[sdiy] Odp: Resistor Networks....

Roman modular at go2.pl
Sun Aug 30 11:22:58 CEST 2020


Resistor networks are mostly used for multiple signal lines needing them, like in dense digital design. At this price level, the assembly cost more than the part, so it's a huge difference if only one component needs to be placed instead of 4 and sometimes even 8.  There are indeed precision resistor networks available and they really can have impressive tolerances, usually matching to each other better than absolute resistance. Sometimes in a form of 2-resistor divider designed for gain settings, made with insane precision (and price). And they are better thermally coupled than any separate resistors. But do you really need 0.01% there? Or excellent temperature matching?   I have used several reels of resistor networks so far, and even though I hate them, the 4x reduction it placement is so attractive that I still use them in new designs.  Why they are bad? The distances between terminals are sooo tiny, you would never place any 2 componets so close on purpose. Think about tin whiskers, or errors in assembly. On numerous times I could find super thin hair shorts between pads only during final electric test. No matter if it's hand soldered or reflow.   Also, there's much greater variety of single resistors than networks available. And they are cheaper. Not to mention flexibility in PCB routing.   Roman  yes, I'm still alive  Dnia 30 sierpnia 2020 05:35 Pete Hartman <pete.hartman at gmail.com> napisał(a):  I'm working on laying out a classic through hole module design with SMD parts.  The original uses a fair number of resistor networks, most of them just parallel resistors, not common bus versions.  The resistor networks are, well... huge by comparison.   Unfortunately the original designer isn't around for me to ask for input.   My *impression* based on how the networks are being used (often times for things like input resistors and a feedback resistor in a summing op amp config, just as one example) is that part of their purpose was to get parts that were well matched.  But that's not anything but a gut feeling.   So I'm looking for seasoned opinions about whether there is any important reason to keep resistor networks, when I can sub in 1% SMD parts that will take up less space and be more flexible for placement.  Are the networks either 1) better matched even than 1% parts, or 2) have some other characteristic which I'm not thinking of that might be important?   Thanks   Pete  ______________________________  Synth-diy mailing list   Synth-diy at synth-diy.org  synth-diy.org synth-diy.org
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