Hi,
We are developing a custom PCB which contains the nRF52840 MCU as the main MCU on the PCB.
The PCB is battery powered and would need to support timekeeping even after the main batteries are missing.
For this we would add smaller backup batteries on the PCB which would power the external RTC while the main batteries are missing.
Our MCU would communicate with the RTC over I2C.
We are currently looking for the RTC component which would fit our use case and decided to ask for your support.
Because of the battery capacity constraints we would the external RTC to consume an average below 2-3 µA.
For the RTC we are looking for at least time resolution in seconds while any higher resolution (hundreds of seconds, miliseconds, ...) would be more optimal.
This RTC would also need save the timestamp in resolution in seconds of when the main batteries are taken out and the RTC powering source switches to backup batteries.
This timestamp is commonly referred to in RTC datasheets as Power-Fail Timestamp.
Also because we are developing on nRF52840 with Zephyr RTOS it would be beneficial if the RTC has driver support available in Zephyr or at least a C driver solutuion.
Requirements for the external RTC:
- Support for I2C slave interface compatible to communicate with nRF52840 I2C master peripheral
- Average current consumption below 3 µA
- RTC timekeeping with time resolution in seconds
- Support for Power-Fail Timestamp with time resolution in seconds
- Relatively low price of the component
- Has Zephyr driver support or at least C driver support
Possible RTC solutions
We found an multiple RTCs that fit our use case:
,but there is no Zephyr driver support for any of them, the best C driver support can be found for RV-3028-C7 RTC.
I know Nordic Devzone forum is not the best place to pose a question regarding other RTC solutions, but we are under time pressure and we would need your support choosing the best option to integrate with nRF52840 MCU with Zephyr driver.
Also if you know of any other RTCs that would be better suited for our requirements please let us know, thank you.