The 4046/74HC4046-series phase-locked-loop ICs are extremely useful parts that can be used in a lot of applications like frequency synthesis/multiplication, signal synchronisation, data extraction etc.
Unfortunately, many first users have run into difficulties due to misleading (and very old/never revised) data sheets and erroneous application notes.
This note will show you how to interpret the information from the suppliers and let you use the 4046 successfully; all based on my own painful experiences.
At the end, we’ll do a step-by-step design example.
Now, first wrinkle -- and, a fatal one I think, as, at a glance, I don't see this enumerated in the article -- CD4046 is the "original and still best", and 74HC4046, and 7046 and 9046, are the knock-off substitutes. Perhaps that is where the confusion has arisen?
You would think they could simply port them over from metal to silicon gate CMOS and be done with it, but no; they absolutely ruined them (so I understand it). The oscillator is terribly inconsistent (part-to-part variation), and nonlinear. The type 2 phase detector has a terrible dead band. (Whereas the CD4046 had slight overlap, so that it could lock on the margin with very high gain and no dead band.)
The others are improved versions, but as I've heard it, none of them are as capable as the original, they're only faster and operate at lower voltage.
Tim
"So, what’s going on here? Each of the HC4046 manufacturers
uses a different circuit for their VCO design.
Although intended to be predictable and linear, in practice
the VCO control is nonlinear, and its parameters vary with
control current, supply voltage, and operating frequency,
especially above 10 MHz. Although you can find analyt-
ical expressions for the VCO’s frequency (ON Semi app
note AN 1410), the recommended method is still to start
with the timing component values (R 1, R2, and Ci) from
datasheet graphs; then the designer is sternly admonished
to adjust and validate those values with careful bench
measurements before committing to manufacturing.
This sort of variability and lack of confident predictability
leads us to render this advice:
1. choose one manufacturer for your production design,
and do not allow substitutes;
2. choose a wide safety margin for and / max, such as
the 3 x factor in our Figure 13.99;
3. replace your initial paper calculations with measured
bench values for production.
Rule 1. applies to any linear functionality in a logic
IC, e.g., mixed-signal functions such as phase comparators,
oscillators, VCO's, mixers, Schmitt-triggers, monostables,
or comparators."
The first time users may be trying to get a PLL running until cows come home and never succeed, because of the limitations Tim pointed out. To me Tim provided valuable information and you may need to pass it over to your friend.
Waffle is necessary, as I don't have much experience with them myself -- I know people that do, I can provide contact if you like.
Also don't have enough experience to talk about loop compensation, but that is always a thing to look out for. If you don't allow some hours to test component values during bring-up, you're going to have a bad time. A particularly insidious case when the datasheet claims to know the way!
Tim
So why on earth did you derail this thread right away? But I'm glad you 'fessed up. Hats off to you, Sir!
So why on earth did you derail this thread right away? But I'm glad you 'fessed up. Hats off to you, Sir!
Because that's how forums work, you post a thought and people reply with whatever comes to mind. Alas, we all suffer this frustration. You can't say you didn't get what you paid for.
Tim
Next up: a direct digital synthesizer built from 12SQ7s. These 4046-family chips are all genuine antiques, and should be considered to be primarily of historical interest. Too many nicer parts out there that actually work well.
As Karel says, the 74HCT9046A seems to be the latest of several generations, and its data sheet says there's no dead zone. It would probably be the best one to use if you want to experiment with a 4046-type part. No DIP package, unfortunately...
Next up: a direct digital synthesizer built from 12SQ7s. These 4046-family chips are all genuine antiques, and should be considered to be primarily of historical interest. Too many nicer parts out there that actually work well.What are your favorites, especially for 1kHz to 1MHz frequencies?
74HCT9046AN is obsolete, but available from eBay or utsource.net
AFAIK, CD4046 are fine, 74HC4046 are crummy.
Now, first wrinkle -- and, a fatal one I think, as, at a glance, I don't see this enumerated in the article -- CD4046 is the "original and still best", and 74HC4046, and 7046 and 9046, are the knock-off substitutes. Perhaps that is where the confusion has arisen?