Main and Backup Power

The power jack of the EM1206EV accepts "small" power connectors, 3.5mm in diameter. Use the APR-P0011, APR-P0012, or APR-P0013 power adapter supplied by Tibbo or a similar adapter with a 12V nominal output voltage. The adapter current rating should be at least 500mA. On the power jack, the ground is "on the outside," as shown in the figure below.

Alternatively, you can power the board through the V_IN line on the expansion connector. Two onboard diodes combine the power jack and V_IN inputs into a single line, which goes to the switching regulator. Clean 3.3V output produced by the regulator is used to power the EM1206EV, the EM1206 module, and optionally an add-on board plugged into the wireless add-on connector. This 3.3V power is available on the expansion connector as well.

The following drawing illustrates this power arrangement:

The EM1206 module features an RTC and a dedicated VCCB input for providing backup power when the EM1206EV is off. On the EM1206EV, the backup power comes from a supercapacitor on the bottom side of the board. The supercapacitor charges almost instantly and, in the absence of main power, supports the RTC for about a week.

Note that the supercapacitor is not connected to the V_CC line directly. The VCCB pin "expects" the backup power to have a nominal voltage of 2.5V. See Real-Time Counter in the EM1206 manual for details.