Electronic – How to verify that the 3.3v power rail meets the requirements for an Ember EM357 SoC


I've built a circuit that is going to supply 3.3v to a CEL Meshconnect Mini Zigbee module and now I want to test and verify. The only two things I know to look for is:
-Make sure it's actually 3.3v
-Find out how much ripple there is

Can any basic oscilloscope tell me how much ripple there is?
How much ripple is too much for a Zigbee SoC?
Are there any other factors(i.e. noise) that I'm not taking into account?
Am I over thinking this?

Best Answer

It's more important to know how much current the module can draw. If your DC source isn't up to the task, the module will collapse the rail and all sorts of interesting behaviour can ensue (hiccupping, brown-out, etc.)

Industry practices for power supply ripple measurements must be done with a short probe (no long ground lead) or a direct-connect coax with proper termination, with 20 MHz bandwidth limiting turned on, and a combination of ceramic and electrolytic capacitors at the measurement point to attenuate CM noise and give you a 'true' indication of what the ripple is. In industry, it's common to use a 10 microfarad electrolytic capacitor in parallel with 100nF ceramic.

How much ripple your module can actually tolerate is hard to judge unless the manufacturer has specified it. Less is generally better when it comes to microcontroller-based gadgets, especially ones that do a lot of analog-to-digital conversion.