Author Topic: Advice needed about step-down regulator  (Read 343 times)

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Offline r-sTopic starter

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Advice needed about step-down regulator
« on: August 07, 2020, 03:06:43 pm »
Hey everyone,

I'm working on a few projects for which I need a step-down power supply. In the past I could always rely on an external supply, so I don't have any practical experience with DC-DC converter circuits and could use some advice.

Here's some context:
  • The load requires between 9 and 24 Volts, depending on the project. This is provided by an external power supply (some readily available wallwart).
  • The control part (ESP32 plus some other stuff) runs on 3.3 V. As I don't want two external supplies, I need a regulator. A linear regulator would waste way too much power, so a step-down regulator is required.
  • These are hobby projects; I'm not going to sell them => regulations (e.g. about EMI) aren't that important.
  • I want one general purpose 9-24 V to 3.3 V step-down circuit (max. Iout: 2A), instead of one optimised circuit per project. As a hobbyist, I'd rather spend a few cents more than needing a huge inventory of parts that are only used in one project.

Requirements for the step-down circuit:
  • Reasonable efficiency. I'd really like >90%, but don't think that's realistic when stepping down from 24 V to 3.3 V.
  • Small footprint area; I'd like to keep the PCB small.
  • Maximum part height: about 10 mm.
  • Must be solderable with iron or hot air rework station. I can handle QNFs and similar packages. Grid arrays (LGA, BGA) I want to avoid.

I looked around for ready-made power modules. Recom has a few nice 3-pin THT devices, however above 1A they are just too high; the smaller parts all have grid arrays.
I browsed Digikey, but haven't found anything nice that matches my requirements. Maybe I've missed something? If someone could point me to suitable modules, that would be great.

Assuming I'll have to build the circuit myself, I could need some advice:
  • Which regulator ICs should I consider?
  • I had a look at TI's parts with integrated inductor (e.g. TPSM53602). Those look nice; the integrated inductor keeps the footprint small. Any reasons to go for an external inductor instead?
  • Any other TI parts I should consider? I particularly like TI, as I find WEBENCH quite helpful.
  • Any other manufacturers I really should have a look at? The manufacturer should have a tool similar to WEBENCH.
  • How much should I care about EMI? WEBENCH offers EMI input filter circuits (CISPR 22 and 25). Should I add such a filter? As mentioned above, I just want to avoid causing any interference for myself or my neighbors, so how much filtering is enough?

And finally: are there any other important questions that I should ask but haven't so far? ;)

Now please let the advice flow; I could really use it :)

Cheers,
Rolf

 


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