[time-nuts] 74HCT9046A Max. Operating Frequency

Attila Kinali attila at kinali.ch
Thu Apr 24 11:59:41 UTC 2014

On Thu, 24 Apr 2014 09:41:44 +0100 (BST)
sg sg <micpreamp at yahoo.de> wrote:

> I'm about to implement a PLL for a 24.576 MHz VCXO using the phase-frequency
> detector (PC2) of the NXP 74HCT9046A. From the datasheet (www.nxp.com
> /documents/data_sheet/74HCT9046A.pdf) it is not clear to me what the maximum
> operating frequency for this phase detector is--from the enable and disable
> times (page 20 and figure 19) I presume 24.576 MHz is too much.
> So I probably need to add dividers at the inputs. Can someone advise me on
> the choice of division ratio?

Actually, unless i have missed it, there is no specification of the
maximum operation frequency of the phase comparators.
I guess they assume that everyone is using it the build in VCO
which maxes out somewhere around 25MHz (not guaranteed, see Fig23b)

So, 27.6MHz should be probably possible. Try it :-)

Alternatively you can go to Linear or Analog Devices and buy one of
their PLL's that have a specified upper frequency.

			Attila Kinali

The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
		-- Tirin, The Dispossessed, U. Le Guin

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