<HTML><FONT FACE=arial,helvetica><HTML><FONT SIZE=2 PTSIZE=10 FAMILY="SANSSERIF" FACE="Arial" LANG="0">In a message dated 8/27/2005 2:56:32 PM Central Standard Time, alvitar@comcast.net writes:<BR>
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<BLOCKQUOTE TYPE=CITE style="BORDER-LEFT: #0000ff 2px solid; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px; PADDING-LEFT: 5px">I'm not familiar with that specific part, but the differences<BR>
between 40xx, 74HCxx, and 74HCTxx parts are primarily related<BR>
to supply voltage and input thresholds.<BR>
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40xx: Vdd ranges from +5V to +15V<BR>
74HCxx: Vdd +5V, CMOS compatible input levels<BR>
74HCTxx: Vdd +5V, TTL compatible input levels<BR>
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Within the 4046 devices alone, there are significant differences amongst manufacturers. Some have a built-in preamplifier while others do not. That radically changes the apparent sensitivity to the phase comparator inputs. The 4046s that I have (Motorola brand) DO have the preamp in them and have a lock sensitivity of about 80 millivolts P-P. Other brands did not have this preamp and did not work in my application. As that variation did not even involve 74xxxxxx series parts, I would make certain to study the datasheet for the chip from the manufacturer of the chip you actually buy.<BR>
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I would suggest you get datasheets from all manufacturers from whom you might potentially buy, and compare them spec by spec. That might just change your choice of manufacturer ... it did for me!<BR>
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Peace.<BR>
Tom Farrand<BR>
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