Most real time clocks are based on 32.768 kHz quartz crystals of tuning fork type. These crystals have a parabolic frequency/temperature characteristic and the accuracy can vary as much as ±30 ppm over the device’s operating conditions. Therefore, in applications that use an RTC with external crystal, the accuracy of the time-keeping function can vary significantly. To compensate for this, an external temperature sensor can be used to adjust for any temperature-dependent drifts. However, with NXP’s accurate RTCs, the user can eliminate the use of these several external components and still achieve a nominal accuracy of ±3 ppm.