Confusion regarding HC245 and HC541, HC vs HCT

[John Celo]

I'm looking at HC541 (unidirectional tristate-buffer/driver) and HC245 (bidirectional tristate buffer).

HC541 is specifically stated as a "driver". How exactly is HC541 a "line-driver" and HC245 not? They both seem to have similar performance characteristics. Main difference being bidirectionality of HC245.

I want to stock up and use HCT variant of 245 as a generic part in parts bin, which could also be used as a level shifter (3.3V->5V in output direction, because HCT part recognizes 2V as high input, and HC part needs 3.5V as high input) as well as fullfill all the functions of HC541 would.

HCT version being bit slower (about 2x slower max switching speed, but still in 10+ mHz range?) and costing bit more than HC versions.
HC245 are generally speaking also significantly cheaper than HC541 parts (LCSC pricing), so 245s also seem the way to go even if you don't require bidirectionality.
HCT245 seems like the choice to go to unless very fast switching speeds (on a bus) are required.

Am I understanding this correctly?

[David Hess]

HC541 is specifically stated as a "driver". How exactly is HC541 a "line-driver" and HC245 not? They both seem to have similar performance characteristics. Main difference being bidirectionality of HC245.

They are just calling it a driver based on application.  The drive capability of both integrated circuits is identical.

[CaptDon]

The 541 being stated as a driver is just as David said, the method in which it is typically used. Inputs that may consume one unit load with outputs that can drive 20 or 40 unit loads. Since it is uni-directional, a one way street it could drive LED's used as process indicators or status indicators. The 245 is bi-directional and termed as a 'buffer' because it has current gain in both directions therefore a CPU is able to drive an address or data buss and a single RAM replying back is also able to drive a heavily loaded buss by talking through a buffer. It's just a word usage convention when an engineer wants to search a data base specifically for a driver or a buffer. I have often seen 245's connected as a one way street in which case it would be considered a driver. Probably done to reduce the variety of part numbers in a project and maybe even get volume discount using more of one particular part number.

[cte]

Regarding HC and HCT, those documents might be helpful:

Logic Guide (Texas Instruments)

An Introduction to and Comparison of 74HCT TTL Compatible CMOS Logic (Fairchild / ONsemi)

[David Hess]

It is confusing because there are logic chips labeled drivers which do have increase output drive and can directly drive a low impedance transmission line.  The 74HC541 is not one of these chips.

[edavid]

I think what happened was that the original 74F541 (or 74LS541, not sure what came first) part did have high current outputs, and then when they made the 74HC versions with standard outputs, they didn't want to change the description.