Screaming Circuits: It Lives!


It Lives!

I think the very first logic gate I got my hands on was the 7408 quad AND gate. Not a 74AC or HCT or anything like that. Just plain old SN7408N - probably made by Texas Instruments. The first actual gate I played with would have been an inverter, but that was a proto board wired single transistor job made with a 2N2222.

7400_2 Yes, the first IC logic gate was the 7408. Well, the first of the 7400 series was actually the 7400 quad NAND gate, but the first one I used was the AND gate. I'm not going to tell you how many million years ago that was, but it was a few.

If you're a regular reader of this blog, you are undoubtedly somewhat familiar with the QFN (Quad Flat pack No lead) package. We see many of the newest components coming out in this package. It has better thermal characteristics than other packages and is a lot smaller. Since much of the really high volume is with cell phones and other hand held devices, "small" is where the volumes and profits are for chip makers. These days it is not uncommon to see chips only come out in a QFN package or at least launch with that package and add larger packages later.

I just read an article in Planet Analog article about Texas Instruments releasing new versions of 7400 series logic in QFN packaging (TI calls it an RGY package). My SN74LVC08A is still a 14 pin device with the exact same pin-out as the original 7408. It's 3.5 x 3.5mm and 1mm thick. Costs $0.50 each in quantity one at Digi-Key.

Every now and then, I'll need a basic logic gate for some robot or motor driver I'm building up. I still have an old proto board and a few of the old '70s vintage chips and they still work. Like you, though, if I wanted to use the new QFN version, I'd have to run it through Screaming Circuits. No hand soldering there.

Duane Benson
Long live the 7400!


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