7402 Pinout Difference

[jack0987]

Looking up images for the pinout of the 7402, two versions came up.
Is this common?
Which is correct?

 

[shortbus=]

Yes, on many things. That is why you always use the data sheet from the company your part came from.

 

[AnalogKid]

Both images are correct.

The image on the left is for a CMOS CD4001. This is NOT directly equivalent to a bipolar SN7402 in the right image, either electrically (voltages and currents) or physically (pinout). Note that the left image power pin is Vdd (the correct designation for a CMOS part) as opposed to the right image of a Bipolar TTL part with a power pin labeled Vcc. This is because a bipolar transistor has a collector (c) while a CMOS transistor has a drain (d).

cc stands for common collector, a type of amplifier circuit. When FET logic came about, they changed the last letter to d for drain. Rather than use the technically correct Vcd (Voltage, common-drain), they went with dd for consistency and error reduction

ak

 

[jack0987]

Thanks for the response.

I am using the TTL one (an MC74HC02) on the right.

Is it good practice to to ground all unsed inputs?

 

[Nigel Goodwin]

Thanks for the response.

I am using the TTL one (an MC74HC02) on the right.

Is it good practice to to ground all unsed inputs?

Probably, a lot depends on the circuit configuration in the chips (might be better both high, might already be pulled high or low internally?), and if you're wanting minimum power consumption - it's more of an issue in CMOS, where inputs can drift and put the gate in an analogue state, greatly increasing consumption.

 

[AnalogKid]

I am using the TTL one (an MC74HC02) on the right.

That is a CMOS version of a TTL part, so the TTL pinout is correct for this part.

Is it good practice to to ground all unsed inputs?

Ground or Vdd (Vcc), doesn't matter. But only the unused inputs. Leave all unused outputs floating.

ak