Author Topic: 74HC vs.74AHC Logic Gates  (Read 3414 times)

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Offline Falcon69

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74HC vs.74AHC Logic Gates
« on: September 29, 2016, 02:17:26 pm »
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.pdf

Now 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.pdf

I'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
« Last Edit: September 29, 2016, 02:25:25 pm by Falcon69 »
 

Offline wraper

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Re: 74HC vs.74AHC Logic Gates
« Reply #1 on: September 29, 2016, 02:45:42 pm »
It seems to be the automotive version of the 74HC86.
Has 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 too http://www.nxp.com/documents/data_sheet/74HC_HCT86_Q100.pdf
« Last Edit: September 29, 2016, 02:49:58 pm by wraper »
 

Offline wraper

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Re: 74HC vs.74AHC Logic Gates
« Reply #2 on: September 29, 2016, 02:47:14 pm »
http://www.ti.com/lit/an/scaa034c/scaa034c.pdf
Quote
Advanced High-Speed CMOS (AHC)
AHC can be used for higher-speed applications. Some advantages of using AHC over HC are:
• The AHC logic family is almost three times faster than the HC family. The AHC logic family has a typical
propagation delay of about 5.2 ns.
• The AHC logic family allows designers to combine the low-noise characteristics of HCMOS devices with today’s
performance levels without the overshoot/undershoot problems typical of higher-drive devices.
• The AHC family has lower power consumption than the HC family.
• The output drive is ±8 mA at 5-V VCC and ±4 mA at 3.3-V VCC.
• AHC devices are available in D and DW (SOIC), DB (SSOP), N (PDIP), PW (TSSOP), and DGV (TVSOP)
packages. Selected AHC devices are available in military versions (SN54AHCxx)
 

Offline Falcon69

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Re: 74HC vs.74AHC Logic Gates
« Reply #3 on: September 29, 2016, 02:49:38 pm »
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.
 

Offline Zero999

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Re: 74HC vs.74AHC Logic Gates
« Reply #4 on: September 29, 2016, 05:59:09 pm »
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?
 

Offline Kleinstein

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Re: 74HC vs.74AHC Logic Gates
« Reply #5 on: September 30, 2016, 02:52:51 am »
There are also so called "single gate" series - so smaller chips, but less functions. This could be interesting if only one gate is needed.
 

Offline Falcon69

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Re: 74HC vs.74AHC Logic Gates
« Reply #6 on: September 30, 2016, 02:56:20 am »
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.?
 

Offline Falcon69

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Re: 74HC vs.74AHC Logic Gates
« Reply #7 on: September 30, 2016, 02:58:00 am »
There are also so called "single gate" series - so smaller chips, but less functions. This could be interesting if only one gate is needed.

Yes, 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.
 


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