USB Voltage - More important than you think?

I do most of my programming via Visual Studio Code – it saves on data charges by programming directly over the USB interface instead of OTA. To save wear and tear on various connectors, I’ve made a special USB cable with an in-line switch on the power wire. I noticed some time ago that the power coming over the USB appears to be necessary to power the Boron USB interface, since disconnecting the power to the Boron USB shut down the output to my serial monitor, even though the boron was being powered by a battery at the time.

This may be part of the reason why I discovered a strange issue: when trying to upgrade my development unit to 1.5.4rc1, I received a number of strange and inconsistent errors when trying to update. A bit of searching through the forum seem to indicate the boot loader was corrupt or out-of-date, so I found the binaries on Github and uploaded them. The problems persisted, and my code still would not load. Following a long and thoughtful coffee break, I connected to my computer via a USB 3.1 powered hub, instead of the normal USB 2.0 directly into the machine. The problems disappeared completely, the update flashed with no problem, in my code uploaded flawlessly. Just a word to the wise, if you see similar issues.

My USB input voltage at the board typically comes in at about 4.66V at the Boron when running on the USB to the motherboard (yup, that’s on the low side), and 4.75 when connected to the powered USB hub.

I would also welcome any feedback from our particle hardware experts. Thanks!

That is correct.
There is no boost converter to drive the 5V USB voltage when powering off a 3.7V LiPo. But the nRF’s USB block wants a fairly stable 5V (with tolerance) to reliably work.

BTW, is this an LTE or 3G Boron?
Especially for the latter it’s advisable to have a supply with at least 2A@5V rating (or charged LiPo attached) as the current consumption of the cellular modem may cause the voltage of a USB port to dip below the tolerated minimum.

LTE Boron in this case.

Identical behavior with and without battery connected when I was on the “weak” USB connection. Several days later now, everything is working great now with powered USB hub.

Thanks as always for your expertise, ScruffR.