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I'm planning to build/design my own STM32F407 chip based board for controlling a DIY audio amplifier.

I will have attached to this board some devices like LAN8720, SSD1309 based display and 3/4 LEDs.

But I'm struggling a bit to design the Power Supply for this board. I'm aiming to convert the Mains 230Vac power source to 5Vdc using SMPS Mean Well IRM-03-5 that provides 5V DC @ 0.6A, 3W.

Please find below the overview block diagram of the SMPS:

Mean Well IRM-03-5 Block Diagram

Mean Well IRM-03 Datasheet

As the chip works at 3.3v we need to further to reduce de voltage with a regulator. I was planning to use the TI TLV1117-3.3 but I'm struggling a bit to find the right specs for Cin and Cout capacitors.

TI TLV1117 Datasheet

What would be good values for my case? Assuming I can place the regulator close to the MW SMPS and I don't need 5V rail in the chip.

Is there any better alternative for regulator than the one I'm planning to use?

Maybe a bit silly question, there is a version of this SMPS, IRM-03-3.3 that already outputs 3.3v, if I use this one, can I skip the regulator or regulator is always needed?

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    \$\begingroup\$ ”Maybe a bit silly question, there is a version of this SMPS, IRM-03-3.3 that already outputs 3.3v, if I use this one, can I skip the regulator or regulator is always needed?” Most probably yes. Check the datasheet for the STM32 and measure the DC and ripple voltage in application. If within spec, then no issues. \$\endgroup\$
    – winny
    Jun 16, 2021 at 18:58
  • \$\begingroup\$ The datasheet of IRM-03-3.3 says the max ripple/noise is 100mVp-p. But could not find any reference for this in STM32 datasheet, how I can correlate to check if within good range for STM32 chip? \$\endgroup\$ Jun 16, 2021 at 19:37
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    \$\begingroup\$ Strange, there really should be a range of acceptable Vcc. I would bet on that it’s ok. You still need local decoupling capacitors close to your STM32 as per always. \$\endgroup\$
    – winny
    Jun 16, 2021 at 19:52
  • \$\begingroup\$ Yes indeed. Yeap I didn't mentioned but ofc I will add local decoupling capacitor as specified in STM32 datasheet. \$\endgroup\$ Jun 16, 2021 at 19:59
  • \$\begingroup\$ ”2.2.14 Power supply schemes • VDD = 1.8 to 3.6 V: external power supply for I/Os and the internal regulator (when enabled), provided externally through VDD pins. • VSSA, VDDA = 1.8 to 3.6 V: external analog power” \$\endgroup\$
    – winny
    Jun 16, 2021 at 20:06

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What would be good values for my case?

The datasheet says the specs were tested with a 10uF capacitor, this is probably fine for most applications. (One thing you could do is provide 1-3 footprints for bypass/power capacitors if you have area on the board and populate the ones you need to achieve the ripple you want). If you use tantalum or electrolytic then make sure the ESR of those caps are in the 0.2Ω to 10Ω range.

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  • \$\begingroup\$ I don't know very well what could be the ripple I want... What is the impact of the ripple on the STM32 ship or its components like ADC etc? \$\endgroup\$ Jun 16, 2021 at 19:39
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    \$\begingroup\$ For a purely digital design 10mV to 40mV could be acceptable, for analog designs it varies. You can calculate how ripple will affect ADC or amplifier noise with PSRR (power supply rejection ratio) \$\endgroup\$
    – Voltage Spike
    Jun 16, 2021 at 19:41

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