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Real-time clock extends standby time of handhelds

Posted: 16 Jun 2008 ?? ?Print Version ?Bookmark and Share

Keywords:real-time clock? RTC chips? SPI bus interface?

NXP Semiconductors claims 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 100nA (0.15?W) on a 1.5V power supply, the real-time clock comes in a tiny 3mm x 3mm x 1mm package, making it suitable 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 portable electronics products; meanwhile, the device's 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. "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 real-time clock that can save 50 percent or more power."

Features of the PCF2123 RTC 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 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 6.25Mbit/s.

Accuracy on the real-time clock is maintained by using a quartz reference. Each of these CMOS-based, RTC/calendars uses a low-power 32.768kHz 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 standby devices, and in metering units.

The PCF2123 is a CMOS RTC and calendar optimized for low power consumption. It functions as the time manager accurately keeping time, controlling the periodic wake-up of the MCU core from hibernation mode, and providing a watchdog function to independently monitor MCU tasks. With power consumption at less than 0.15?W the RTC can be powered by a very small battery cell or a small super-cap. Housed in tiny 3mm x 3mm x 1mm leadless package, the RTC fits nearly anywhere minimizing the space needed to host this important timing and measurement function.

Samples of the PCF2123 real-time clocks are available now. Volume shipping begins in Q2 08.

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