74HC vs.74AHC Logic Gates - Page 1
Forum section: electronics / beginners

author: Falcon69
author_rank: Super Contributor
timestamp: September 29, 2016, 04:17:26 am
content: Hey Guys.I'm redesigning my circuit. I've noticed that the 74HC86 XOR Gate is not offered in a SOT-762 (DHQFN14) package, and is only offered in the SOT-402 (TSSOP-14).http://www.nxp.com/documents/data_sheet/74HC_HCT86.pdfNow all the Logic Gates I am using are all HC versions, and the circuit works just great!However, I'm redesigning to make the board smaller and with more features, so it will call for the SOT-762 packages. I've noticed they make a 74AHC86 chip in that Package size. It seems to be the automotive version of the 74HC86.http://www.nxp.com/documents/data_sheet/74AHC_AHCT86_Q100.pdfI've tried to understand the data sheet. It seems it could be twice the speed? Since my circuit only handles a few Hall Effect Sensors and LED's....Speed isn't really an issue (except I have been told the LVC chips are just way to fast for my application, although those worked just fine also it seemed when i used them before). So, can I substitute the chip with the automotive version?Thanks in advance,J

author: wraper
author_rank: Unknown
timestamp: September 29, 2016, 04:45:42 am
content: Quote from: Falcon69 on September 29, 2016, 04:17:26 amHas nothing to do with automotive and is not a version of HC. Just different/newer series. You can read the same automotive thing for HC series toohttp://www.nxp.com/documents/data_sheet/74HC_HCT86_Q100.pdf

author: wraper
author_rank: Unknown
timestamp: September 29, 2016, 04:47:14 am
content: http://www.ti.com/lit/an/scaa034c/scaa034c.pdfQuote

author: Falcon69
author_rank: Super Contributor
timestamp: September 29, 2016, 04:49:38 am
content: oh, you are right. I had misread the Data Sheet. the Q100 listed at the end of the part numbers tell you it complies with the AEC standard Q100 and is suitable for automotive application.I understand now. The AHC is a different series than the HC, therefore, that explains why the different speed rating.

author: Zero999
author_rank: Super Contributor
timestamp: September 29, 2016, 07:59:09 am
content: How many logic gates do you have?If it needs to be smaller then how about replacing the logic gates with a programmable device such as a CPLD or MCU?

author: Kleinstein
author_rank: Super Contributor
timestamp: September 29, 2016, 04:52:51 pm
content: There are also so called "single gate" series - so smaller chips, but less functions. This could be interesting if only one gate is needed.

author: Falcon69
author_rank: Super Contributor
timestamp: September 29, 2016, 04:56:20 pm
content: in the whole circuit? A mix of 72 Logic Gates, 1-8input NAND, and 10 inverters. I thought about a programming device, but by the time I add all the tansistors/mosfets needed to drive what the logic gates do, then I'm at the same or higher footprint size of the PCB Board. The Logic gates, most of them, are sinking and powering an LED so a transistor isn't needed.I was just hoping to keep all my Logic Gates the same package size. But that XOR gate is the only one that doesn't come in the SOT-762 (DHQFN14). I wonder if I could just change them all from CH to the AHC series and be okay.?

author: Falcon69
author_rank: Super Contributor
timestamp: September 29, 2016, 04:58:00 pm
content: Quote from: Kleinstein on September 29, 2016, 04:52:51 pmYes, but, there are 10 individual circuits, of which each can share the same chip if it has 4 gates inside, making the pcb board size smaller. So I'd rather stick with a 4-gate chip.