Inaccuracy of RTC at low or high temperature

[stars]

Hi:

When nrf52 series chips use 32.768KHz crystal oscillator as RTC clock source, the operation error is large at low temperature. Therefore, the following problems need to be consulted:

1. Whether the chip can realize temperature compensation, and if so, what methods can be adopted to ensure the accuracy of RTC at low temperature.

2. Is there a solution in the SDK? If not, what should be adopted.

3. If you want to work in extreme environments, which series of chips has advantages.

Hope to get the relevant reply as soon as possible, thanks.

[haakonsh]

When nrf52 series chips use 32.768KHz crystal oscillator as RTC clock source, the operation error is large at low temperature.

 What exactly do you mean by operation error? If you refer to clock drift then that is entirely controlled by your crystal. 

1. Whether the chip can realize temperature compensation, and if so, what methods can be adopted to ensure the accuracy of RTC at low temperature.

 You can either select a crystal that has better characteristics at the extreme ends of the operating conditions, or you can use an external clock source that has temperature compensation. 

From 32.768 kHz crystal oscillator (LFXO): 

"The following external clock sources are supported:

• Low swing clock signal applied to the XL1 pin. The XL2 pin shall then be grounded.
• Rail-to-rail clock signal applied to the XL1 pin. The XL2 pin shall then be grounded or left unconnected."

A low swing clock signal is typically an external crystal, whereas a rail-to-rail signal is typically an external clock IC. 

2. Is there a solution in the SDK? If not, what should be adopted.

There is no SW solution that can account for clock drift unless you have another device that you can synchronize your clock to. See https://devzone.nordicsemi.com/nordic/short-range-guides/b/bluetooth-low-energy/posts/wireless-timer-synchronization-among-nrf5-devices 

If you need a rail-to-rail clock source you need to set the apropriate bits in the LFCLKSRC register.

3. If you want to work in extreme environments, which series of chips has advantages.

All our devices use the same RTC.