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I get that smaller capacitors have lower parasitic inductance and resistance compared to larger capacitors. And lower parasitic impedance allows the smaller capacitors to be more effective at filtering out high-frequency noise.

Although, I am just using a VS1053 to emit a basic ringing sound. It's not some complex MP3 tune. There are very short traces between the voltage regulators/MCU and the CODEC. Do I need any bypass capacitors at all?

enter image description here

The datasheet of my LDO only has 1uF capacitors:

enter image description here

The supply will probably be a Meanwell IRM-90-24 connected to an VXO7805-1000 (5V) connected to an ESP32 for the 3V3. (The MIC5504-1.8YM5-TR providing 1.8 V will go off the VXO7805-1000 too.)

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  • \$\begingroup\$ You're asking what you can get away with. That single IC has 12-odd MHz external clock, 36-odd internal and it's rails will be held up fine by the 1uF and regulator if it's reasonably close, you'll just get more switching noise. But it's impossible to answer without knowing the supply going to the LDO regulator. If the regulator's running from a battery then the only high-frequency noise is generated by the load. If the regulator's supplied by a noisy mains SMPS up a long unscreened twin-flat cable then there's plenty of noise needs filtering. Please edit your question to explain the supply. \$\endgroup\$
    – TonyM
    Commented May 18, 2023 at 15:31
  • \$\begingroup\$ Those links are not actually related. Those are bypass capacitors for a digital circuit. Search bypassing on this site for why they're needed. \$\endgroup\$
    – user1850479
    Commented May 18, 2023 at 15:32
  • \$\begingroup\$ ...or search for 'decoupling' which is the other common term for them \$\endgroup\$
    – TonyM
    Commented May 18, 2023 at 15:39
  • \$\begingroup\$ The supply will probably be a Meanwell IRM-90-24 connected to an VXO7805-1000 (5V) connected to an ESP32 for the 3V3. (The MIC5504-1.8YM5-TR providing 1.8 V will go off the VXO7805-1000 too.) \$\endgroup\$
    – adamaero
    Commented May 18, 2023 at 16:08
  • \$\begingroup\$ Please edit this (and any) new info into your question, don't post it in comments. Otherwise, readers have to piece together the full question from scattered fragments. Thanks. \$\endgroup\$
    – TonyM
    Commented May 18, 2023 at 18:03

2 Answers 2

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The device is not 'just audio'.

On the schematic in the data sheet you link to, you will see that there are as many small capacitors shown as there are power pins on the rail. That's a convention to mean that each power pin needs a capacitor, mount them as close to the power pin as physically feasible, and with a short connection to the correct ground as well, usually just the appropriate ground plane. This is so that the logic parts of the chip have an electrically 'stiff' supply on every pin. That's so the digital pins can draw their current steps with rise times of ns without disturbing the supply. These capacitors are in addition to the larger caps you have near your regulator.

Do you need them at all? Why not try without, it may well work.

How much would you save by leaving them out? A few pennies, and a few mm2 of board area.

How much could it cost you to leave them out?

  • It could cost you another spin of the board when you find you need them, and weeks of delay.
  • It could cost you weeks of troubleshooting to find out why things aren't working.
  • It could cost you months of troubleshooting if things don't work but just from time to time.
  • It could cost you customers if things work in the lab, but don't work when delivered to the field, that's a very nasty one.

It's your call, but I would put them in.

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  • \$\begingroup\$ I immediately got the quote from Dirty Harry but it's a 51-year-old film and many others on the site won't. Then, taken at face value, it's a bit of a nasty insult at the end of your post so I'd delete it. Sorry to spoil what's clearly just intended as a bit of fun, don't mean to sound joyless... :-) \$\endgroup\$
    – TonyM
    Commented May 18, 2023 at 15:37
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    \$\begingroup\$ @TonyM Is it 51 years? Seems like yesterday! \$\endgroup\$
    – Neil_UK
    Commented May 18, 2023 at 15:42
  • \$\begingroup\$ I feel even worse now...the slightest sign of someone having a laugh for two minutes amidst all the stern seriousness has to get stamped on... :-/ :-D Cracking film. In a spoof of actions 80s film, Charlie Sheen blazes his SMG away at a baddie in a shop chase then corners him, saying "I know what you're thinking: did I fire 373 shots or 374?". \$\endgroup\$
    – TonyM
    Commented May 18, 2023 at 15:42
  • \$\begingroup\$ I'm not far out of undergrad and the context of that phrase is definitely familiar to me and my peers; I think a safe balance might be "to quote the Dirty Harry film, 'Do you feel lucky, punk?'" to make it clear it's a reference, while still carrying its lighthearted and relevant intent. \$\endgroup\$
    – nanofarad
    Commented May 18, 2023 at 15:44
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    \$\begingroup\$ @TimWescott The analog and digital grounds are anyway connected together as close to the chip as possible (says in the data sheet), maybe by just connecting all ground pins to a single ground plane. The pin names are just for determining which ground pins are used for noisy digital logic and which for analog reference to reduce noise, and how to arrange the power supply and the analog and digital components around the chip for best analog performance. \$\endgroup\$
    – Justme
    Commented May 18, 2023 at 16:12
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Maybe not for an audio circuit, but that's not an audio circuit.

That's a digital CPU/DSP running at tens of MHz, max 55 MHz.

It has got nothing to do with what audio a built-in oversampling sigma-delta DAC happens to output.

Each power pin has one small capacitor right at the IC for all power pins.

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