74ac02 unused input pins

tonitze · 20th April 2005, 02:19 PM

Is it advisable to ground all unused input pins of the 74ac02?
Please advice.

Toni.

macboy · 20th April 2005, 03:03 PM

Yes, but keep in mind that with both inputs grounded, the output will be high. Ground that, and you are asking for trouble. Generally, you can ground all unused inputs; leave unused outputs unconnected. Some logic types may have pull-up resistors on the inputs (or even the outputs) which is a consideration when determining whether you want to pull-up or pull-down the unused inputs. With AC series though, you should be fine either way.

Jocko Homo · 20th April 2005, 03:52 PM

You would be better off avoiding AC logic. HC logic should be good enough; if not try VHC. Most anything but AC.

Jocko

tonitze · 20th April 2005, 04:13 PM

Thanks Jocko and Macboy. I will try out the VHC on my next clock circuit.

Toni.

Guido Tent · 20th April 2005, 07:30 PM

Quote:

Originally posted by tonitze
Thanks Jocko and Macboy. I will try out the VHC on my next clock circuit.

Toni.

Hi

Firts follow Jocko's advise. Then connect all unused inputs to Vcc and ground all unused outputs. After you've done that figure out why.

cheers,
-

seoman · 20th April 2005, 09:09 PM

Ground all outputs

Ok I dig the part of connecting to VCC.
Aspecialy the old TTL ports use less power that way.
But i would never ever connect an output to a power line.
That's asking for smoke!

PLease explain

Simon

Guido Tent · 20th April 2005, 09:35 PM

Quote:

Originally posted by seoman
Ground all outputs

Ok I dig the part of connecting to VCC.
Aspecialy the old TTL ports use less power that way.
But i would never ever connect an output to a power line.
That's asking for smoke!

PLease explain

Simon

Hi

The goal is lower inductance and damping in the ground circuit (off chip - on chip).

Why the smoke ?

cheers

seoman · 21st April 2005, 07:18 AM

Well
If you make a mistake the chip will draw a lot of current from the supply.

Ok some people won't make a mistake but......
People reading this posts could think they always should do this trick.
And thats tricky!

Regards Simon

tonitze · 21st April 2005, 12:03 PM

Today just follow Guido's advice by connecting unused inputs to vcc and outputs to gnd. No smoke at all and the 74hcu04 runs at normal temperature. Improvement, wasn't sure but somehow sound smoother. Lower noise I guess.

Toni.

BrianL · 21st April 2005, 01:52 PM

Guido, et al., I agree with seoman

I really question the suggestion to ground the unused
outputs.

It's always good practice to pull up all unused
inputs (with resistor, such as 1K unless the input is in
a gate you're using which might require pulling low)

If the unused output is naturally going low as a result
of your input setting, you still have the potential for
pulling current through the output and I don't see
that as a good or safe thing. I can't see how
connecting the output to ground will have any
salutary effect as the only think it can do is
cause more currents (hopefully DC) to circulate.

I also agree with Jocko to avoid AC logic (and "FACT' as well)

20th April 2005, 02:19 PM	#1
tonitze diyAudio Member Join Date: Feb 2003 Location: singapore	74ac02 unused input pins Is it advisable to ground all unused input pins of the 74ac02? Please advice. Toni.

20th April 2005, 03:52 PM	#3
Jocko Homo Banned Join Date: Feb 2002 Location: As far from the NOSsers as possible	Yes, but........... You would be better off avoiding AC logic. HC logic should be good enough; if not try VHC. Most anything but AC. Jocko

21st April 2005, 01:52 PM	#10
BrianL diyAudio Member Join Date: Mar 2002 Location: USA	Guido, et al., I agree with seoman I really question the suggestion to ground the unused outputs. It's always good practice to pull up all unused inputs (with resistor, such as 1K unless the input is in a gate you're using which might require pulling low) If the unused output is naturally going low as a result of your input setting, you still have the potential for pulling current through the output and I don't see that as a good or safe thing. I can't see how connecting the output to ground will have any salutary effect as the only think it can do is cause more currents (hopefully DC) to circulate. I also agree with Jocko to avoid AC logic (and "FACT' as well) __________________ bel

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20th April 2005, 03:03 PM	#2
macboy diyAudio Member Join Date: Oct 2003 Location: Ottawa, Canada	Yes, but keep in mind that with both inputs grounded, the output will be high. Ground that, and you are asking for trouble. Generally, you can ground all unused inputs; leave unused outputs unconnected. Some logic types may have pull-up resistors on the inputs (or even the outputs) which is a consideration when determining whether you want to pull-up or pull-down the unused inputs. With AC series though, you should be fine either way.

20th April 2005, 04:13 PM	#4
tonitze diyAudio Member Join Date: Feb 2003 Location: singapore	Thanks Jocko and Macboy. I will try out the VHC on my next clock circuit. Toni.

20th April 2005, 09:09 PM	#6
seoman diyAudio Member Join Date: Apr 2004 Location: Nijmegen	Ground all outputs Ok I dig the part of connecting to VCC. Aspecialy the old TTL ports use less power that way. But i would never ever connect an output to a power line. That's asking for smoke! PLease explain Simon

21st April 2005, 07:18 AM	#8
seoman diyAudio Member Join Date: Apr 2004 Location: Nijmegen	Well If you make a mistake the chip will draw a lot of current from the supply. Ok some people won't make a mistake but...... People reading this posts could think they always should do this trick. And thats tricky! Regards Simon

21st April 2005, 12:03 PM	#9
tonitze diyAudio Member Join Date: Feb 2003 Location: singapore	Today just follow Guido's advice by connecting unused inputs to vcc and outputs to gnd. No smoke at all and the 74hcu04 runs at normal temperature. Improvement, wasn't sure but somehow sound smoother. Lower noise I guess. Toni.

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