ranges and must be verified for the specific model and application. For example, timekeeping accuracy is typically ±2 ppm at 25°C for temperature-compensated modules, but actual performance depends on the crystal and circuit design. Supply voltage ranges from 1.8 V to 5.5 V to accommodate 3.3 V and 5 V systems. Timekeeping current is typically 0.3–1.0 µA at 3.3 V, and battery backup current is 0.3–0.8 µA at 3.0 V. The minimum timekeeping voltage with battery backup is 1.3–5.5 V. The oscillator frequency is 32.768 kHz, a standard watch crystal frequency. Interfaces include I2C and SPI, selected based on microcontroller peripheral availability. Operating temperature range is –40 to 85 °C (industrial grade), with extended ranges available on request. Package types include SOIC-8, MSOP-8, and DFN-8. ESD tolerance is 2000 V (Human Body Model) per IEC 61340-3-1, ensuring robustness in handling. Humidity range is 5–95% RH non-condensing.

When selecting an RTC, verify the supply voltage, interface compatibility, and backup battery requirements. Confirm the timekeeping accuracy and temperature range for your environment. Check the ESD tolerance and package footprint for assembly. Always consult the legal manufacturer or supplier for model-specific values and standards compliance.

The RTC uses a quartz crystal oscillator to generate a stable 32.768 kHz signal. The crystal's piezoelectric properties produce precise electrical oscillations when voltage is applied. The clock circuit divides this frequency to count seconds, minutes, hours, and date. A backup battery or capacitor maintains power to the oscillator and counting circuitry during main power loss, ensuring continuous timekeeping. The RTC communicates time data to the host system via I2C or SPI interfaces, allowing synchronized timestamping.