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New PCF2123 Real Time Clock Sets New Record in Power Efficiency

This new RTC features a tiny foot print with extremely long stand-by time,

NXP, has launched one of the industry's best low-power performance real-time clock (RTC) chips with SPI bus interface, the PCF2123. Operating at a current of less than 100 NanoAmperes (0.15µW) on a 1.5-V power supply, the real-time clock comes in a tiny 3x3x1mm package, making it ideal for battery operation and handheld applications to keep track of time, when the equipment is powered down. The small size and low-power requirement of the PCF2123 make it a good choice for applications including home-use medical devices such as blood pressure monitors, portable phones, PDAs and similar compact portable electronics products where space and power are critical, while the variety of features makes it suitable for industrial systems as well as white goods.

“Power consumption is probably the most important feature of RTCs, directly correlated to the battery life of the electronic equipment,” said Markus Hintermann, international product manager, interface product line, NXP Semiconductors. “Three parameters are very critically watched during system design including accuracy, power consumption and size. Using precision engineering, NXP has been able to develop a groundbreaking real-time clock that can save 50 percent or more power.”

Features of the PCF2123 real-time-clock include a freely programmable alarm and timer function that gives designers the option to generate a wake-up signal on an interrupt pin. A programmable offset register also allows fine-tuning of the clock and frequency adjustment. The seconds, minutes, hours, days, weekdays, months and years registers are all coded in binary-coded decimal (BCD) format for easy conversion to decimal digits for printing or display and faster decimal calculations. Data is transferred serially via an SPI bus with a maximum data rate of 6.25 Mbits per second.

Accuracy on the real-time clock is maintained by using a quartz reference. Each of these CMOS-based, real-time clock/calendars uses a low-power 32.768-kHz quartz oscillator to provide clock and calendar functions. The calendar functions track year, month, date, and day with built-in century and leap-year flags. The tolerance of the quartz and the physical environment around the quartz crystal and oscillator circuit can be easily calibrated via the on-chip calibration register. No other external parts are required.

Real-time clocks are indispensable for time keeping, process control and other time-critical tasks found in time-keeping applications, battery-powered stand-by devices, and in metering units. The PCF2123 is a CMOS real-time clock and calendar optimized for low power consumption. It functions as the time manager accurately keeping time, controlling the periodic wake-up of the microcontroller core from hibernation mode, and providing a watchdog function to independently monitor microcontroller tasks. With power consumption at less than 0.15uW the RTC can be powered by a very small battery cell or a small super-cap. Housed in tiny 3x3x1mm leadless package, the RTC fits nearly anywhere minimizing the space needed to host this important timing and measurement function.

Features of the PCF2123 SPI Real-time Clock/Calendar

  • Real time clock provides year, month, day, weekday, hours, minutes, and seconds based on a 32.768 kHz quartz crystal
  • Low backup current while running: typical 100 nA at VDD = 2.0 V and Tamb = 25 °C
  • Resolution: seconds to years
  • Watchdog functionality
  • Freely programmable timer and alarm with interrupt capability
  • Clock operating voltage: 1.1 V to 5.5 V
  • 3 line SPI-bus with separate, but combinable data input and output
  • Serial interface at VDD = 1.8 V to 5.5 V
  • 1 second or 1 minute interrupt output
  • Integrated oscillator load capacitors for CL = 7 pF
  • Internal Power-On Reset
  • Open-drain interrupt and clock output pins
  • Programmable offset register for frequency adjustment

More information on the PCF2123 SPI Real-time Clock/Calendar, can be found on the NXP website at NXP PCF2123 product page

The NXP website address is www.nxp.com
[Reprinted with kind permission from NXP]