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| Replace HC by HCT, and LS by HCT |
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| luiHS:
Hello. I have a circuit that uses 7407 and 74HC374, in addition to other 74xx chips. The problem is that I want them in TSSOP format on a reel with 12mm wide tape for my Pick and Place Neoden4. Those two chips in particular I've only found them on 16mm tape. Looking for the 74HCT374 to find that it is on TSSOP 12mm tape, and I thought that I could replace the 7407 with a 74HC4050 that is also available on TSSOP 12mm wide tape. Can they be replaced without problems? On the other hand I have another circuit that uses 74LS chips, all of them only on 16mm tapes, even one on 24mm tape. Could I replace the 74LS by 74HCT? These I have found in TSSOP 12mm of tape width, I think that all 74LS can be replaced by 74HCT but I am not 100% sure. Regards |
| wraper:
LS can be replaced with HCT. That's the main reason HCT exists to begin with. However they have weaker output capability than LS and especially compared with plain 7400 series. Thus if you try to drive multiple 7400 inputs or too many LS inputs with 74HCT/HC, you likely will have an issue. When using HC series instead of TTL you need to take care if logic high on the inputs have enough voltage. https://www.onsemi.com/pub/Collateral/AN-368.pdf.pdf |
| wraper:
Also if circuit is poorly designed and depends on propagation delay a lot, you may have issues as well. |
| luiHS:
Thanks. Do you know if can I replace HC by HCT ? |
| wraper:
--- Quote from: luiHS on May 23, 2019, 08:41:59 pm --- Thanks. Do you know if can I replace HC by HCT ? --- End quote --- You usually can do this just fine. The downside would be reduced noise immunity due to lower logic high level. However I would expect the same packaging options available as long as HC/HCT come from the same manufacturer. |
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