All,

I dug into the CAN-Do circuitry today.  The CAN-Do module uses a Maxim max1836 switching down-converter.  I found the following quote in the spec sheet, "Commonly, instability is caused by excessive noise on the feedback signal or ground due to poor layout or improper component selection.  When seen, instability typically manifests itself as ‘motorboating,’ which is characterized by grouped switching pulses with large gaps and excessive low-frequency output ripple during no-load or light-load conditions."

It reminded me of the waveform I captured earlier from CAN-Do inductor, L3. (See the waterfall display below.)  Those are definitely grouped pulses with large gaps.  Notice also that there is tremendous splatter over a large bandwidth that can just be seen as faint horizontal lines.

I’d like to propose an alternative – Move the switching down-converters out to the power distribution and management area and feed DC to the payloads at an appropriate voltage so switching power supplies can be removed from all analog payloads.  This would go a long way towards cleaning up what is shaping up to be a nasty situation.  It’s just not good design practice to bundle switching supplies with low-level analog signals.

73,

Juan