
Reverse-engineering the TL431: the most common chip you’ve never heard of (2014) - pngmangi
http://www.righto.com/2014/05/reverse-engineering-tl431-most-common.html
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magicalhippo
Richi's Lab[1] also contains a large number of pictures and analysis of
decapped ICs. He's also documented his decapping process[2] which uses an oven
rather than the dangerous acids, making it more approachable.

It's all in German, but Google Translate does a good enough job that it's easy
to follow.

He's got a very interesting comparison of STM32 originals and clones, as well
as various voltage references, 555 timers etc.

A personal favorite is the LTZ1000[3]. The die is a piece of art.

[1]: [https://www.richis-lab.de/index.htm](https://www.richis-
lab.de/index.htm)

[2]: [https://www.richis-lab.de/decap-ofen.htm](https://www.richis-
lab.de/decap-ofen.htm)

[3]: [https://www.richis-lab.de/REF03.htm](https://www.richis-
lab.de/REF03.htm)

~~~
mrunkel
Particularly for German, I highly recommend
[https://deepl.com](https://deepl.com) it does a much better job than google
translate.

~~~
magicalhippo
They don't seem to support translating a whole page, or am I missing
something? Copy/pasting is tedious.

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ggm
there is something reassuringly "analogue" about how these artifacts get over
the technology limits of diffusion/mask/layer systems, to make building
blocks:

"I need a resistor? fine: lay out a huge amount of stuff"

"No, I need it more accurate! fine: lay out tracks, now burn fuses to select
from unit-scale tracks the 'right' number, and if you want better _use a
laser_ to do it"

~~~
dfox
The general rule for precision electronics is that you want to avoid anything
that needs high absolute accuracy (because such things get expensive fast even
as discrete components) and instead rely on accurate ratios between
parameters, matched pairs of components and inaccurate, but long term stable
parameters that can be calibrated out.

~~~
JadeNB
> The general rule for precision electronics is that you want to avoid
> anything that needs high absolute accuracy (because such things get
> expensive fast even as discrete components) and instead rely on accurate
> ratios between parameters, matched pairs of components and inaccurate, but
> long term stable parameters that can be calibrated out.

The omitted serial comma made that really hard to parse for me. In case it did
for anyone else, I think that it's:

> (accurate ratios between parameters) and (matched pairs of components) and
> (inaccurate, but long-term stable, parameters that can be calibrated out).

~~~
acomar
I've started using hyphens to offset clauses that nest inside of other comma-
separated syntactic structures for this reason. It keeps my intent way more
clear without forcing the reader to reparse the sentence if they incorrectly
guess how the commas are supposed to line up.

> accurate ratios between parameters, and matched pairs of components, and
> inaccurate - but long-term stable - parameters that can be calibrated out.

is much easier to follow at a glance.

~~~
dfox
That is what I wanted to rewrite it to, but it is too late to edit the comment
;)

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rkagerer
The link on forming capacitors leads to a rather interesting old book on IC
fabrication, which is still relevant for fundamentals (you can scroll up for
other devices):

[http://books.google.com/books?id=aByz--
9D63wC&lpg=PA31&ots=Z...](http://books.google.com/books?id=aByz--
9D63wC&lpg=PA31&ots=ZJ3V72sLcD&dq=%22junction%20capacitor%22%20integrated%20circuit&pg=PA31#v=onepage&q&f=false)

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ardy42
> The MagSafe adapter and other laptop adapters use it, as well as
> minicomputers, LEDdrivers, audio power supplies, video games and
> televisions.[4]

The word minicomputers is a dead link to
[https://web.archive.org/web/20170118103738/http://bitsavers....](https://web.archive.org/web/20170118103738/http://bitsavers.informatik.uni-
stuttgart.de/pdf/hp/1000/A-series/02156-90003_A600_A600+_ERD_Vol2_Jun84.pdf),
which is some reference documentation for the HP 1000 A600 computer.

~~~
kens
Thanks, I've fixed the link.

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yjftsjthsd-h
Looks like (2014).

Nice explanation. Always fun to see the actual intersection where physical
properties create a functional circuit.

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kens
Any other suggestions for common yet generally unknown chips?

~~~
jakehop
The NE555-timer is quite a cool little thing.

More common operational amplifiers are also worth looking into (TL072 is one
of my favorites).

Lastly, the 7400-series logic chips are SO interesting. If you need the
programmer's version of a jigsaw puzzle, try to build somewhat advanced
designs using those. It's very fun and a good learning experience (although
hard!).

This guy is building a computer on a breadboard – very intersting indeed:
[https://www.youtube.com/channel/UCS0N5baNlQWJCUrhCEo8WlA](https://www.youtube.com/channel/UCS0N5baNlQWJCUrhCEo8WlA)

~~~
segfaultbuserr
NE555 is not "unknown" (most popular chip in the entire history of electronic
engineering), 74xx and TL072 are not unknown either, anyone who knows a little
bit of hardware knows the chip.

TL431 is popular yet unknown to most people outside the world of switched-mode
power supply. I think the OP wants some popular yet relatively less-known chip
to those who is outside of the field.

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olliej
This was really interesting, but also it just as a byproduct of the
explanation actually explains how the core circuit elements are actually
implemented (resistors, NPN vs. PNP transistors) which I found really
interesting. I had a general idea of transistor implementation, but always
just assumed resistors were varying dopants or some such, rather than the now
obvious "make it longer/thinner".

~~~
marcosdumay
As a rule, you want your resistors made of metal. Semiconductor resistors have
a lot of really surprising behavior.

But, yeah, if precision and stability do not matter, it's cheaper to make them
out of silicon.

~~~
SAI_Peregrinus
> As a rule, you want your resistors made of metal. Semiconductor resistors
> have a lot of really surprising behavior.

So much so that probably the most common semiconductor resistors where
linearity is needed are actually transistors. Stick on external reference
resistor in, use current mirrors inside to distribute the reference current
around the circuit, and use transistors in the active region (linear region
for FETs). It's also cheaper since transistors take less area than resistors.

~~~
olliej
Follow up dumb question - I thought transistors take time to
charge/discharge/do-physics-things, how do they avoid resistance changing over
time.

~~~
SAI_Peregrinus
They change a bit, but primarily at startup. After that they're controlled by
the stability of the biasing.

I'd recommend "Designing Analog Chips" by Hans Camenzind[0], the designer of
the 555 timer. Particularly chapter 3, "Current Mirrors".

[0]
[http://www.designinganalogchips.com/](http://www.designinganalogchips.com/)
has a free pdf

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psim1
I am pleased that part of his reverse-engineering process included smashing
open the package using a vice-grips as this is the kind of barbaric method I
would use. I feel more connected to the article in this way.

