Intersil's Real-Time Clocks can use lower-cost crystals

18th September 2006

ES Admin

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Intersil has introduced two micropower real-time clock/calendar devices. The ISL1218 and ISL1220 with on-chip timing and crystal compensation deliver accurate timekeeping with very low power dissipation. The introduction of the devices means that using a lower-cost, 32.768kHz quartz crystal is now a practical and accurate option.

The accuracy of an RTC typically depends on the frequency of the external crystal that is used as the time basis. However, the ISL1218/20 allow designers to adjust integrated analogue and digital timing registers to trim the internal oscillator for initial accuracy.

The designer can adjust the on-chip oscillator through an I2C digital interface. The analogue trimming register calibrates on-chip digital capacitors and the digital timing register adjusts the timing counter.

The ISL1218/20 also feature power failure detection, periodic or polled alarm, intelligent battery backup switching, 8 bytes of battery backed SRAM (static random access memory) and Intersil’s battery-saving InterSeal 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 combine to save designers cost and board space.

Intersil’s InterSeal Battery Saver prevents initial battery current drain before the devices are first used. For example, battery-backed RTCs are commonly packaged on a board with a battery connected. In order to preserve battery life, these devices will not draw any power from the battery source until after the device is first powered up from the VDD source.

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.

Other key features include 15 selectable frequency outputs, single event or pulse interrupt mode, 400kHz data transfer rate, 400nA battery supply current, same pin out as ST M41Txx and Maxim DS13xx devices, and Pb-free plus anneal availability (RoHS compliant).

Target applications include Industrial, embracing power meters, control units, security systems, ATMs, cameras, vending machines and electronic door openers, medical, including portable medical instruments, defibrillators and glucose meters, and handheld units, such as point-of-sale terminals and scanners.

The ISL1218 is available now in 8-lead SOIC and MSOP packages, and the ISL1220 is offered in a 10-lead MSOP. Intersil also provides evaluation boards for the new I2C real-time clock family.