ke7c2mi
DIIDevHeads IoT Integration Server
•Created by ke7c2mi on 9/9/2024 in #pcb-and-analog
Designing an SDR with PoE Power Supply: Synchronizing SMPS and Managing Heat and Noise
In this design there are 2 conflicting concerns - heat dissipation and noise. Ideally, I could just use the LM5070, drop to 3.3v and LDO everything from there, then the system only has a single SMPS and there are no issues with them interacting. In practice I think this will lead to burning up too much power on the board and things getting hot (whilst we are only talking about a couple of watts here, it's in addition to the power that's actually used, I am currently aiming for the board to be 50mm x 150mm and I'd like to avoid needing an enclosure and heat pad to keep it under control)
So - I think I need LM5070 to drop PoE to some intermediate voltage, and then some multiple buck PMIC to drop to the actual voltages I care about.
As I understand it, when we have two free running buck converters we can get "wobbly harmonics" from their interaction, where if they were locked together then the harmonic pattern would be static - which would be preferrable for something which wants to measure RF signals.
I've found some suitable parts for this, but the one I like the most, TPS65217A (I would like DVS, happy to talk about this - the thought is that it will allow me to play with any noise I find on the board and tweak power consumption.. maybe I can try to overclock the ECP5 some day). The problem I found is that it doesn't have a clock input or output, so I could never synchronise it against the LM5070. It also doesn't have any way to tweak the oscillator speed - with the LM5070 there is a clock input that I could drive back from the FPGA after boot which would let me twiddle the frequency, in theory moving any harmonics.
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