Real-time clocks offer accuracy, low power dissipation

Intersil Corp. recently introduced the ISL1218 and ISL1220 micropower real-time clock/calendar (RTC) devices. With on-chip timing and crystal compensation, the two devices promise accurate timekeeping with very low power dissipation, the company said.

The accuracy of an RTC typically depends on the frequency of the external crystal used as the time basis. However, Intersil said its new RTCs allow designers to adjust integrated analog and digital timing registers to trim the internal oscillator for initial accuracy. The devices also feature power failure detection, periodic or polled alarm, intelligent battery backup switching, 8bytes of battery backed SRAM and the company's InterSeal battery-saving technology to prevent initial battery drain prior to first use.

The ISL1220 has a separate FOUT pin to allow clocking of the micro through RTC while having a separate alarm pin. The ISL1218 is housed in an 8-lead SOIC or MSOP package, and the ISL1220 is housed in a 10-lead MSOP package. Small packaging and integrated functionality save designers cost and board space.

The alarm can be set to any clock/calendar value for a match (for example: every minute, every Tuesday or at 5:23 AM on March 21). The alarm status is available by checking the Status Register, or the device can be configured to provide a hardware interrupt via the IRQ pin. There is a repeat mode for the alarm allowing a periodic interrupt every minute, every hour, every day, etc.

These devices target industrial applications, including power meters, control units, security systems, ATMs, cameras, vending machines and electronic door openers; medical applications, including portable medical instruments, defibrillators and glucose meters; and handheld units, such as point-of-sale terminals and scanners.

The ISL1218 and ISL1220 are available today with prices starting at $1.27 and $1.14 each, respectively, in 1,000-unit quantities. Intersil also provides evaluation boards for the new I?C RTC family.