

Reverse-engineering the TL431 - galapago
http://www.righto.com/2014/05/reverse-engineering-tl431-most-common.html

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userbinator
Great explanation. I still continue to be amazed at how _tiny_ the circuitry
in ICs is -- the TL431's die is only 1mm^2, and is on an older larger-size
process, but already contains over a dozen individual parts. The same area in
a modern nm-scale process would fit a few orders of magnitude more
transistors.

You can find plenty of examples of CMOS digital ICs reverse-engineered but
analog/bipolar stuff tends to be rarer; here's a bipolar digital IC (RTL
logic), in which one of the transistor's connections has suffered catastrophic
failure: [http://www.eevblog.com/forum/reviews/small-teardown-an-
old-t...](http://www.eevblog.com/forum/reviews/small-teardown-an-old-tek-ic/)

I wonder if most/all of TL431 produced have the same layout, and not just ones
from TI. There's a noticeable absence of any copyright date/manufacturer logo
on the die.

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kens
I'm very curious about the same thing, if all the TL431 have the same layout.
The two different TL431s in my article have the same layout, but don't match
the schematics in the datasheets. I don't know if they changed the design in
the past 26 years, or if there are different designs out there.

There's a small "TI" on the die, sideways above and to the right of the
TLR431A text, which I assume is for Texas Instruments, but the lack of
copyright is interesting. (I think chips are supposed to have a (M) for the
mask.) Since I ordered the parts on eBay from China, I don't know who really
manufactured them.

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joshu
I keep wanting to write him and ask if there is a way to fund his future
writing (funds to buy things to disassemble?) Everything he turns out is
fantastic.

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kens
Thanks for the kind words joshu. I'm reluctant to take money because then I
feel obligated to write an article reasonably promptly about something I'm not
as interested in, and it replaces the fun with pressure. (I hope that makes
sense.) But let me know if there's something specific you're interested in.
And if you want to donate, my daughter is raising money for wells in Africa:
[http://righto.com/change](http://righto.com/change)

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joshu
I understand. Do you have any projects you want to do but need
parts/hardware/etc? I liked the systematic analysis of power supply article,
but doing that sort of thing seems pricey.

I brought your daughter's wells fundraiser to an even 100%.

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kens
Thank you very much. That's very generous of you.

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sigterm
Does anyone know why the P and N regions conveniently show up as different
colors on the photo? Is this due to different oxide thickness?

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marcosdumay
One makes the entire dye with a kind of dopant, creates a oxide layer above
it, and remove the oxide where it should be doped again. Thus, I'd guess the
difference in color is due to the different thickness of the oxide layer.

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analog31
Thickness makes sense due to the same phenomenon as Newton's rings.

