Powering nodes (3.3V) with 18650/26650



  • Hello,

    I am trying to power my node with 18650 or 26650 battery and have the following issue. The normal voltage of a fully charged battery is 4.2V and this is not tolerable by atmega328p. I tried to use AMS1117-3.3, but for this dropout voltage is about 1.1V, which is no use. Any recommendation on LDO how to power 3.3V properly given that battery voltage may drop to 2.75V?

    The other option is to use 3.2V LiFePo4 battery (they provide 3.4V fully charged), but these are more difficult to come by.

    Any ideas please?


  • Hero Member

    In most cases I use a 662K regulator in one of its housing variations. This regulator is also used on many of the 5v compatible I2C sensor boards. You can even power your circuit from the sensor board if a connection is available.

    0_1457002952962_upload-ee41d5bd-e95d-4117-87d0-f1a2268a558a on the Slim AA node

    0_1457003413549_upload-2c2cd5a6-282d-4537-a9a1-cb00870c37eb

    BMP180 with regulator and 3.3v output/input (other type of LDO)



  • @AWI - Thanks. I was thinking about XC6206P332MR, but not sure how it behaves when voltage drops to, say, 2.7V?


  • Hero Member

    @alexsh1 Thats the same component (662k) ;-) Don't worry about voltages below 2.7v, your battery will be dead by then :cold_sweat:

    0_1457004531508_upload-292d9e16-d7b6-420c-b3e0-41a8e16c62ed



  • Just checked the datasheet:

    Output voltage range: 1.2V ~ 5.0V (0.1V increments).
    I can see they recommend using 1mF capacitors on pin 3 (VCC) and 2 (+3.3V)



  • @AWI Thanks - I am not concerned about below 2.7V as my battery PCB will cut it off anyway :)
    And yes I am aware this is the same component.

    Very useful diagram! Thanks
    Will be placing an order for XC6206P332MR


  • Hero Member

    @alexsh1 You will probably need the 3.3 version. Any ceramic capacitor between 100nF and 1uF will do (1mF = 1000uF, is a litte to much ;-) ) I hold a stock of 'multi purpose' 100nF capacitors.



  • @AWI Right - I have about 50 104 (100nF) in my stock - they are very typical for atmega projects.
    Thanks once again for your help


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