(1) Correct, if you supply VBAT and 3V3 through the connector, the Core module will work.
(2) The pinout of the 40 pin connector is in the datasheet. For a proper power supply use the green marked pins. (VBUS only if you add a USB connector):
(2)
Perfect, thanks a lot Bernd.
Is there any reason we couldnāt supply 3V3 and VBAT from the same 3.3v source? I know the RAK19007 has a min battery voltage of 3.3v so shouldnāt this be okay to supply that voltage to both? Is there a downside to doing it this way?
We donāt need to worry about handling power when USB is connected, just for operation from a battery source (that is regulated to 3.3v).
Welcome to the forum @KeithMon
The batteries used on the RAK19007 are 3.7 to 4.2V. If the battery voltage goes lower the regulator for the 3.3V is starting to draw a higher current, because its input voltage is below the specs.
For the RAK4631 itself, the 3.3V is for the SX1262 LoRa transceiver, VBat is feeding the DCDC converter of the nRF52 which generates its own 3.3V supply. The nRF52 datasheet says the nominal voltage should be 3.7V, but the range can be from 2.5 to 5.5V.
With only 3.3V on VBat I would expect a higher consumption of the RAK4631 due to its setup.
Thanks @beegee!
I noticed the SGM6036 regulator on the RAK19007 has a passthrough mode (100% duty cycle). It appears that when the battery voltage is near or less than the output voltage setting (3.3v), but above the UVLO threshold, the buck regulator will pass voltage straight through. This seems like it would use less power.
Do you happen to know how much extra power consumption weāre talking about when using 3.3v input to the nrf52 internal regulator?
Iām already pretty happy with the current draw when supplying 3.3v to the battery connector on the RAK19007. Itās about 35mW when using Meshtastic firmware (average consumption over a couple hours to account for periodic TX). Iām using an external solar battery charger module and itās actually feeding between 3.35v and 3.4v into the battery connector.
If the inefficiencies are already built into the overall power consumption Iām seeing (35mW) then maybe weāre talking about pretty small amounts of additional power consumption when supplying 3.3v to both.
Sorry, I did not extensive tests about the single power supply solution, I do not have RAK4630 here, only RAK4631. HW engineering said ~5uA higher consumption when using the single supply voltage.
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Thanks for checking. This helps me make an informed decision on the power circuit design.
For my application, 5uA isnāt enough to warrant two power rails.
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