74hc04 datasheet
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Posted by Steve on October 27, 2005, 2:05 am
Please log in for more thread options 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 | ||||||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by eeh on October 26, 2005, 7:50 pm
Please log in for more thread options Normally 3V is OK for HC series. | ||||||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by Joerg on October 27, 2005, 7:30 pm
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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 http://www.analogconsultants.com | ||||||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by Spehro Pefhany on October 26, 2005, 9:27 pm
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On Thu, 27 Oct 2005 02:05:56 +0100, the renowned Steve >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 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 -- "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 | ||||||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by Jim Thompson on October 26, 2005, 6:41 pm
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On Wed, 26 Oct 2005 21:27:44 -0400, Spehro Pefhany >On Thu, 27 Oct 2005 02:05:56 +0100, the renowned Steve
> >>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 >
>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 None of this is very savory. It is likely that the input stage will draw some overlap current, if the input doesn't go all the way to VDD. I'd look for chips that do 3.3V to 5V translations and vice versa. ...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. | ||||||||||||||||||||||||||||||||||||||||||||||||||||
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