I have zero experience with real world inductors. I need 47uH for an NCP1402 step up converter. Looking at Aliexpress, there seem to be appropriate inductors in 0603 and 0804 format, aside from the usual coils. Since I am low on board space, I would like to use those. I guess there are current limitations for those small footprints? What are they, commonly? Anything else to take care of?
In this application you have to discover from you circuit what PEAK current the inductor will have to handle, and choose one rated significantly higher that that.
Allan
Ok, ALiexpress vendors of course don't give any specs as usual. From what I see for similar products at digikey, the current rating of those small SMD inductors is VERY low.
Can anyone suggest a China inductor with a footprint as small as possible that can work for the NCP1402 (up to 200mA), to power an 8Mhz ATMEGA and an RFM69 module (up to 130mA in occational 2ms peaks)?
The ripple current through the inductor will depend on the output capacitor, the desired voltage ripple and the frequency chosen for the converter.
Higher frequency will always give smaller ripple current and smaller components. If you are that tight on board space, investigate the highest frequency you can achieve.
The peak switch current for the NCP1402 is about 200mA, and they recommend 47uH.
I'd go for at least 300mA rating.
Get searching.
Alan
For power conversion you require a ferrite gapped inductor of suitable size for the power being
converted (depends on frequency), and with a high enough current rating that it doesn't saturate.
Err on the large size is good unless you want to figure out temperature rises based on ferrite
material specifications, and such.
The tiny smt inductors you found are probably RFCs [ rather than power inductors which carry
much larger DC currents ]
I feared that ... Than I guess there's no step-up for me. I have about the area of half a CR2032 and the height of a SOT82 package. Seems that is too small for a an appropriate inductor. (More concerning height than area)
It is for the next revision of my MySensors Keyfob and needs to go into a premade Keyfob enclosure.
Somehow, cannot get the Openhardware page to update (if it shows a panelized PCB, it is the old version), but here is the Github repo, if anyone is interested.
Got an internet connection?
Google 'low profile inductors'
My first hit gave me this.
http://ctparts.com/media/catalog_pdf/product/ctmpa121206f.pdf
47uH, 3x3mm, 1.5mm high, 0.39A rating
I'm sure there are loads more.
Allan