A question on power source...
Our board has a number of 3.3V peripherals on it, and combined they draw more than the i.MX can supply. So, we had to add a separate 3.3V switching regulator.
Our board is externally powered from 5V, and we are currently using the VDD5V input on the i.MX to give it power. However, this results in some power being dissipated constantly through i.MX linear regulators, no matter what mode the i.MX power supply is in.
And plus another downside of using the VDD5V input is that the i.MX doesn't have a lot of tolerance (5% @ >100mA) for voltage droop on it (table 2-3).
So, since we have a stable 3.3V supply available, is it possible to power the i.MX23 directly through the VDDIO pin? This would allow more tolerance for 5V fluctuations since it would now be a function of the external 3.3V regulator, and it could possibly reduce the heat dissipation in the i.MX a little bit.
There is no battery in our application, so VDD4P2V doesn't matter, and we would just use the linear regulators to supply VDDA and VDDD and disable the DCDC converter (which we're already not using anyway). Looking at the diagram of the power supply (figure 32-1) in the manual, it appears that power coming in through the VDDIO pin should be possible since the final stage of the linear regulators are all pass MOSFETs.
It's a little unconventional, I admit, but I can't think of any reason why it can't (or shouldn't) be done.
Thanks for any thoughts,