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LM3671 help


#1

Does anyone use or have experience with the LM3671 from TI.
http://www.digikey.com.au/scripts/DkSearch/dksus.dll?Detail&itemSeq=228583285&uq=636316255369528863
It looks like a sweet little package. I’ve stayed away from bucks in the past cause I’ve always found the inductors to add to much cost and have a large foot print. But this only requires a little 2.2uH inductor. The recommended inductor is this style.
http://www.digikey.com.au/scripts/DkSearch/dksus.dll?Detail&itemSeq=229156434&uq=636316286797093119

Page 16 of the data sheet says this about the inductor…
“A more conservative and recommended approach is to choose an inductor that has a saturation current rating greater than the maximum current limit of 1150 mA.
A 2.2-µH inductor with a saturation current rating of at least 1150 mA is recommended for most applications. Inductor resistance should be less than 0.3 Ω for good efficiency. Table 1 lists suggested inductors and suppliers. For low-cost applications, an unshielded bobbin inductor could be considered. For noise critical applications, a toroidal or shielded-bobbin inductor should be used. A good practice is to lay out the board with overlapping footprints of both types for design flexibility. This allows substitution of a low-noise shielded inductor, in the event that noise from low-cost bobbin models is unacceptable.”

Can anyone explain why one of these types of inductors wont work?
https://www.digikey.com.au/product-detail/en/LQM2HPN2R2MG0L/490-5114-1-ND/1893677

They’re so much cheaper and smaller. Have a found a little winner, or am I missing something?

Thanks in advance.


#2

If the specs are within range, then it should work.


#3

Pretty sure that type won’t work. The types listed in the datasheet are all wirewound types. The one you selected is multi-layer.

I may be wrong but I do not recall seeing that type used in switching power supply design. Most if not all are wirewound types.


#4

@ Dave McLaughlin - Yea but why is that? Induction is induction right…


#5

I’ve got the same gut feeling as Dave. What seems to good to be true usually is. But I’ll say it again "Induction is induction right… "


#6

Some good reading here but still does not explain why we can’t use the multi layer ceramic types. Film inductors apparently can be used.

https://blog.octopart.com/archives/2016/07/how-to-select-an-inductor

I am going to pose this question to a technical group on LinkedIn that I’ve found in the past can be useful for these sort of questions.


#7

@ stotech - Just my Two Cents, but since I require up to 3A @ 3.3v, I ended up looking at Murata for Power.

This line of devices LXDC2UR Includes both the filtering Capacitors & the Inductor, at comparable pricing at lower quantities…

https://www.digikey.com/product-detail/en/murata-electronics-north-america/LXDC2UR33A-122/490-5964-1-ND/3736606

The fact the device in total is smaller than most of the suggested inductors also makes it attractive, although at quantities approaching 1000, it does become the more expensive option.

Michael.


#8

Ok, everyone, thanks for the help. I stopped putting it off and just rearranged the pcb to take both foot prints. I’ve ordered both parts and will get back to you with the test results.


#9

@ stotech - Since you’re almost to 2.000 points, now might be the time to upload a profile pic so that people can tell you apart.


#10

@ Mr. John Smith -

Is otuplod similar to covfefe ?


#11

@ suitable1 - Yes, I need coffee. I’m falling asleep at the office. Didn’t even see that typo. :-[