Real-time clock (RTC) ICs

Real-time clock (RTC) ICs with parallel or serial interface, including ultra-low-power devices

ST offers a wide portfolio of real-time clock (RTC) ICs with parallel or serial interface, including ultra-low-power devices packaged in standard SMD SOX18 and SOX28 with embedded ±5ppm 32kHz factory-calibrated Crystal.

Our devices offer many value-added features such as supervisory functions that include alarm, battery switchover, and reset as well as special features with time stamp and anti-tamper for secure applications.


Real-time clock (RTC) ICs can be used on a broad range of applications.

Product types

SNAPHAT with Battery & Crystal for SOH packages
These devices are detachable lithium power sources with embedded 32-kHz crystal housed in a special top called SNAPHAT®. They are compatible with ST’s Serial RTC and nonvolatile TIMEKEEPER® surface-mount in SOIC (MH) package.
ST's parallel real-time clock ICs, also called Timekeepers, combine a SRAM with up to 256 Kbytes of memory and a byte-wide interface along with a quartz-based very-low-power oscillator with a clock/calendar circuit to provide real-time data.
Advanced RTC ICs include additional features such as programmable alarms, watchdog timers, system reset outputs and battery-low warning flags.
SOX18 Embedded Crystal (internal View)
ST's serial real-time clocks range from ultra-low power devices for portable applications to high-accuracy parts with analog calibration up to factory-calibrated RTC modules with an embedded crystal.


Along with ST’s serial and parallel RTC portfolio, ST's unique SNAPHAT® devices have a special removable/replaceable top that contains a lithium coin-cell battery and a 32-kHz crystal designed to be "snapped on" after the surface mount process. It solves the reflow compatibility of the lithium batteries and provides a solution compatible with all ST's real-time clocks in surface-mount SOH-28 and SOH-44 packages.

All ST RTCs are Underwriters Laboratories® (UL) recognized, see application note AN1011; "Battery technology used in NVRAM and real-time clock (RTC) products".

Home and Professional Appliances:
  • Integrated switchover
  • Long time retention with capacitor backup
  • Embedded crystal
  • Low standby current
  • Analog and digital calibration
Bridge and Gateway:
  • Analog and digital calibration
  • Embedded crystal with factory calibration
  • NVRAM for retention of configuration data
  • Tamper detection
  • Replaceable battery and crystal

Real-time clock (RTC) design support

To make designing with real-time clock ICs even easier, ST offers two simulators:

See also our summary of development hints in application note AN3060;"Application guide for serial real-time clocks (RTCs)".