- 5V to VUSB, or
- 3.3V to VIN, or
- something else if none of those above are thought to be a good idea for my application in the long term.
I am trying to work out the pros-and-cons for long-term-reliability of those two main powering options given that my device will mostly be in a (~40deg C?) environment for ~10 years.
Among other statements, the instructions on powering the D-series: https://pybd.io/hw/pybd_sfxw.html#power-supply
andYou can power the PYBD via the VUSB port (see X-positions). The voltage on this port must be between 4.8V and 5.2V. This port contains a protective diode and a 1A fast/0.22Ohm fuse.
3.3V on VIN pros and consYou can power the PYBD via the VIN port (see Y-positions). The voltage on this port must be between 3.2V and 4.8V. ... For best performance provide 3.4V on VIN (3.3V is also ok but 3.4V will benefit from LDO filtering).
So far as I can see, the 3.3V option has the benefit that it will not waste power as heat, which could lead to my board not running unnecessarily warm in what will already be a warm environment. However I am alarmed that 3.3V sits at exactly the level at which we are told LDO filtering will no longer happen, and only 0.1V away from the recommended absolute minimum lower power voltage limit of 3.2V. Who knows: with a small amount of derating it would not be impossible to imagine that the embedded PS could give a little less than its rated 3.3V at times ... How sensitive is that 3.2V lower limit? If I am right up against it, and in a somewhat noisy environment (coupling from mains) will I be almost ensuring that my pyboard has unpredictable glitches once per month and works unreliably? Does anyone have any experience with that?
5.0V on VUSB pros and cons
This has almost the reverse pros and cons of the other option. Brown outs from marginal undervoltage are presumably very unlikely, but correspondingly I assume that the pyboard regulator will get hot over time -- though perhaps not hot enough to cause me problems??
What sort of temperature difference do people see for 5V vs 3.3V powering schemes? Anything noticeable or basically imperceptible?
If (as the notes say) "3.4V is best" then I will have to do more design work as I can't get any off the shelf power supply that would suit me at voltages between 3.3 and 5V. And I'm not very good at desiging power supplies, so I don't want to go there unless I really have to.