SN74LVC1G240: SN74LVC1G240

Hi Glenn and welcome to the forums,

It seems you have a lot of questions similar to ones that I had the first time I saw a logic datasheet.  I will try to address each in order.

The data  sheets indicate a minimum value of resistance to connect OE to VCC. But there is no

information on how to calculate this. So where is the formula?

I think you're talking about page 1 of the datasheet where it says "To ensure the high-impedance state during power up or power down, OE\ should be tied to Vcc through a pullup resistor; the minimum value of the resistor is determined by the current-sinking capability of the driver."

This statement is specifically referring to the situation in which you have a controller connected to the OE\ pin, but also want to ensure that the device remains in high impedance mode prior to the controller turning on. A weak pull-up resistor is typically used (4.7kohm, 10kohm, and 100kohm are all common values) to hold the pin high until the controller is active.

Once the controller is on, it will drive the line LOW, which means that it must sink current from the resistor.  The equation you are looking for is the most common in all of electronics -- Ohm's law.  The value of the current is not listed on our datasheet, because our device is not the one driving the line... it would be whatever controller you are using to turn on the SN74LVC1G240.

Both the low and high level output current have multiple values for 3V. Why?

This was a decision made ~40 years ago, I'm afraid I can't tell you what the designers were thinking at the time, but I can tell you that more information is better than less. If you are operating this device at or near 3V, then you have 2 datapoints to reference instead of 1. 

Why is 4.5V give as a VCC when 5V is more typical? Who would use 4.5V?

Note that this is true for all common voltage nodes in teh datasheet -- instead of 1.8V, we provide 1.65V, instead of 2.5V, we give 2.3V, instead of 3.3V we give 3V, and instead of 5V, we give 4.5V.  This is because no supply is perfect, and many have fairly large variations.  The performance of silicon gets worse as voltage is reduced, so we provide the worst-case values here (about Vcc - 10%) for each common supply case.

Is there any schematic to show what the out Y consists of electrically?

Is there any schematic to show what the in A consists of electrically?

Yes, and no.  There isn't a semiconductor company out there that will tell you _exactly_ how they design parts... however, CMOS design is very well documented and this device is (and all logic devices are) relatively simple. This one uses standard CMOS inputs and a push-pull output topology with a single pFET and a single nFET.  There's a nice video that details the internals of CMOS inputs and outputs located here:   (you can skip to 1:18 to see what I'm referring to).

So what's the ESD protection since it is limited? Can you be more specific on how the output is protected?

The device is protected by a standard ESD protection cell -- I can't go into detail on the design, however I can say that it's intended only for protection during manufacturing, and any system should have additional ESD at any exterior ports to prevent damage to the internal ICs.

I hope this is helpful to you.