Optional power on Vxxyy
ikskuh
Posts: 2
in Propeller 2
Does someone know if it's okay to not power a Vxxyy rail?
I want to build something that has a switchable power supply for a subsystem and i want to use that subsystems (switched) +3V3 signal for the Vxxyy pins, so the ADC measures against +3V3 of that subsystem instead of the global +3V3 rail.
But i'm not quite sure, from the datasheet it reads like it must always be powered on.
Comments
Yep, no problem with doing that, afaik. There are exceptions though: V2831 is needed at all times to maintain the internal clocking circuits. And V6063 is needed to maintain the reset circuit.
PS: For a low power sleep mode, I suspect reduced voltage on those two supplies when idling will be okay too. Especially if the crystal gets disabled beforehand. Then it's just running on the internal R-C oscillator.
Thanks! That means i can't really do what i want as i'd need all voltages below V5659 to be optionally enabled. If i can't make it work equally for all groups of 8 pins below pin 56, i better don't do that at all and just use a shared 3.3 V power rail for the GPIOs and ensure in software that they are high impedance when the associated power rail is disabled.
Nah, it's not about low power, but about having the correct 3.3V voltage rail for the GPIO pins so an expansion card of my system would have it's own 3.3V for ADC referencing.
There's no issue having multiple 3v3 rails. Some for analogue and some for digital for example. Every group of four I/O can potentially have it's own supply. All you need do is move the assigned I/O functions to allow for the oscillator requirements. How many ADCs are you using?