This scope pic is from the 3.3V on my MC4X15A – Universal Motor Controller. The MCU is running and I have the 0.33F Supercap mounted. Ca 200mV point to point ripple is to much for my taste, but it works and this is far better than I have measured out of the Lab PSU’s. I am also using the DPS5005 in this case just to see if it worked at all.
This started as a small experiment as I wanted to see the effect of swapping out the inductor on my LMR14206 – I obviously need to revisit my lab PSU design. The lab PSU and scope is located next to each other on the shelf and I only need to switch it on to introduce noise – I don’t even need anything connected. I obviously have introduced a noise source in my lab that I need to figure out.
This is a set-back because I have been extremely happy with DPS5005 before this.
Returning to LMR14206 I seem to be stuck with 200mV point to point ripple. I am also puzled to as why I see the same ripple on 12V and 3.3V, but I will get some help investigating that. The actual reading on the scope pic is much higher, but that is the external noise. The ripple signature will differ a bit from using DPS5005 versus Thaoxin as they introduce different noise pictures. The small spikes you see above is the 1.25Mhz switching frequency of LMR14206 – and just for the record – it’s no problem adding a filter on the 12V and remove this ripple, but that add PCB size and complexity – part of the objective here was small space.