Real Time Clocks (RTC) Analog Devices Inc. Real-time Clocks (RTCs) are offered in a wide range of low-power, highly accurate, small packages, and MEMs-based ICs. RTC ICs measure time, even when the power of the main device is off, so an auxiliary battery or supercapacitor are required. Power consumption is a key factor in most RTC designs, but accuracy and small package size are also important. The latest RTC ICs reduce package pin count by supporting a serial interface.