Vin and coin cell usage with the dongle

[rananna]

The pin out diagram suggests Vin should range from 3.3V ~ 5.5V , while the schematic diagram flags Vin as ranging from 2.3~5.5V. Which one is correct? I would like to power the 52840 dongle with a 3v lithium coin cell like the CR2032. Is this possible?

[caizelin]

Hi, 2.3~5.5V is the operating input range of the Step-Down Converter. It's not recommended to supply 3V coin cell on Vin. A 3.7V battery will be better.

[rananna]

Thanks for the reply. While waiting for an answer, I tried a 3V coin cell and it seemed to work fine. I don't want to use rechargeable batteries due to the inconvenience of charging and low mah capacity comparing to a standard cr2032. Alternatively, could the dc-dc converter possibly work with 2 cr2032 cells in series at 6V? What are the issues with operating at 3v on Vin? If the nrf52840 soc vdd can be powered by 3v, would it be better to not use Vin to bypass the DC-dc converter and connect the 3v coin cell directly to the vdd (3.3v) pin on the dongle?

[gbuzogany]

All the limits for the nrf52 are available at the product specification doc: https://infocenter.nordicsemi.com/pdf/nRF52840_PS_v1.1.pdf

5.5V seems to be the max input voltage at the VBUS pin.

The MDK board also has a step-down converter that also seem to have an upper limit of 5.5V.

You would need to use another DC-DC converter to drop the voltage within the range, but there will be a penalty in energy consumption, so choose well.