How to configure cell battery and USB power

[Serafino Convertini]

Hi to all,

this is my first public ticket ;)

I would power a nRF52840 on my custom board both with a cell battery (specifically CR2032) and the VBUS provided by the USB connection.
I was thinking to use two schottky diode in the way showed in the attached image with using the internal DCDC of the nRF52840 as in the development board.

But I'm not sure to use schottky diode since the voltage drop on the diode. In the proposed configuration for the nRF52840, I cannot find any solution that could fit with this question.

Has anyone done this task before?

Thanks in advance

[hmolesworth]

My grandfather used schottky diodes, nowadays there are better low-drop solutions. Have a look at these:

max40203 Ideal Diode

[Serafino Convertini]

Ok this IC could interrupt the voltage but how could I use in my application?

[hmolesworth]

Just replace the two schottkys with two MAX40203; EN is connected to corresponding supply (VBUS or VBATT). Highest voltage of VBUS causes lower voltage to be isolated. ie if VBUS is present there is no load on VBATT; if VBUS is not present VBATT supplies power. EN leakage is tiny. No other hardware or cpu interaction is required.

Edit: EN has an internal pull-up, so don't even need to connect it. Here is example with CR2032; duplicate for VBUS

//                   MAX40203                     
//              In  +-------+ Out    Battery +VE
//        +---------|       |--------------------0
//        |      EN |       |                     
//        |      ---|       |        Battery Gnd 0
//        |         +-------+                    |
//     -------          |                        |
//       ---            |                        |
//        | CR2032      |                        |
//        |             |                        |
//        +-------------+------------------------+