At 11:17 02/06/2003 -0700, you wrote:
I would like to use the M74HC4060 as a 'divide-by-64' signal source. Can
anyone tell me the upper limit for xtals that this chip can handle? My xtal
will be on 8.750000; I fear that the upper limit may be around 4-6 MHz?
Steve
Dear Steve, LF Group
According to the National Semiconductor data book, the 74HC4060 has a
guaranteed minimum operating frequency of 30MHz at 5V supply. Over the 2 -
6V supply range, typical values are 6MHz and 35MHz respectively.
The slower 4000 series CD4060 device operates over a wider voltage range -
at 5V supply, guaranteed minumum frequency is 1.5MHz (4MHz typ); 10V, 4MHz
(10MHz typ), 15V - 5MHz (12MHz typ). So it is a bit "iffy" for 8.75MHz, but
it might be worth selecting a good one if, for example, you wanted
everything to work from a 12V rail.
These figures really relate to the divider part of the chip. As far as the
crystal oscillator part goes, this depends a lot on the crystal and the
external components, since the "oscillator" is just a CMOS inverter which
provides gain (although the 74HC4060 inverter has been optimised for xtal
osc use by increasing the output impedance). But experience shows that an
xtal around 9MHz will be no problem for the 74HC device, and will almost
certainly work with the 4000 series device too. For details of the
oscillator section design, have a look at
www.fairchildsemi.com/an/AN/AN-340.pdf
Cheers, Jim Moritz
73 de M0BMU
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