I have been testing my carrier board with Enable sleep and I have not achieved the results I was hoping for.
The good news is that I can achieve very low power consumption (less than 1mA, I need to get my uCurrent back from a friend to be more precise).
The bad news is that I am seeing two problems which may be related.
- Periodically, using the Enable pin for sleep occasionally puts the Boron into a state where it no longer allows the battery to be charged:
Battery Charge doesn't work if starting when EN grounded
Boron Devices Stop Charging deviceOS@1.5.0
- Occasionally, the Boron will not wake even when the Enable pin is no longer grounded.
I am wondering if we could capture in this thread the right design requirements for using the Enable pin as I have looked across the forum and found conflicting advice. Some questions include:
- What voltages will the Enable pin tolerate? As it shuts off the 3.3V supply from the Boron it is tempting to power the RTC interrupt pin with voltage directly from the LiPo which goes to 4.2V. If I have the right data sheet voltages up to 5.5V should be OK. There are two series with different characteristics so not sure what the answer is here.
- What type of considerations are there for the pull up and voltages that drive the Enable pin. It seems it is pulled up to 3.3V. What happens when we apply 4.2V from our RTC interrupt pull up?
- What are the values of logic high and logic low for the Enable pin?
Here is the circuit I am using now using the MCP79410 clock and @rickkas7’s library. Do I need to put a MOSFET between the Enable pin and the RTC so it does not see voltage higher than 3.3V?
- Are there conditions that could cause the Boron not to come back on even if EN is high?
Any advice is appreciated.