Recommended operating conditions

[fglasmachers]

Thank you for sharing the design.

I am trying to understand the following sentence in your Readme:

The i.MX6UL/ULL/ULZ has several internal regulators that — while not strictly staying within recommended operating conditions — allows the entire system to be powered by a 3.3V and ~1.35V rail (provided you're using DDR3L instead of 1.5V DDR3).

What are the recommended operating conditions the design does not strictly stay in? Should I use a dedicated 1.35V rail for the DDR3L ram instead of sharing it with VDD_SOC_IN?

[jaydcarlson]

You should consult the datasheet for the part you're designing around, which will have detailed operating specifications. At 900 MHz, the i.MX6ULL has a recommended VDD_SOC_IN range of 1.375V to 1.5V. So yes, you could have a 1.35V rail for the DDR3L and a separate 1.4V rail (or whatever) for VDD_SOC_IN. For low-power applications, you'd actually want this rail to dynamically scale based on operating frequency, so you'd probably just use a supported PMIC, which will have the whole complement of regulators necessary.

However, for a wall-powered always-on design, that all seems a bit ridiculous, so I've always just used a single regulator for both DDR3L and VDD_SOC_IN rails and have never had issues on any of the boards I've designed with this strategy.