Hey folks, Crow here. One of the great boondoggles of product design is getting everything working just right and then receiving the dreaded “part life status notification” email from a supplier or vendor. Consider the following example: in 2013 while working out the design for the voice board for my crOwBX project (see http://www.cs80.com/crowbx/ ) I selected the Linear Systems LS318P in the DIP8 package for use as the exponential multiplier matched transistor pair for each oscillator as that part is vastly superior to the venerable LM3046. Rev.1 prototype and rev.2 production boards used the LS318 DIP part. Linear Systems offered the device in DIP8, SOIC8, and TO78 (metal can) packaging. Later that year I get a part status notification that the DIP8 package was to be discontinued. No DIP package but the metal can was still available? There must be a lot of legacy radar systems that need such a part was all I could think of. Not wanting to get stuck with a package end-of-life issue again, I changed the board layout from the first image to the second.
The idea here is to not get caught in a packaging bind again as this configuration provides DIP pads, SOIC pads, two options for mounting the temperature compensation resistor R28, and extra pads to even allow the T-package to fit. In addition a pair of hand-matched discrete transistors can be used or other monolithic devices that share the pinout such as the SSM2210 (which is also EOL’d btw). This way the design has a measure of built-in anti-obsolescence. Below is a comparison of a rev. 1 and a rev. 2.2 voice board illustrating the new configurations. Cheers!
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