LS/HCT/etc. logic familes

Is LS logic still at all relevant for new designs? Is HCT logic still at all relevant for new designs? Is the 74xx/4000-whatever series still at all relevant for new designs? Do you use them at all regularly in your work, or have you moved on to more modern families (or Just Use A PIC)?

They still have many "LS" series ICs available in fairly large quantities at the usual distributors, in SMD packages even. So I assume someone must use 'em for something. Inquiring minds want to know...

Reply to
bitrex
Loading thread data ...

I never use LS, but a lot HC, HCT and 4000. Nothing really beats the 15V supply of a 4000, 4093 being my favorite

But these days it's most driver ICs, since microcontrollers cost only as much as 2 HCTs

Cheers

Klaus

Reply to
klaus.kragelund

LS is completely irrelevant garbage. In its day it was a great replacement for standard TTL working at same speed but 1/3 the current consumption. Thi s junk is for maintenance of existing old products and hobbyists. Dunno who would use it for a modern product.

Reply to
bloggs.fredbloggs.fred

Well, not new designs, but I still use 4000 chips in a PWM servo amp for brush motors that runs directly off 12 V, same as the FET gate drive supply. Makes things really simple.

I have a brushless servo amp that uses a Xilinx CPLD running off 3.3 V, so if the 4000 family eventually becomes unavailable, I could update the brush version to use the same.

I use a lot of CPLDs and FPGAs in the other stuff I design, so not much

74xxx in anything now. About the only thing else is voltage level translators and a 4538 one shot as a watchdog.

Jon

Reply to
Jon Elson

HC is alive and well. 5V isn't much used for logic anymore (if your functions aren't sucked up into an MCU or FPGA, you're wasting a ton of board space and probably parts cost*), but is great for glue logic, line drivers and receivers, etc. Anything faster or newer (like LVC) is great for similar things at lower voltages (though, LVC is technically rated for

5V!) and higher speeds.

*The threshold feels like somewhere around 0 to 4 logic chips. Even if you're not using a bargain basement MCU, it gets very economical to use one to replace more than a few logic chips. Even more so when you're talking about replacing more logic chips with a small FPGA.

LS is still around, but I certainly wouldn't use it for new designs. CMOS is better in all respects, and HCT parts are available if you need the input threshold.

CD4000 is still around, and has no alternatives for high voltage logic -- unless you want to cook your own from transistors! It's unfortunate that it's so slow and gutless, but when you don't need fast logic and you're just gluing some things together in an analog circuit that doesn't even have a 5V supply: it's absolutely perfect.

As for packages, everything is available in DIP and SOIC. (Heck, there might be fewer in DIP than SOIC, I'm not sure. DIP is slowly going away, and you should be prepared for SMT!) Some is also TSSOP, unfortunately the less common ones usually aren't. CD4000 I think doesn't usually come in TSSOP. Receivers like 74HC7014 aren't available in TSSOP.

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
 Click to see the full signature
Reply to
Tim Williams

LS was slow and had terrible noise immunity and metastability. There's no reason to use it in a new design. Not many people still make it.

HC/HCT is OK for general glue logic. Or the various TinyLogic parts.

I use HC (the schmitts are nice) and HCT, and some Tiny parts for their speed. And some ECL and CML for extreme speed. Most "logic" is in uPs and FPGAs now, so HCT type parts are mostly buffers and little utility circuits.

--
John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
 Click to see the full signature
Reply to
John Larkin

I use LS for hand-prototyping little hairball logic circuits sometimes because static sensitivity is less of an issue, and I've got a box full of 'em with just about ever part # represented

Reply to
bitrex

Not just static sensitivity - apparently LSTTL is much rad-harder than cmos. But not making stuff that gets irradiated I haven't used LSTTL since the 1980s.

As others have written 4000 is still great when speed isn't needed but operating from rails above 5V is. Really useful for hairball interfacing to mickey-mouse analog and descrete circuits. At 15-18V Vdd CMOS can sink/source pretty hefty current!

I use plenty of analog switches like HC4051/52/53 and a few shift regs and counters but now hardly use any gate logic HC or LVC because microcontrollers are so cheap and flexible.

piglet

Reply to
piglet

I use a lot of HC405x-family muxes. I also use a fair number of HC4017s for sequencing in protos and the occasional HC4046, flipflop or counter chip, especially in PLLs. (The HC4046 is useful only for its phase-frequency detector.)

You can do a lot of tricks with the 4046, including switching sidebands in an offset loop by inverting the gain of the loop amp.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
 Click to see the full signature
Reply to
Phil Hobbs

Use LVC, or some variation.

Reply to
krw

I use many shift registers such as the 74xx595 or '166 for low speed I/O expansion for microcontrollers and FPGAs.

Oh, and a zillion SN74AVC16T245 for level shifting.

Allan

Reply to
Allan Herriman

TPIC6595 is similar, but has zener-clamped open-drain power outputs. It's a great relay or LED driver.

--
John Larkin         Highland Technology, Inc 

lunatic fringe electronics
 Click to see the full signature
Reply to
John Larkin

bitrex wrote on 7/10/2017 1:29 PM:

This is an odd question. Why do you care what others are using them for? LS and HCT logic come in two flavors, SSI/MSI and LSI. The SSI/MSI devices would only be used in new designs that need a tiny amount of logic but are high volume to be very cost sensitive (a very small percentage of designs today). The LSI devices such as bit slice, ALUs, etc., can be implemented easily in programmable logic likely at a lower cost and power.

So other and maintaining obsolete equipment there is very little demand in new designs for discrete logic.

I was working on a new design for a military radio once where they needed an SPI receiver to control a few I/Os, relays, etc. This is just a couple of shift registers and a wee bit of random logic totaling some five or six very low cost devices in very small packages. I was told to use an MCU so the design could be "flexible". This required a crystal, the MCU, a power regulator, a reset chip, a programming interface,... I am happy to use MCUs where they have an advantage, but this was one case where the function was very fixed and the MCU was a bit of a PITA. But they already had some two dozen MCUs in the product, I guess what is one more?

--

Rick C
Reply to
rickman

I second that. Same here.

In the 90's a sales engineer from a major IC manufacturer seriously told me that designing with 4000 logic is foolish and that the series would soon be obsoleted. I think it was him who was the fool :-)

True, but unfortunately many uC cannot be operated at 5V anymore and

3.3V does not cut it for driving FETs hard enough. Plus us analog guys need a programmer and depending on the uC family that might not be a local person. Local is sometimes needed when the circuit is inside a larger experimental set.
--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Why wouldn't I? Is it a bad plan to know how other people in the industry practice their trade? Why ask questions. Why do anything at all, I guess...

Ok that was very informative, thank you :-)

Reply to
bitrex

OK, thanks. Just ordered a bunch of 4050 to try out. But at 15V supply, Vih is still too high at 11V. Do i cascade a few chips at different supplies? If so, at what levels? 5V, 10V and 15V?

Reply to
edward.ming.lee

Yep. 74HC4xxx versions of the old-line 4000-series are readily available.

...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
 Click to see the full signature
Reply to
Jim Thompson

A uC needs a program, which needs to be properly documented and formally released. Then each chip needs to be programmed. That can cost kilobucks, so it will take a lot of production units to justify that. A few MSI chips is often the pragmatic way to get things done.

--
John Larkin         Highland Technology, Inc 

lunatic fringe electronics
 Click to see the full signature
Reply to
John Larkin

You'll need a level translator such as this:

formatting link

But watch out for power supply sequencing issues which may not always be well documented for the various ICs. Also, it's no good for 3.3V logic, there you'd need other translators.

Keep in mind that CD4000 logic does not have powerful outputs. When I use them in switch-mode converters I generally follow with a NPN/PNP pair. It is generally not good to mix logic families unless there is a compelling reason. In my cases that compelling reason was cost. However, if cost is not essential down to the last penny there are plenty of FET driver ICs which can be controlled by TTL level or less.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Even the CD4000 series is. They are essential in many apps where you do not have a well regulated supply or where the supply consist of a 9V battery. Or alarm systems and such with a 12V battery. There you can't use 74HC.

Any (hopefully good) news on your health?

[...]
--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.