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Moving from small arduino applications to higher-power applications for work, I've had to switch from using simple linear regulators to switching boost/buck converters any time a different voltage to what is available is required. This has been much more of a learning curve than I anticipated; things like switching frequency, inductance and capacitance values all need to be taken into account, and there are almost always several external components (for example, the inductor) required for the converter to function.

My question is, why are these additional components almost always external? I'm not complaining, I've been learning a fair bit from the switch and it's not too bad a curve, I'm just curious as to why there seem to be no plug-and-play ICs (at least not that I've found for 24V, 3A output, correct me if I'm wrong) like there are for smaller linear regulators.

My guess would be too much heat generated?

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    \$\begingroup\$ Is this the "integration level" you're thinking about? ti.com/product/TPSM84209 \$\endgroup\$
    – Marcus Müller
    Nov 7, 2019 at 22:40
  • \$\begingroup\$ @MarcusMüller Pretty much, that seems quite impressive for only 4mm x 4mm \$\endgroup\$
    – Isaac Middlemiss
    Nov 7, 2019 at 23:44
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    \$\begingroup\$ Analog Devices has some all-in-one PMICs called µModule. Some of them look rather funny with the inductors tacked onto the top of the package. \$\endgroup\$
    – JYelton
    Nov 7, 2019 at 23:46
  • \$\begingroup\$ @Isaac Middlemiss There is a 2.9mm x 2.6mm DC-DC module (ti.com/product/TPS81256). \$\endgroup\$
    – Arseniy
    Nov 8, 2019 at 9:35

3 Answers 3

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It has to do with the limitations of silicon.

You can easily make lots of transistors in silicon, and connect them together.

Resistors and capacitors, particularly ones with any precision, are harder, and you can't really make them to handle any appreciable energy. It can be done, but they take up lots of space (I'm not sure how things stand now, but at one point the typical internal compensation cap for a unity-gain stable op-amp took up most of the silicon).

Inductors are right out. You need low-resistance windings, you need a magnetic core, you need size.

Which is why your switching supply has a chip that does everything that can be reasonably done in silicon, then it's surrounded by (relatively) big capacitors and a (relatively) big coil.

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    \$\begingroup\$ Nice and succinct. I'd add that the useful inductor's magnetic energy is stored in interstitial vacuum space and, given fixed relative permittivity, the volume needed is proportional to peak stored energy. That said, they do make all-in-one modules like the PM-03 (AC to DC in this case, though.) The reason I write this is that the OP may not be aware; and, despite their size, they may be perfectly suitable for the OP's interests. \$\endgroup\$
    – jonk
    Nov 7, 2019 at 23:35
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    \$\begingroup\$ You can find it yourself by looking closely at the equations, either in Feynman's 2nd lecture volume or else by a very simple analysis of the usual electronics based inductor equations. I work with physicists all day long and what forced me to "think" was an almost abusive comment from a physicist to me when I exhibited my own lack of thoughtfulness about the topic, more than 30 years ago. It was a quick slap in the face and he didn't elaborate. But that event forced me to "go look." Then I saw it, easily. (If you want, I can write more.) \$\endgroup\$
    – jonk
    Nov 7, 2019 at 23:41
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    \$\begingroup\$ How do devices like this one from Marcus's comment above manage it then? Do they lose precision? \$\endgroup\$
    – Isaac Middlemiss
    Nov 7, 2019 at 23:53
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    \$\begingroup\$ @IsaacMiddlemiss, they hide an inductor (and maybe a discrete capacitor) inside the mold compound. \$\endgroup\$
    – The Photon
    Nov 8, 2019 at 0:19
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    \$\begingroup\$ @IsaacMiddlemiss you'll see that's called a "module", not an "IC". That word (plus the height and overall large size) lets you know that there's a "regular old" circuit inside of that package. \$\endgroup\$
    – TimWescott
    Nov 8, 2019 at 0:25
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There are also this compact micoModules available, for example from Analog Devices [Linear Technology].

It integrates controller, inductor and capacitors inside one package: enter image description here

The reasons for using such modules are:

  • Lack of resources for SMPS development
  • High Integration for low PCB area applications
  • High resistance to mechanical shock
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Fully integrated DC-DC convertor is often called "DC-DC module" (examples). DC-DC module are quite common on sale. If you look on KC705 (Kintex-7 evalution kit) you will see four fully integrated DC-DC moduls on the right side.

Notably that many manufacturers of capacitors make their own DC-DC moduls with components that are not sold.

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