74hc04 datasheet

Normally 3V is OK for HC series.

Jim Thompson wrote: ...

...

Most of the manufacturers specify the additional power consumption for an HCT04 due to an input being at 2.4V rather than VCC/gnd - usually about 3mA max although Philips specs about 1/2 mA.

Interestingly the schmitt trigger HCT14 has a similar specification - I wondered if the feedback would encompass the input stage but apparently not.

kevin

I won't speak for that spec sheet, as described, it sounds like an error someplace. But I will address your comment about input-stage rail-rail currents. Yes, 74HCT 5V logic with 3.3V inputs may draw extra input-stage supply current, but it won't be much, given that a) the input level is well past the threshold, and b) the device's input stage is made from small-geometry FETs, as you know very well. While it's very attractive to use 74LVC, etc., with 3.3V supplies, etc., in new designs (I do like it), millions of older designs are doing quite well with their old 74HCT 5V logic, dealing with 3.3V inputs. So, I'd say, no need to cast any undue aspersions on them.

They can be faster, that's one serious advantage.

--
 Thanks,
    - Win

It means that you must give it 3.15V with a 4.5V power supply to guarantee a "1". You can assume that it will be even higher with a 5.5 or 5.25V power supply. It typically will require only 2.4V (again with the 4.5V power supply). It won't work reliably with a 5.0V nominal power supply and a 3.3V nominal input.

If you use a 74HCT04, it only requires 2.0V guaranteed for Vcc 4.5 to

5.5V (typical 1.6V) which should be fine for your application.

Best regards, Spehro Pefhany

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Hi,

I want to drive a 74hc04 running on a 5V supply with a 3.3V signal. But looking at the datasheet I'm not sure if this is OK or not. At Vcc=4.5V, it gives a Vih(min) of 3.15V. However, it also says that Vih(typ) is 2.4V.

How can the typical Vih be lower than the minimum Vih? Can anyone give me any hints about what the datasheet is trying to tell me here?

Steve

I have used TI's SN74LVC4245A chips with great sucess for this purpose. I also like the fact that they are dirt cheap. You may also want to look for logic that is in the LV family, such as a 74LV04. The LV, which I am guessing stands for low voltage, tends to be much more 3.3V compliant.

No aspersions, just an observation. Many of us chip designers fret over even minute power. I have an RFQ on my desk for a chip drawing a total VDD current of 1uA :-(

My first 3.3V to 5V translator design was done in 1996 for Intel's USB receiver.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

I recently worked on a hearing aid design that had a MEMS microphone on-chip.

On my website is a schematic of a hearing aid with sliding-class-A output stage bias... current goes way down when all is quiet.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Hello Jim,

Sounds cool. Don't we all love challenges? I wonder why hearing aids (the plain and simple ones) aren't smart enough to do that. AFAIK it's all on a chip in there. People have to either open the battery lid or take out the batteries to fully turn them off. I wonder why they couldn't figure out how to make them drop to a few uA when the volume is turned fully down. Especially considering that most users have to look for their glasses before removing the battery for the night.

Regards, Joerg

Hello,

Dirt cheap? At 35c? The HCT04 is 8c or less.

Regards, Joerg

No. Even at 4.5V VCC the data sheet says that the input must be 3.15V at minimum for a high level. Else it may go into pseudo-analog behavior which Steve certainly doesn't want.

Regards, Joerg

There's a 0.3mA (max) *per input* adder in there, depending on input level..

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

That is an interesting concept. 700uA can still be a bit high though, considering the small mAh rating of hearing aid batteries. A sliding class-A also won't help too much if people take out their hearing aids and put them on the night stand. There can still be lots of noises to make it kick in. Rain hammering on the roof/window, the tick-tock of the old alarm clock or a snoring person. The loudest snorer in our house is our rottie mix. He sounds like uncle Leroy's wood shop.

Then there is the unhealthy habit of some people using the TV as a sleeping aid. Our of my neighbors in my college days used to do that and she had to turn the volume to full blast to hear some of it without her hearing aid. Often it kept droning on all night until the first "nature call".

This is the trick they use on VHF radios a lot: The whole radio powers off. Decoupling capacitances are painstakingly minimized. Then the radio turns itself on for short regular bursts and goes off if no signal is detected. If a signal is there it stays on but only until shortly after the end of that transmission. If it is designed right you don't even know that the radio does this.

Regards, Joerg

"Steve" schreef in bericht news: snipped-for-privacy@x2.org.uk...

Steve,

That 3.15V is a well known figure seen in most if not all HC datasheets. So if the driving voltage is 3.3V you're within the margins although pretty close to the edge. An old trick is using a pullup resistor to +5V but you should first make sure that the output of the 3.3V logic can stand it. If it's open collector/drain I'm almost sure it will.

BTW What datasheet are you reading? Can't find that Vih(typ) in mine.

petrus bitbyter

"Jim Thompson" schrieb im Newsbeitrag news: snipped-for-privacy@4ax.com...

TI 74CB3T3245 needs 40uA for 8 level shifters (bus switches), not bad. I measured about 10uA at room temperature. But it's dirt expensive.

see:

The 74CB3T3306 ("USB version") costs exactly the same:

but has 20uA ICC worst case only.

MIKE

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Michael Randelzhofer
FPGA und CPLD Mini Module
Klein aber oho !

If you are really using a 5V supply then change the chip to a 74HCT04. The HCT series have a lower input threshold, but are only able to run from 5V supplies, not 2V to 6V. The output levels will be the same whichever you choose.

Chris

I think the LV doesn't like 5V

--
Vih(min) is the lowest (the minimum) input voltage which is
guaranteed to drive the output of the gate low.  Typically, 2.4V
will do it, but if you want a guarantee, make sure that Voh(min) of
the driving stage is guaranteed to be >= 3.15V.

Hello John,

3.15V is for a VCC of 4.5V. If VCC is 5V it'll be more like 3.5V or a bit higher than that if allowed to tolerance up to 5.25V. It seems that the factor in the data sheet between VCC and guaranteed threshold for input high is 0.7.

Regards, Joerg