
Tiny transformer inside: Decapping an isolated power transfer chip - sohkamyung
http://www.righto.com/2020/05/tiny-transformer-inside-decapping.html
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kens
Author here: I'm sure there are people on HN who have experience with modern
chip layout, and I'd be thrilled if you can explain more about the transistor
structures and so forth. I mostly look at chips from the 1970s and 80s, and a
lot has changed since then :-)

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cushychicken
That tiny little heatsink is very cool. (Pun not intended.)

Do you happen to have a post about the setup you use to photograph these die,
Ken? I'd love to get my hands on something similar.

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kens
I have a post about my setup [1]. The main secret is a metallurgical
microscope: unlike most microscopes, this shines light from above, through the
lens, so you get good illumination of the die. (A ring light is easier, but it
doesn't help at high magnification. Also, light from the side doesn't work as
well.) I use a low-end metallurgical microscope that I found on eBay. You can
see interesting stuff with a regular microscope, so take a look at chips if
you have one, but a metallurgical microscope makes a huge difference.

For the die photos, I stitch together multiple photos using the "Hugin"
software package. I might use a dozen to 50 individual photos to produce a
high-resolution image. Hugin has a learning curve, though.

The final thing is how to decap the chip. Usually, I stick to ceramic or metal
packages that I can open with a chisel or hacksaw. For epoxy packages, I don't
want to mess around with boiling acids, but I have friends who can do this.

[1] [http://www.righto.com/2015/12/creating-high-resolution-
integ...](http://www.righto.com/2015/12/creating-high-resolution-
integrated.html)

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cushychicken
Awesome! I'll check that out.

Can't blame you for not wanting to handle boiling acid. Ain't nobody got time
for that. (Except for your friends, and ZeptoBars.)

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willis936
It’s always worth it to read through the footnotes. I got a kick out of
imagining this. If it were me, there would have been loud profantiy.

“6. I accidentally dropped the primary die down the drain while trying to
clean it, so I don't have many pictures of the primary die.”

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lxe
I love this sort of stuff on HN: seems pretty complicated at first, but the
author dived deep into the meat of how it works while making each step
extremely easy to understand.

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Renaud
These tiny isolated DC to DC converters are amazing.

When you think that they can withstand kV, some for minutes at a time, it's
pretty impressive engineering, all in a tiny form-factor that still manages to
be highly efficient and avoid over-heating.

I'm amazed by the knowledge that goes into making these, all the various
disciplines that need to work together to make these tiny devices...

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wolf550e
What does the logic implemented using standard cell circuitry do in this
design? I thought this is a "dumb" component, no calculations inside?

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kens
My guess is it's a mixture of analog and digital stuff. On the analog side,
there's probably a bandgap voltage reference, temperature and current sensing,
soft-start circuitry. It needs to detect the primary's clock and lock on it
(probably with a PLL), and adjust the phase as necessary. Then there will be
drivers for the power transistors.

The digital side is probably fairly simple logic to stop the chip if there's a
fault and restart it if the fault goes away. From the datasheet, there are
various different overload states it can go into, limiting power, changing to
passive rectification, and then shutting down entirely. So the logic would
need to manage these states.

There's always the possibility that they threw a microcontroller in to handle
this, but it seems like overkill. Also, I didn't see anything that looked like
ROM. So I think the control is hard-wired.

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zapdrive
Best "hacky" article on Hacker News in the recent history.

