Xenon 3.3v output when EN grounded

I am powering a Xenon board via the USB connector and trying ti use the EN pin as an “on/off” switch.

When I measure the 3.3V pin on the Particle Xenon with the EN pin grounded, I see 1.0V not 0V as I expected. It reads 3.3V and operates normally if EN is not grounded.

Am I misinterpreting the function of the EN pin? I thought ti disabled the regulator and 3.3V should go to 0V to effectively "turn off " the board.

BTW -I checked an Argon board and found the same behavior.

Do you have any external circuitry attached to the 3.3v pin or are your measurements with just a bare chip, in a breadboard (not in foam or any other medium), connected via USB?

I have tried it with and without the external devices – The 3.3V output is the same.
EN not Grounded – 3.3V
EN grounded - 1.0 V

it is connected via USB for power

1 Like

After a bit more reading, it looks like the power regulator on the Xenon is working as designed
According to the datasheet the output voltage only goes to ~.8 V when the CE (EN pin) is Low.

full datasheet

Is it problematic to have a Xenon connected to a featherwing board with the 3.3V sitting at .8V for a long period of time? Should we avoid using the EN pin as an On/off for the Particle Boards?

The situation i ran into this was was using a Particle Xenon on an Adafruit TFT Featherwing which uses the EN pin as an On/Off switch.

Interesting find.
I confirmed with a Xenon having 0.460V on the 3V3 pin in stand-by (EN pin Grounded).
I never saw 0.8V that you mentioned.

However, the Xenon’s current in stand-by mode was measured at 29.6 µA.
I quickly grounded the Xenon 3V3 pin (while in stand-by) and the voltage returned to 0.460V immediate after, which I didn’t expect.

Leaving the 3V3 Pin grounded increases the stand-by current from 29.6 to 30.1 µA.
In my mind, that means that only 0.5 µA (and only @ 0.46V potential) is available to sneak around your peripherals when the Xenon is shut-down via EN Pin. But I could be misunderstanding something.

I see as much as 1.2V on the Xenon – At first application of power (via 5V USB) with EN grounded it goes to ~.8V but then if I open then reground EN, it goes up to 3,3V then back down to 1.2V and stays there.

I’m puzzled…

BTW -the device is working fine…when EN is not grounded.

Sorry, I should have mentioned I was powering with the Li-Po connector.
Will you be powering the final project via USB connector, or battery ?

But at first glance, it doesn’t appear that it should matter … as long as you’re not powering the Xenon via the 3V3 pin directly by an external source .

Ah – If I use a Li-PO I see similar results to what you reported ~.46V with EN grounded.
Thanks for the clarification.

1 Like