Traditionally, RTCs have used an external crystal for timekeeping, and over long periods of time, some crystal-based solutions can accumulate significant errors. The 50/60 Hz AC power ubiquitous to the U.S. and Europe is a new and even more efficient method of providing RTCs with a clock source. By using the AC power line for timekeeping, designers can build devices that ultimately perform more accurately and reliably over the long term and better withstand extreme temperature changes.
Other features of Intersil’s new AC-driven RTCs include an automatic crystal oscillator backup in case the AC line frequency is lost (ISL12032); an integrated trickle charger that allows a rechargeable energy source such as a super capacitor or rechargeable battery to be used as a backup supply; dual alarms for reporting problems with system performance; a power status “brownout” alarm that allows the system to save vital information to memory before a complete power loss occurs; time stamp, which records the time and date of events including power loss, recovery, and tampering, a feature particularly important in metering devices; and a battery status monitor that provides warning if battery voltage drops below a certain threshold.
