Inside the PCA8525 and PCF8525: A Q&A on the World’s Most Advanced Temperature Compensated RTC ICs

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In this Q&A, we cover common topics surrounding the PCA8525 and PCF8525 high-accuracy real-time clock (RTC) integrated circuits (ICs). Delivering up to 5x better timekeeping accuracy than standard RTCs, ultra-low current draw, a compact printed circuit board (PCB) footprint, on-chip temperature sensing, and 32.768 kHz crystal supply flexibility, these products bring RTC-module-level performance to discrete designs.

Q: Every manufacturer seems to claim that their RTC is “accurate,” but the datasheet for the PCA8525 and PCF8525 reveals exceptional precision. What makes it 5× more accurate than a standard RTC IC?

A: It's simple—real, continuous, digital temperature compensation. The PCA8525 and the PCF8525 in the HVSON package are the first RTC ICs to implement their own internal temperature compensation engine, which corrects quartz drift across temperature. This built-in digital-compensation engine enables:

  • Up to 5x better accuracy than standard RTC ICs that lack any temperature compensation.
  • Typical accuracy of up to ±30 ppm across -40°C to +85°C for the PCF8525 and -40°C to +125°C for the PCA8525 with a standard 32.768 kHz tuning fork crystal.
Watch the video to see the next generation of RTC ICs in action.

Q: That's impressive, but what about power? Does the PCA8525 and PCF8525 draw a lot of current like most compensated RTCs?

A: Both the PCA8525 and PCF8525 provide temperature-compensated accuracy, while maintaining nanoamp-level timekeeping current. In timekeeping mode at 3.3 V, both devices offer exceptionally low power consumption:

  • PCF8525: Typical timekeeping current of 64 nA
  • PCA8525: Typical timekeeping current of 106 nA.

To put that in perspective, you get TCXO class accuracy at a current level comparable to the lowest power RTCs on the market. In real world applications, the PCF8525 can run on a CR2032 coin cell battery for 10+ years versus 1 month for others.

Q: Many designers are moving to miniature packages. How small does the PCF8525 run?

A: It's small enough to fit into tiny wearables and IoT nodes. The PCF8525 is available in a WLCSP12 package at 1.6 mm x 1.2 mm. By prioritizing this extreme footprint and omitting the temperature compensation hardware, we provide a solution for applications where space is the most constrained resource.

This application diagram, typical for the PCF8525 features crystal, power, and system connections.

Q: You mentioned an on-chip temperature output. Why include a digital temperature readout in an RTC?

A: For HVSON devices with the compensation engine active, this information is available to the system through an 8-bit temperature register with 1°C resolution. This offers free temperature readout without extra components for many battery-powered designs.

Q: RTC modules typically have an integrated quartz crystal but require 100% factory calibration to achieve high accuracy. This process takes a long time due to fine tune adjustments at multiple temperature points. You’re saying designers can choose any crystal vendor and still get module level accuracy? How?

A: This is perhaps the biggest breakthrough of the PCA8525 and PCF8525 in HVSON: full temperature compensation with a standard external crystal.

Unlike typical RTC ICs, which leave the crystal uncompensated, the PCA8525 and PCF8525:

  • Work with any 32.768 kHz tuning fork crystal at CL = 7 pF.
  • Digitally compensates frequency drift using the crystal’s temperature coefficient.
  • Provides aging offset registers to fine tune accuracy over long deployments.

This means designers get:

  • The flexibility of sourcing crystals from multiple vendors.
  • The accuracy is usually achievable only with pre-matched RTC + crystal modules
  • The cost advantage of not needing a custom TCXO or integrated module.

Q: Beyond accuracy, what additional features help engineers in real applications?

A: The PCA8525 and PCF8525 are packed with practical features, including battery switchover (timing preserved down to 0.9 V), timestamping for event logging or security tampers, dual alarms, and a programmable CLKOUT.

PCA8525/PCF8525 deliver precise timing for mission‑critical IoT and autonomous systems.

Summary: Why choose the PCA8525 or PCF8525?

  1. Better Accuracy: Up to 5x that of standard RTCs.
  2. Ultra Low Power: Just ~64 nA for the PCF8525 and ~106 nA for the PCA8525, perfect for applications that require extended battery life operation.
  3. Crystal Supply Flexibility: Freedom to select from a multitude of crystal suppliers without sacrificing performance.
  4. Smaller Designs: The tiny WLCSP footprint for densely packed PCBs.
  5. Added Value Functions: Includes alarms, watchdog, and battery switchover across the family.

The PCA8525 and PCF8525 create a new category of RTC ICs that deliver module class accuracy and ultra-low power consumption with two package options.

Author

Robert Gee

Robert Gee

Product Marketing Director of General Purpose and High Speed Interface Products at NXP Semiconductors

He has more than 30 years of technical marketing experience in multi-market applications and electronic distributor business. He is currently focused on general purpose I/O expanders, voltage level translators, high speed interface, and legacy analog devices. He graduated with a BSEE from University of Massachusetts at Amherst and currently lives in Sunnyvale California.