Is there a reason to use smps regulators over modules

Question

I'm just discovering that TI have switch mode power modules as well as regulators. For example they have the LMZ12001 which would be significantly easier to use than the TPS62150 regulator.

Elektor had a recent project based around the TPS62150 regulator and one of the comments on their website was a reader suggesting to just using a Murata OKI part. Less expensive for one thing.

Is there a good reason to use the regulator part over the module in any applications? Maybe in high volume as the cost might be lower but for the average engineer (ie: me) I can't think of any reason not to go the "easy-as-a-7805" route.

Answer 1

You have two main options: linear regulators or switch regulators.

Linear regulators are great if you are going from one low voltage to another, with little dropout and are pulling little current. Even at low voltages with high current, they're mostly OK. They are great after a switcher to isolate the switching noise and filter it out for you (they usually have a high rejection ratio). Problems happen when you want a lot of current at high drop out rates. A recent device I was designing.. I figured out that using a linear regulator would mean that for my desired 500mA load, and input of 14.4V and an output of 5V would have the device dissipating about ~3.5W of power. That's terrible.

Now, we come to switching regulators. Long story short, they are way more efficient. More efficient means less power wasted as heat through the components. The downside is that they are harder to design, harder to layout, and can potentially introduce a lot of noise into your circuit. Things are getting better, though, and we have more tools and designs available to us for free that we can pretty much drag-and-drop into our schematic editors.

Now, cost wise, linear regulators are one IC with maybe two - four supporting bypass caps and switchers can be up around four to eight components, maybe more. You have to source them all, etc etc. This is a great case for buying a power module / SIP module like the ones you've mentioned.

The power modules you see are all switching regulators. There would be no way to provide the power efficiency that the modules do without being switchers. Again, there are two categories here: chip-packaged switchers, we'll say, and PCB-packaged switchers. These are my terms, not industry terms.

The chip-packaged switchers are full DC/DC converters packaged in a single IC. You provide your typical bypassing capacitance on the input/output, and in some cases you might provide a resistor to adjust output power, maybe some other small basic discretes (resistors and capacitors) and voila, you have efficiently converted DC power. Things are great! The main downsides are cost and layout. A lot of the modules can cost well above $9 - $11 per module. Also, the layout can tend to be a little wonky. A lot of these modules are SMT with land grid array footprints or custom QFN footprints with big pads underneath. They aren't insurmountable to work with.. but it's a step up in footprint design from your basic leaded packages.

The PCB-packaged switchers work on the same principal (bundled solutions) but usually they are literally built on a PCB and you can see the individual components, etc. Sometimes, they'll be potted in tiny enclosures. Either way, they are switching regulators built from discretes rather than all packaged in a single IC. You can get them on the raw PCB with castellated connections, or in the case of the Murata OKI power modules, they have them in a SIP format to directly replace the classic 780X regulators. Pricing here is usually better than the chip-packaged switchers and sometimes, if you're lucky, they require no helping capacitors or anything... it's literally just plug and play.

All in all, switcher modules are nice. They give you high efficiency in return for a higher cost. The choice you make will most likely fall on cost and size. I, for example, chose to use the TPS84250 in a design. 5V/3A output from up to 50V input in about 200mm^2 worth of board space (including discretes) at about ~$14 total cost. To me, it's worth it to have the high efficiency but also to have a simpler BOM and simpler board layout. The Murata OKI power modules are nice, but compared to the TPS84250, I'd have to do a lot of work to fit one in my device... which is why I decided on the TI part because it's just an IC on my board... it's not an entire SIP module I have to cram in there and worry about vibrations and fatigue on the pins, etc.

Answer 2

You're right that volume costs come into the equation, and for some applications having control over the FET for higher currents and the switching frequency can come into play. It also gives you a few more options for component selection and placement which can be important for space-constrained applications.

That SIP module of course is much easier to hand-solder than the SMT part but would be more difficult for automated assembly on a pick & place machine. Also in high volume the inductors and other passive components cost cents so overall in volume it's normally cheaper to use switching controllers rather than modules.

But there's nothing wrong with the modules, they tend to make sense in < 100 type quantities if you can find one that meets other requirements and I've commonly gone down both paths depending on the project.