🚀 go-pugleaf

In article <7116@m1.cs.man.ac.uk> Mark Robinson,
mark-r@spec0.ee.man.ac.uk writes:
>If anyone has a datasheet for the 74HC4046 PLL chip handy would
>you let me know how the frequency of the VCO is related to the
>values of R's and C and the max/min values that they can take.
>
>I want to run it with a lock range of about 1MHz, centred on
>8MHz, but the equations in the Maplin catalogue don't allow
>frequencies >2.8MHz (R=5k, C=50pF; ie the minimum allowed) even
>though they claim the VCO can get up to 15MHz. I think their
>data must be for the 4046 and none of our databooks are modern
>enough to include the 'HC4046 :-(

Something you should be aware of is that all HC4046's are NOT 
created equal. Two extremes I have found are
1 : An SGS device that was barely able to oscillate at  1 MHz
(and the output waveform was triangular at that frequency)
and -
2 : An RCA device that was still producing respectable square
waves at 10 Mhz
(Both devices running into a scope probe only , 5 volt supply)

At the frequency you want (8 Mhz) the design nomographs
become a bit irrelevant, as internal Cs & Rs dominate the issue.

I was driven to using LS124/324s, but i only wanted the vco
function, no doubt someone makes a better PLL.
cheers,
	Mike.