I have a perplexing problem. I am trying to power an Argon exclusively via its 3.3v pin. Here are what I tried:
I created a “blank” sketch and flashed it to an Argon using DeviceOS 5.3.1
I connected the Argon’s EN pin to the Argon’s GND pin
I connected a 3.3v bench supply set for max 1.5 Amps to the 3.3v pin of the Argon
The Argon’s status LED does the following:
On initial power up, it is briefly solid WHITE
It then flashes GREEN two or three times and the cycle begins again (likely resets)
I have tried this on two Argons with the same results. With a 1.5A setting on the PSU, the power available should be more than enough. I have also tried on two different perf boards, again with the same results. I also setting the PSU to 5v and powering the Argon via the VBUS pin and that worked fine.
The output of the XC9258 3.3V regulator is connected to 3V3 and the CE pin of the XC9258 is connected to the EN pin.
I believe the issue is that regulator isn’t intended to be supplied with voltage on the output even when the CE is low. If VIN/VUSB isn’t powered, that will leave the chip unpowered, which may also cause issues.
The Boron does have a warning that you cannot power it by 3V3.
Unlike the Photon, this pin CANNOT be used to power the Boron.
However, now that I think about it, even though both have a XC9258, the Boron uses a load switch connected to the Feather EN pin instead of the 3.3V regulator CE pin, and that might be the difference.
I suspect that the note is incorrect and that applying power to the 3.3v pin (the Vout and Lx pins of the Torex XC9258) is not allowable. Looking at the voltage on the 3.3v pin, supplied by a bench PSU, I see this:
The XC9258 is clearly misbehaving and clipping the voltage low enough to cause a reset, especially when the radio is coming on. Perhaps the datasheet note should be updated to indicate that it is not possible to power via the 3.3v pin nor is it possible to bypass the XC9258.
The only alternative is to power with 3.6v on the Li+ pin, resulting in a horrible 1.6ma ULTRA_LOW_POWER sleep current. Bummer.
NOTE: The same problem occurs with the Photon2 which won’t even come on when trying to power from the 3.3v pin. In addition, the ULTRA_LOW_POWER sleep current is 35 mA when powered with 5v by VBUS!!!
@no1089, I tried with two Argons and I get a solid white to three green blinks cycle (it resets after the three blinks). I tried with both EN grounded and open with same results. And I use the same PSU as you. I will test with Argon out of the protoboard to be sure.
