Multilayer Inductors SMPS - Page 1
Forum section: electronics / beginners

author: LIGHTSSOUT
author_rank: Newbie
timestamp: August 20, 2015, 09:45:08 am
content: HiI am making a PCB with a SMPS IC MCP1603 and am wondering if an Multilayer Inductor can be used because of space?The inductor I am looking at is a 4.7uH CPI0806J4R7R-10 from element 14.All I can make out from reading about them is Multilayer Inductors are less efficient.Can anyone give me advise on inductors in a SMPS.As I only started to play around with themThanks

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 20, 2015, 11:00:14 am
content: ...Maybe??Do you have any ideas what efficiency you're going for? Power level? Switching frequency? Voltage ranges (input and output)?Not to mention cost, size, availability and a number of other considerations.If you must have the most optimal converter, you can spend quite a lot of time digging through datasheets (few of which discuss matters of core and eddy current losses, particularly on the low priced parts) to pick the right part.If you just want something that works, as long as you aren't using old fashioned powdered iron toroids, you'll be fine.Tim

author: LIGHTSSOUT
author_rank: Newbie
timestamp: August 20, 2015, 11:34:50 am
content: Vin 4.5-5.5V, Vout 3.3VApproximate current draw ~ 20mASwitching at around 2Mhz.Would like it to be as efficient as possible.Thanks for your help

author: rimpelbekkie
author_rank: Newbie
timestamp: August 20, 2015, 12:46:02 pm
content: A common trap concerning inductors for SMPS is that all inductors saturate (magnetically) above a certain current. Above that current, the inductor roughly behaves as a resistor, with a value of the DC resistance of the inductor (ESR).When that happens you're in trouble as the inductor will not transfer power to the output anymore. When the no-load voltage is OK but it drops when loaded, you probably have a saturated inductor.I would select an inductor that can at least handle double the I_load so at least 40 mA in your case. Also the ESR should be low enough, I don't know how low, maybe less than 1 ohm ?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 20, 2015, 01:57:35 pm
content: Maybe one of these?http://www.digikey.com/product-detail/en/RLB1314-4R7ML/RLB1314-4R7ML-ND/2561400Claims Q = 100 (at 8MHz, presumably more like 50 at 2MHz).Awfully large, although at least it isn't very expensive.Who knows, it might push peak efficiency up to 91, even 92%.Why is it so important that efficiency be high as possible? You certainly aren't using the best controller if those last six milliwatts are that precious.I can't imagine many places where thermal would be a problem, at this power level. Perhaps miniature circuitry in a vacuum? You should use a hybrid for that though, much better conduction (bolted to a heatsink for eventual conduction or radiation) than PCB. Or find ways to avoid putting stuff in vacuum in the first place.If this is battery operated, going from 70% to 90% means going from 7 hours battery life, to 9 hours (assuming this is the only load, also). Two hours gained sound pretty valuable. Going from 90% to 95% only gets you another half hour, for significantly more effort and expense (now you're needing one of those $6/ea super high efficiency controllers that LT makes). Trying to push 99% will require significant design effort, size and cost (you have to do much of it discrete, because no one makes an integrated regulator that efficient), and net only another 24 minutes battery life. Effort that's likely far better worth spending on optimizing the underlying device, which might have even easier gains (e.g., implementing power management settings in all devices, not just the CPU?). Or get a 10% larger battery, which might not even break the mechanical design.Also, don't forget the leakage spec of the power controller. If you aren't using it at 20mA for 100% of the time, then its average efficiency will be significantly worse. Battery operated devices often achieve big gains for using a relatively crappy (70-80% efficiency?), but extremely low leakage (~uA current consumption between bursts of activity) regulator. Or, consider using ICs that can operate directly from the main supply without reduction.Engineering is the art of optimization, and there are a great many ways of doing that. Don't lose sight of the overall goal, and all the parts that go into reaching it. Well and truly maximizing efficiency, to the literal, absolute exclusion of any other consideration, is never a positive outcome when it comes to design. Likely, your application is much more diverse and nuanced than this singular constraint, so be careful what you say and think about -- it can mislead us in answering questions, just as well as it can mislead yourself down fruitless paths.Tim

author: LIGHTSSOUT
author_rank: Newbie
timestamp: August 20, 2015, 08:34:01 pm
content: Thanks for everyone's input.Only using that SMPS IC as a starting point.I am wanting to get as much life out of the battery I am using.For the design the efficient use of the devices battery is really important.As the PCB and battery cant be any bigger

author: LIGHTSSOUT
author_rank: Newbie
timestamp: August 20, 2015, 10:09:06 pm
content: Just wanted to add I mostly interested in SMD components.Looking through datasheets I have found one that looks promising.http://nz.element14.com/coilcraft/pfl2015-472mec/inductor-pwr-4-7uh-0-77a-20-50mhz/dp/2288748Any advice would be most appreciated

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 21, 2015, 06:57:57 am
content: Quote from: LIGHTSSOUT on August 20, 2015, 08:34:01 pmWell that's very important information. That means size AND efficiency are at least two goals!Anything else?You may consider noise output: that type of inductor is unshielded so will emit some switching waveforms to nearby traces/components. A shielded (powder or ferrite) type may prove better.Tim

author: LIGHTSSOUT
author_rank: Newbie
timestamp: August 22, 2015, 02:34:57 am
content: With shielding do you mean that the whole inductor should be shielded?Would you be able to give me an example of an SMT inductor that you would choose?Would this one be better shielded EPL2014?Getting a little bit confused as the datasheet says its shielded.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 22, 2015, 09:54:58 am
content: Yes, if the datasheet says it's shielded.The shielding isn't usually very good, but it's better than "open frame" types.Tim

author: LIGHTSSOUT
author_rank: Newbie
timestamp: August 26, 2015, 06:13:41 am
content: I think I have found one that ticks all the right boxes.It has lower DC resistance.Its Ferrite Cored.Also its shielded.http://www.farnell.com/datasheets/1697265.pdfThanks for your help I have learned a lot