RTC 27 Click— MikroE's 2,000th Click board™—features NXP's PCF8525 real-time clock (RTC). NXP and MikroE celebrate a significant milestone in our long-standing partnership, helping developers more easily evaluate and accelerate innovation with analog and mixed-signal solutions.
In a recent blog post , MikroE highlighted the RTC 27 Click—its 2000th Click board release. Featuring NXP's new PCF8525 RTC, the board marks an important milestone in our long-standing collaboration. Recently announced, the PCF8525 is a Real-Time Clock Integrated Circuit (IC) that includes a temperature sensor for increased timekeeping accuracy enabling the creation of easy to use, intuitive ecosystems for evaluating NXP's analog and mixed-signal solutions. This blog shares why this development is significant.
Introducing the First Real-Time Clock IC with Temperature Compensation
When it comes to timekeeping solutions, RTCs are the standard. Usually, an RTC includes Hour:Minute:Second and Day:Weekday:Month:Year structures to track time and date. RTCs may also include alarms, timers, watchdog timers and other features to handle event generation and tracking.
Typically, there are two flavors of devices: RTC ICs and RTC modules. The difference between the types is simple, but significant. ICs require an external crystal or microelectromechanical systems (MEMS) oscillator to provide a 32.768 kHz clock, used as the time base of the system. On the other hand, RTC modules implement a crystal or MEMS oscillator directly on the packaging along with the IC itself, creating a one-component solution with a number of advantages, mainly, high accuracy due to factory calibration.
However, there is a tradeoff that comes with choosing between RTC ICs and RTC modules. As accuracy increases with RTC modules, so does cost, which is impractical for cost-constrained applications. On the other hand, while simpler devices can be more cost effective, the need for an external oscillator affects accuracy.
This has been an ongoing debate when selecting IC + Crystal versus a more streamlined module. But what if there was a middle ground?
The PCF8525 provides a solution in a clever and intuitive way as the RTC IC that integrates a temperature-compensation engine.
The combination of a temperature-compensation engine, aging- and offset-calibration registers and on-chip load capacitors help designers optimize oscillator performance. Together, these capabilities can improve the accuracy of an RTC IC and crystal solution by up to five times. The accuracy is not only obtained at room temperature—condition most accuracy and drift calculations assume as true—but it is maintained across the entire -40 °C to +85 °C temperature range.
This is critical for applications exposed to temperature fluctuations as it ensures consistent, predictable drift that can be easily corrected by using the provided registers, further enhanced by software running correction algorithms.
This PCF8525 application diagram features its crystal, power and system connections. For a better experience, download the PCF8525 application diagram.
Understanding Real-Time Clock Drift and Accuracy
32.768 kHz crystals are typically fabricated to a ±20 ppm drift at room temperature. However, when taken outside this ideal temperature, crystal behavior tends to drift significantly upwards of ±200 ppm at higher temperatures. This happens because quartz crystal accuracy is based on a quadratic model where accuracy drift scales with the square of temperature, therefore creating significant drift with slight changes to ambient temperature. This makes it extremely hard to maintain accuracy in devices that are exposed to very high or very low temperatures, or those who are exposed to quick changes of environment.
The difference is significant—±100 ppm of drift represents an inaccuracy of 52 minutes per year, with ±10 ppm having only 5.2 minutes in the same period. Accumulation of those inaccuracies across a long application lifetime is significant, especially where always-on requirements exist which are typical in industrial, factory, medical and automotive applications.
This is where PCF8525 shows its capabilities versus other solutions. Specifically, the integrated temperature compensation engine performs real-time correction of the accuracy drift curve based on the on-chip ±4 °C-accurate temperature sensor. Such combination opens the door to a previously untapped realm of performance and accuracy. This positions the PCF8525 (±30 ppm) in between ultra-high accuracy RTC Modules, (such as the PCF2131 with± 3 ppm) and standard accuracy, uncompensated RTC ICs (such as the PCF85063 at >50 ppm).
The Benefits of Ultra-Low Power of (ULP) Operation
Add ICs to its high accuracy, the PCF8525 is also an ULP device, with a typical 100 nA current consumption, even when utilizing the full power of the temperature compensation engine.
For battery powered applications, the device also contains a configurable battery switchover circuit with direct and indirect operation modes. This is useful with cases where supply and battery voltages differ or need special consideration for switching or facilitating integration.
The PCF8525 is also available as an automotive-qualified IC for high-reliability automotive always-on applications that require ULP and High-NG accuracy timekeeping.
Addition of this family to the portfolio further expands NXP's timing portfolio, giving designers more options to tailor performance, power consumption and solution costs of their application requirements.
