How to check buffer/Driver is BAD or Data is not passing through

[justin126912]

Hi All,

I have the following Buffer IC from TI 74LV244 below. How do I check whether the chip bad or damaged or data is not passing through? Any help direction would be greatly appreciated

 

[Pommie]

Aren't A the inputs and Y the outputs? Or are your arrows the wrong way?

Mike.

 

[justin126912]

Hi Mike,

Thanks for the reply. Do you think I could use the changing signals as Vcc and GND as input and check the outputs?


Thanks,

WJ

 

[Pommie]

That is what you would normally do (via a resistor) but you appear to have inputs and outputs swapped.

Mike.

 

[justin126912]

Hi Mike,


This is what I was hoping to do, Would this be a problem? any additional ideas would be greatly appreciated



**broken link removed**

 

[Pommie]

That should work as long as you ground the enable pins.

Mike.
Edit, what are you using this for?

 

[rjenkinsgb]

1V input swing is not enough to give reliable operation at 3V.

The 74LV244 data states a maximum low input of 0.8V and a minimum high level of 2V (same as 5V TTL logic levels) when operating on or around 3.3V supply, so a minimum signal swing of 1.2V, IF it's perfectly biased to the appropriate range centred exactly on 2.4V
Too low or too high with such a small swing will give erratic operation, if anything.

For reliable operation and noise immunity, the input swing should ideally be from near 0V to something greater than 2.5V
The '244 inputs are schmitt triggers (at least on the bipolar versions; it's not clear on CMOS ones) so have hysteresis by design to prevent false switching.

The output swing will be near equal to the supply voltage, as long as the load is not excessive.

https://assets.nexperia.com/documents/data-sheet/74LV244.pdf

(A 74LS244 as in the last post in only specified for around 4.5-5.5V supply; with a 5V supply it would work with 3.3V logic level inputs).

 

[Pommie]

1V input swing is not enough to give reliable operation at 3V.

Didn't spot that and assumed connection to Vcc and Gnd as in his previous post.

Mike.