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SOT sizes

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bitman:
Is there a good chart where I can figure out what SOT sizes are available? Or rather, how they relate to one another?  This page https://en.wikipedia.org/wiki/Small-outline_transistor confuses me.

I needed to replace a DMMT5401 which had gone bad on my Raspberry Pi. I ordered SOT26 which was the smallest I could find, but it turns out to be almost twice as large as the original and is a hard fit in the same space. When I try to find out what "twice as small" would be, I don't get consistent responses, SOT23 comes in all kinds of odd derivations of 23 and I have no clue if that makes a difference.  What I would like to do is measure the old component and determine what size it is.

On a different note, searching on something SOT-23* on Digikey only gives me "obsolete" versions of this dual BJT - I wonder if that's just this component or that size just makes no sense? (It's very very small - I can imagine the issues getting something that small soldered on correctly).

T3sl4co1l:
Technically, this should do,
https://www.diodes.com/design/support/packaging/diodes-packaging/diodes-package-outlines-and-pad-layouts/
but it's rather verbose for a beginner question.

Oddly, I have a (promotional?) card hanging on the wall of my cube with examples of the most common packages shrink-wrapped to it.  I don't remember its title, and don't see a picture of one online, offhand.  Hmm.

If it helps, SOT-23 is almost always SOT-23.  Digikey is very good about collecting the various mfg-specific designations into the right package.  The higher numbers and letters and gibberish designations tend to be the microscopic unsolderable packages, which you'll probably want to avoid as a beginner.

If all else fails, read the datasheet and check the dimensions.  Designations don't mean a thing, what did they actually make?

And yes, shopping for, and footprinting, components is no easier as a professional.  Welcome to the real world...

Tim

Nerull:
SOT-23 is an extremely common size for transistors, it's certainly not "too small to solder".

SOT-26 is just another name for a 6 pin SOT-23



U14 on this board is the DDMT5401, and it looks like SOT-23 to me, and is about twice the size as the smaller SOT-523 transistors on the board.

bitman:

--- Quote from: Nerull on December 23, 2018, 01:55:15 am ---SOT-23 is an extremely common size for transistors, it's certainly not "too small to solder".

SOT-26 is just another name for a 6 pin SOT-23

U14 on this board is the DDMT5401, and it looks like SOT-23 to me, and is about twice the size as the smaller SOT-523 transistors on the board.

--- End quote ---

That's the B+ model - the B model (see attached) is using a much smaller version.  I've soldered those small suckers before - it's not impossible - it's just not easy. You really have to watch for temperature and airflow but it's workable.

spec:
Hi bitman


--- Quote from: bitman on December 22, 2018, 08:28:42 pm --- Is there a good chart where I can figure out what SOT sizes are available? Or rather, how they relate to one another?  .

I needed to replace a DMMT5401 which had gone bad on my Raspberry Pi. I ordered SOT26 which was the smallest I could find, but it turns out to be almost twice as large as the original and is a hard fit in the same space. When I try to find out what "twice as small" would be, I don't get consistent responses, SOT23 comes in all kinds of odd derivations of 23 and I have no clue if that makes a difference.  What I would like to do is measure the old component and determine what size it is.
--- End quote ---


--- Quote from: bitman on December 23, 2018, 03:07:03 am ---That's the B+ model - the B model (see attached) is using a much smaller version. 

--- End quote ---

The chip that you want to replace U14 is the BCM857BS, which has an SOT363 case (same function as the DMMT5401).
https://assets.nexperia.com/documents/data-sheet/BCM857BV_BS_DS.pdf
https://www.diodes.com/assets/Datasheets/BCM857BS.pdf

I think this is the circuit for your Pi, which must be a B3 model:
https://www.raspberrypi.org/documentation/hardware/raspberrypi/schematics/rpi_SCH_3b_1p2_reduced.pdf

As for rationalizing/understanding surface-mount case sizes, pin-outs, etc, forget it. It is a complete shambles in all respects, and is the cause of endless confusion, both in the amateur and professional worlds. The situation is a disgrace. :wtf:

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