RTC backup battery on ELS61 | Thales IoT Developer Community
December 14, 2021 - 4:41pm, 921 views
I'm using an ELS61 module and I have to add a backup battery for the RTC. The documentation says that the maximum voltage on VDDLP pin is 1.9V, so I should use a 1.5V battery, that is not a typical value for RTC.
Can I have a more detailed documentation, and possible an application schematic?
Alessio
Hello,
We probably don't have more detailed schematics for this scenario.
I've found the following advices in a discussion with some other customer:
We generally recommend to use 1k resistor and a big capacitor with small leakage current. Especially if short power downs are expected.
For example something like this: DRL105S0TF12RRASP
For long power down periods (weeks) the battery could be more appropriate. For example TS621E-FL11E should do the job (it can be charged with 1.8V if it's fitted with 4300R resistor).
If you have any concerns, please share here.
Best regards,
Bartłomiej
Thanks for your reply.
In this post you says that the RCT accuracy is very low in the EHS6 module:
https://iot-developer.thalesgroup.com/threads/real-time-clock-drafts-ehs6
If the ELS61 module has the same problem, the only solution for us is an external I2C RTC. Do you have information about the accuracy?
Thanks,
Alessio.
Hello,
We don't have any information about the accuracy in our documentation. I don't remember any problems with the accuracy for this module. The accuracy depends at least on the temperature.
If the accuracy is crucial for your solution I think that you may need to test it with your use case. To ensure the best accuracy you may add time synchronization with a network time server or wireless network. It is possible to enable time synchronization with the network with an AT command. But not all networks may support it. It is done automatically on the network registration.
So the approach would depend on your use case.
Regards,
Bartłomiej