I'm using a step-up DC/DC converter (https://www.torexsemi.com/file/xcl101/XCL101.pdf) in my circuit to boost a 1.5V AAA battery voltage to 3.3V. The 3.3V is powering an audio circuit, and I heard a lot of noise in the audio signal. I suspected the issue was a noisy power supply, so measured the 3.3V voltage on the scope, AC coupled:
Disregarding the spikes, the peak to peak ripple is about 40 mV. Would you expect this level of noise ripple at the output of a DC/DC step up converter?
This is the scope shot when I measured the AC coupled voltage across the battery by itself:
I'm not sure of the cause of the large spike, but it looks unrelated to the constant 40 mV noise on the 3.3V voltage.
This is the configuration I'm using for the 3.3V step up converter (from the datasheet):
The only thing I can think of that might help is using different capacitors. Right now I'm using ceramic 0603 capacitors (https://www.digikey.com/product-detail/en/murata-electronics-north-america/GRM188C81C106MA73D/490-7198-1-ND/3900421). The 3.3V step up converter's datasheet also recommends ceramic 0603 capacitors, however I noticed the specs for them indicate "Low ESL" (https://www.digikey.com/product-detail/en/tdk-corporation/C1608JB1A106K080AC/445-11201-2-ND/3948437). I'm not sure if using this recommended capacitor will make that much of a difference…could this be the problem?
Best Answer
Place RC lowpass filter on output of your power supply: 100 ohms and 100uF. This is a 0.01 second time constant, -3dB at 16 Hz, -20dB at 160Hz, -40dB at 1,600Hz, -60dB at 16,000Hz.
So use your scop probe across the 100 uF capacitor. CLip the scope probe GND lead to -side of the 100uF, and clip the probe tip to +side of the 100uF.
=============================================== Note the ESR and ESL will limit the far-out attenuation.
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That first screen shot shows 14 uS periodic ripple, or 70KHz.
A 0.01 second TAU RC LPF, at 15Hz F3dB, is 5,000X slower, thus might ultimately produce 5,000:1 cleaner voltage.