Author Topic: noob woes: finding an SMD inductor?  (Read 1225 times)

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Offline funbagsTopic starter

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noob woes: finding an SMD inductor?
« on: April 16, 2018, 05:33:59 pm »
Hey All,
I'm trying to source an SMD inductor (15uH at 1A), but I'm beginning to believe that every manufacturer has different package dimensions. At least I found very little consistency.

I'm totally new to this and have just been doing PCB design as a hobby for the last 6 months. I decided to try my hand at making a 12v to 5v step down power regulator with a mp1584en (to hook up to a car battery, and be able to power 1 USB device). The Data sheet tells me the value, and the relative pad dimensions, but not much more than that.

When designing the PCB, is there a relatively generic pad design/dimensions that will get me the most versatility for different mnfg's specs? Like 4040/1515? I worry because sourcing the parts that I need has been a battle in the past, and I don't want to be stuck with pads that don't exactly fit the part I have to end up using because my first choice is out of stock.

Thanks for any help.
 

Offline ovnr

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Re: noob woes: finding an SMD inductor?
« Reply #1 on: April 16, 2018, 05:55:48 pm »
It's not like you're mass-manufacturing these things. Plop down some pads that are close enough - too big is better than too small - and just deal with it. You don't have to have exactly right pads for large power inductors.
 
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Offline funbagsTopic starter

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Re: noob woes: finding an SMD inductor?
« Reply #2 on: April 16, 2018, 06:39:18 pm »
Thanks for the input, ovnr. I think you're right. I'll just put down pads I think are big enough... it just doesnt sit well with my OCD. I enjoy looking at the boards after their done, and small errors/hackishness like that drive me crazy.

I was just wondering how a professional would go about it? Not that I'll be able to do it that way.. haha

Thanks!
 

Offline dmills

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Re: noob woes: finding an SMD inductor?
« Reply #3 on: April 16, 2018, 06:51:44 pm »
Inductors are a pain in the arse.

My usual approach is to find three alternatives with Automotive Qualification (Tends to mean they will stay around a while) from ideally three different vendors (None of which is F&$&!*g Multicomp!) with footprints that I can combine into something that will work.

I still get burned by long lead times semi regularly.

Wurth have been good to me lately, but it really is a 'who has pissed you off least recently' thing, and Wurth tends to be very expensive thru distribution but not that bad direct.

Regards, Dan.
 
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Offline funbagsTopic starter

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Re: noob woes: finding an SMD inductor?
« Reply #4 on: April 16, 2018, 07:22:44 pm »
awesome, dmills! Thanks for the tip. I'll check out Wurth!

I know what you mean. In my noobishness I made the mistake or drawing pads for a PZT3904, but used the pin order from the through hole 2N3904 version, but actually ordered mmb3904 because everything else was out of stock, and on a 6 week lead, and I didnt pay close enough attention to the model number... hopefully a lesson I wont learn twice.  I now have 100 transistors I wont be using. hahaha

Thanks!
 

Offline T3sl4co1l

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Re: noob woes: finding an SMD inductor?
« Reply #5 on: April 16, 2018, 07:48:17 pm »
FWIW, the IPC acknowledges that there is no universal inductor footprint, so you have to apply their footprint design rules carefully to come up with a reasonable footprint.

In smaller values, conventional chip sizes are typical.  0603, 0805, 1210, 1812; but also nearby sizes, with different terminations (usually bottom pads instead of wraparound metallization), 0806, 1212, 1816, etc.

For footprints, bigger is usually better, yes.  As long as you can get a soldering iron around the biggest part you expect to use, you're fine!

Also watch out for manufacturers using different units for their numbering schemes: Vishay IHLP family are imperial (IHLP2525xxx = 0.25" / 6.3mm square), others are metric (Taiyo Yuden NRS6045 = 6.0 mm square, 4.5mm high).  Just name your footprints consistently (choose in or mm)...

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 
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