Please reply to following queries regarding RTC:
1. What is the voltage range of battery that can be connected to V_VBAT_BKUP pin (pin23 on the edison, pin 5 of J18 on the mini breakout)?
2. Can the -ve terminal of battery be connected to any common ground?
3. What is the power rating of the RTC circuit?
4. Can we connect rechargeable battery to RTC? What are the configuration settings to enable the recharge when power is on?
5. On Mini breakout board, can I connect the same 3.7V battery to J2 & V_VBAT_BKUP?
Let me know if this was helpful.
Thanks your for replying to the queries!
3. Section 4.13 is discussing the charging configuration settings for backup battery. I would like to know the typical power consumed by the RTC oscillator circuit.
4. Won't the battery connected to J2 be automatically charged while main power is On?
5. Will battery connected to J2 power up the RTC oscillator also?
"When you attach a rechargeable lithium-ion battery, the breakout board will recharge the battery whenever power is applied via J21 or J22, or via J3 (when the board is attached to a USB host)."
This means that both 4 and 5 are yes. As for question 3, it seems this information is not available on the document. I'll investigate further and contact you back soon.
We performed some tests on the power consumed by the RTC circuit. We tested the Edison breakout board with a standard lithium battery cr2032 attached to the RTC backup battery input (J18-pin5) and ground (J19-pin 3). When Edison is powered on (using a 12V power supply) the RTC power consumption is 1.2μA * 3.3V ~= 4μW, when Edison is off and has no power supply attached (just the battery) the RTC power consumption is 8.2μA * 3.3V ~= 27μW.