What I meant was the minimum guaranteed maximum operating frequency for all such chips produced. Anyway, I just noticed the frequency difference. I was looking at the datasheet for the Philips 74HC4046A during my design. The Philips part specifies a guaranteed _center frequency_ of 11MHz, more than 4 times faster than that of the National/Fairchild part. Maybe the "A" part number suffix that I missed said it all. Oh well, I have a TI CD74HC7046A that operates at the right speed, according to the datasheet from TI. ----- Original Message ----- To: "Multiple recipients of list CHIPDIR-L" <[EMAIL PROTECTED]> Sent: Thursday, August 12, 2004 3:35 AM
> National is not making these chips anymore but has moved its logic > line to Fairchild again. Hence the corresponding datasheet for your > device would be the one on > > http://www.fairchildsemi.com/pf/MM/MM74HC4046.html > > which states a significantly lower "maximum operating frequency" for > the VCO, and not at all a "maximum center frequency"! > > Uwe. > > > > BOD> Yes, I was breadboarding the circuit. Out of curiosity, I measured the > BOD> capacitance between adjacent terminals and found from 5 to 7 pf of > BOD> capacitance. I guess I'll have to make a demonstration circuit for myself > BOD> on a PCB. Hey, I could use both the MM74HC4046 and LMC555 in the same > BOD> circuit, using the LMC555 as the timebase! > > BOD> I don't recall that there's anything wrong with tying the VCOin pin to Vcc > BOD> as a convenient way to generate the max. VCOout, it's just that the response > BOD> is only linear .9V to 1.1V from each rail. > > BOD> My chip is a National MM74HC4046N. > > BOD> Brad > BOD> ----- Original Message ----- > BOD> To: "Multiple recipients of list CHIPDIR-L" <[EMAIL PROTECTED]> > BOD> Sent: Wednesday, August 11, 2004 1:00 PM > > > >> I think, it's not allowed to just tie the vco input pin logical "high" > >> (Vcc). > >> Use some other (lower) voltage (e. g. Vcc/2). > >> The vco has its input voltage range, and that doesn't go from rail to > BOD> rail. > >> I don't know, what will happen if the input is beyond its limits, but this > >> could be the problem. > >> And which manufacturer is the chip from? > >> > >> Steffen Maisch > >> > >> -- > >> Author: Steffen Maisch > >> INET: [EMAIL PROTECTED] > >> > > > > -- > Author: Uwe Zimmermann > INET: [EMAIL PROTECTED] > > Fat City Hosting, San Diego, California -- http://www.fatcity.com > --------------------------------------------------------------------- > To REMOVE yourself from this mailing list, send an E-Mail message > to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in > the message BODY, include a line containing: UNSUB CHIPDIR-L > (or the name of mailing list you want to be removed from). You may > also send the HELP command for other information (like subscribing). > -- Author: Brad O'Dell INET: [EMAIL PROTECTED] Fat City Hosting, San Diego, California -- http://www.fatcity.com --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB CHIPDIR-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
