LS/HCT/etc. logic familes

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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...

LS/HCT/etc. logic familes
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

Re: LS/HCT/etc. logic familes
On 07/10/2017 02:08 PM, snipped-for-privacy@gmail.com wrote:
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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
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Re: LS/HCT/etc. logic familes
On 2017-07-10 11:08, snipped-for-privacy@gmail.com wrote:
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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 :-)


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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/

Re: LS/HCT/etc. logic familes
On Tuesday, July 11, 2017 at 9:21:27 AM UTC-7, Joerg wrote:
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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?


Re: LS/HCT/etc. logic familes
On 2017-07-11 09:55, snipped-for-privacy@gmail.com wrote:
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You'll need a level translator such as this:

http://www.ti.com/lit/ds/symlink/cd4504b.pdf

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/

Re: LS/HCT/etc. logic familes
On 07/11/2017 01:55 PM, Joerg wrote:
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If you have spare inverters/NAND gates/etc does the "trick" you often  
see of using them in parallel to drive a FET gate actually work well or  
is that just old wive'ss tale "engineering voodoo"

Re: LS/HCT/etc. logic familes
On Tue, 11 Jul 2017 14:45:46 -0400, bitrex

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That can work fine.


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: LS/HCT/etc. logic familes
On 2017-07-11 11:55, John Larkin wrote:
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Yep. But you have to weigh the cost of a hex inverters chip against two  
BJT and at least for Asian production the BJTs always win. Unless you  
had 4-5 inverter vacant anyhow for some reason, which is rare.

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: LS/HCT/etc. logic familes
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Gate drive can be built economically with both: use one gate to drive a  
complementary emitter follower.  Or use two gates, one to drive the gate as  
such (holds the gate with zero saturation voltage), the other to drive the  
emitter follower.

The emitter follower usually "drools" a bit and overshoots the theoretical  
0.7V-below-rail saturation point, which is fantastic to begin with.  Just in  
case, the extra gate provides a modest holding force to keep it near the  
rail.

Coincidentally, just the other day, I breadboarded this with a 74HC14 and  
2N4401/3 at 3.0V.  Into a 4nF equivalent gate, I get 50ns edges, not bad.

Even better with low-Vce(sat) type transistors, like PBSS303NX/PX.  The high  
hFE will give excellent results even with CD4000 logic, or a somewhat  
cheaper, still highish hFE BCxxx something or other, since you won't be able  
to utilize the full current capability of those.

Tim

--  
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
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Re: LS/HCT/etc. logic familes
On 07/11/2017 03:48 PM, Tim Williams wrote:
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Send teh codez send schem

Re: LS/HCT/etc. logic familes
On 2017-07-11 13:20, bitrex wrote:
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You can also just do a PNP/NPN follower and run a resistor of several  
tens of ohms from the bases to the emitters. Zetex (now Diodes Inc)  
makes good pairs and they cost around 20c inqties if that's in the budget:

https://www.diodes.com/assets/Datasheets/ZXGD3006E6.pdf

Way I use them is to tie the emitters together and then to the FET gate  
to be driven. VCC to V+, VEE to GND, IN to the driving gate. Resistor  
from IN to the FET gate.

None of ze codez needed :-)

If not in the budget I use two BJT de la maison, whichever is least  
expensive. The topper in that respect was a company in South Korea. They  
had long computer print-outs hanging all along one of the hallways.  
Those contained the daily pricing of a lot of such parts, like a really  
long stock ticker. The carpet in front of that wall was very worn and  
there were lots of burn holes in it (engineers were allowed to smoke  
there and unfortunately most did).

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: LS/HCT/etc. logic familes
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Well, if you must...
https://www.seventransistorlabs.com/Images/BoostedLogicGateDrive.png
basically what I described. :o)

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That saves a gate, and works reasonably well, outside of logic-level use.

The downside is, the transistors only boost when the resistor voltage drop  
exceeds Vbe.  So, a CD4000 gate would never get any assistance with that low  
of a resistor (>= 220 would be fine though).  74HC would get a boost after a  
couple of volts, but that wouldn't be of much use against a logic-level  
MOSFET that's already gone through the Miller plateau.  So, 100-220 would be  
better there as well.

The resistor will also delay boost, and clear stored charge more quickly, so  
you probably won't get the overshoot bonus, either. :(

So, for logic-level use, you might be better off without the resistor at  
all...

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I find it amusing (or slightly infuriating) that they find it fit to call it  
a "gate driver", when it's painfully obvious from the datasheet that it's  
just two discrete transistors.

I wonder why they did that.  Marketing?  Does no one understand how to use  
BJTs anymore?  (Well, probably. :( )  They don't give any tips on how to  
generate that nice big voltage swing, either (tens of volts in a couple  
nanoseconds, you say?  That's /fantastic/!..), which is the bigger problem  
when making a driver.  (On a similar rant: TI is mum about what magical gate  
driver they used to test their NexFETs.  "R_G = 0 ohm".  Yeah, sure.)

In any case, the transistors themselves are great, whether you buy singles,  
duals (ZXTDxxx I think) or these so-called "gate drivers". :)

Tim

--  
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
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Re: LS/HCT/etc. logic familes
On Wednesday, 12 July 2017 00:45:48 UTC+1, Tim Williams  wrote:
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I'm puzzled, that looks like a buffer overpowering the output of the bottom chip.

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Re: LS/HCT/etc. logic familes
On Thursday, July 13, 2017 at 10:54:36 AM UTC+2, snipped-for-privacy@gmail.com wrote:
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It's really just the output impedance of the emitter follower into the other gate. So for large signal slew, the emitter follower is boss, for low voltage, the other gate is the driving device

Cheers

Klaus

Re: LS/HCT/etc. logic familes
On Thursday, 13 July 2017 14:51:17 UTC+1, Klaus Kragelund  wrote:
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Yes, I realised after a bit of thinking. It's not a circuit technique I'm familiar with.


NT

Re: LS/HCT/etc. logic familes
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I've never seen it in discrete form before, but I have seen it in ICs:
https://www.fairchildsemi.com/datasheets/FA/FAN3122T.pdf

If you think of a gate as a pair of MOSFETs instead of a digital component,  
all becomes clear. :)

Tim

--  
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
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Re: LS/HCT/etc. logic familes
On Thu, 13 Jul 2017 18:05:52 -0500, "Tim Williams"

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LM5112 is similar.


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: LS/HCT/etc. logic familes
On 2017-07-13 19:57, John Larkin wrote:
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Problem is, they are expensive. For normal jobs a Zetex (now Diodes Inc)  
pair behind a gate plus a resistor is less expensive. When every cent  
counts then it has to be two discrete BJT.

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: LS/HCT/etc. logic familes
wrote:

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We're paying 73 cents each. We don't care about parts cost as much as
assembly labor, which includes setup for pick-and-place. So for us,
simpler is usually worth more than pure cheap parts cost.

We do tricks with quad r-packs to get various resistance values and
divider ratios from one value of pack. That keeps the BOM line count
down, and reduces feeder setup.

The LM5112 lets us have an output V- below ground, which is handy some
times, and would take more discretes to do. And it has peak drive of
7/3 amps at 15 volts p-p.

IXDN602 is cool too. Dual fet driver, 2 amps, 35 volts, 7 ns
rise/fall, 77 cents. With a driver that brutal, sometimes you don't
need the fet!


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


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