Actually an 0402 wouldn't fit on the top side. I could do one on the back side, which would add via inductance, but anything I put on the top would have to be an 0201.
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Andrew Zonenberg (azonenberg@ioc.exchange)'s status on Wednesday, 27-Mar-2024 03:35:47 JST Andrew Zonenberg -
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Andrew Zonenberg (azonenberg@ioc.exchange)'s status on Wednesday, 27-Mar-2024 03:35:47 JST Andrew Zonenberg I don't work with 0201s all that much.
My options in inventory look to be CL03A104KQ3NNNH (0.1 uF) or GRM033R60J474KE90D (0.47 uF).
Both are 6.3V rated and would be operating at 3.3V.
The Samsung 0.1 uF loses 50% of its capacitance at 3.3V, thus making it 50 nF.
The Murata 0.47 uF loses 62% at 3.3V (due to the higher capacitance and thinner dielectric leading to higher field strength) but starts with much more capacitance - it's still 178 nF, about 4x the Samsung, so I'll go with that.
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Andrew Zonenberg (azonenberg@ioc.exchange)'s status on Wednesday, 27-Mar-2024 03:35:48 JST Andrew Zonenberg Also, I now have 2.2 GB of waveform data saved (almost, but not exclusively, from the rail validation work). Will be useful to be able to go back and look at saved waveforms and do A/B testing showing the impact of rework.
So now the question is, where do I go from here?
The SMPS is fairly straightforward, basically reference schematic for the LMR70503.
Layout wise, I see one potential issue: while the bulk caps (at least the nearest one) are connected to the chip on the top layer on the 3V3 side, the ground is not (only by vias to layer 2). So that adds a bit of loop inductance.
Not much, but some.
For initial rework, I'm thinking of shoving an 0.47 uF 0402 X7R across the C2/C3 GND/3V3 vias. Unless anybody else has better ideas?
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