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TTL input Voltage compatibility problem

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francis29

francis29

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I am using SN74AHC244MPWREP as TTL input buffer . VCC is connected to 3.3 Volts. Is it okey if i connect 5V TTL signal to this chip?
Does it work perfectly like 3.3V TTL?
 

74AHC is 5V input tolerant and can be used for 5V to 3.3V translation. For better performance you might prefer a 3.3V series with 5V input tolerance like 74LVC.
 
Hi,

Every datasheet answers the initial question.

Here: absolut max input voltage range:
* Non 5V input tolerant devices say something like " VCC + 0.5V". This means input voltage on a 3.3V supplied device must not be higher than 3.3V + 0.5V = 3.8V. --> The signal input voltage range depends on VCC.
* 5V input tolerant devices say something like: "6.0V". This independent of VCC.

Some 5V input tolerant devices even specify the signal input current when device is not powered--> VCC = 0V.

Klaus
 
Datasheet says maximum of 7 Volts for input in absolute maximum rating section.
 

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