Safe 3V3 power for sensors

#1

Hi all,
I’m using a CubeCell dev board.

I have two groups of I2C external sensors which must be powered in a different way.

For one group I’m using Vext since I want to turn them on when needed.
But for the second group I need to have them “always on” since they wake up the module by interrupt.

from the block diagram I understand the difference between the Vs/Vin/Vdd pins, non of them will be “safe” for an “always on” sensor.

but … in the block diagram we have the “USB/Battery/VDD Power Supply Auto Switch System” which I suppose is the only “save output” we can use for “always on” external sensors, yet I don’t understand if we have the output of this block.

is there a pin to expose the output of the “auto switch system” so I’m sure I can always get a regulated 3V3 while I use Vext to switch on/off the remaining external sensors?

thanks

#2

You can use the VDD pin, whether you use USB or battery power supply, the VDD pin has power.

#3

ah! so this means that I did not understand the VDD pin functionality.

from the block diagram it seems to me that the VDD pin is an INPUT and NOT an output pin.
it is written in the schematic that a voltage of 3.3v is suggested, and I’ve seen other posts where it is suggested to add a 3.3v backup battery there.

are you saying that VDD is actually the output of the automatic power switch ?

thanks

#4

Yes, VDD is actually the output of automatic power switch. VDD input refers to the input voltage from pin VDD

#5

mmm sorry I’m confused now.

if VDD pin is an input for external power … where is the “other” VDD output pin to be used with external sensors?

thanks a lot for your help

#6

Srry, my meaning is not clear, when you use battery or USB power supply, VDD can output 3.3V, when you are not using battery or USB power supply, you can supply power to the development board through the VDD pin