Electronics > Projects, Designs, and Technical Stuff
LM399 - die analysis
Noopy:
--- Quote from: Noopy on January 18, 2020, 12:10:50 pm ---I´ll try to take a better shot of the area… :-/O
--- End quote ---
No, I don´t think that´s a Transistor...
Wimberleytech:
--- Quote from: Noopy on January 18, 2020, 05:00:02 pm ---
--- Quote from: Noopy on January 18, 2020, 12:10:50 pm ---I´ll try to take a better shot of the area… :-/O
--- End quote ---
No, I don´t think that´s a Transistor...
--- End quote ---
Looks like a resistor to me
Noopy:
Hi all!
Thanks to imo I was able to take some pictures of a MAC199:
https://www.richis-lab.de/REF02a.htm
The structures are very similar but not exactly the same.
Tesla had to do quite some mask revisions.
In my view like in the LM399 there is no second additional transistor as described in the tesla datasheet.
The schematic looks like this:
The grey line is disconnected in the MAC199. So whatever the lower transistor compensated it´s not functional in the MAC199.
Another interesting point is the die attach. The die is not directly bonded to the package. It sits on top of something which looks like a thinner die:
...the LM399 has the same "double-die"...
:popcorn:
Cerebus:
I can't find anything specific to the LM199/299/399 but it's not uncommon for voltage reference chips to have unconventional die attachments. Differential temperature related movement of the case and die, owing to the different temperate coefficients of expansion of the disparate materials, induces varying strains in the substrate causing drift. So some kind of 'floating' or compliant attachment makes sense for high precision references.
Noopy:
Do you remember me saying that in the LM399 there is a additional circuit similar that shown in the datasheet of the MAC199?
I claimed one of the two additional transistors isn´t actually there. I was pretty sure that it´s a resistor:
Well some days later: It could be a transistor!
Probably the brown "resistors" are p-doped. If there is an additional n-doped area under the upper contact than we have a pn-structure. With the n-doped well you get an npn-transistor.
Fine! :-+
If you don´t want that every structure in the well interacts with the half transistor the well has to be more positive than everything else. The most positive potential is the red one coming from left into the picture. But it seem´s that the well is connected to the second yellow contact of the resistor. Since the role of the transistor is a shorting of the resistor it´s ok to connect the well to the second highest potential, the second contact of the resistor.
Fine! :-+
It´s more a parasitic transistor and possibly not a very good one but it should work.
:-/O :popcorn:
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