donald wrote:
HEF4046BCN`s, but have
recently read that this CMOS IC has a design flaw. What would be a better
chip to retrofit?
As Bill said, the HCT9046 is the improved version of the 4046.
The "flaw" in the 4046 is a dead zone around zero error in Phase
Comparator 2 (the PC one generally uses). PC2 in the HCT9046 uses
charge-pump outputs that are biased to avoid the dead zone. It also
uses an internal voltage reference, rather than fraction-of-Vdd, to
minimize drift.
Note that the 9046 is HCT only (no HC version), meaning that its input
transition points are TTL standard (not 1/2 Vdd, like normal CMOS logic
such as HC).
Also note that the HCT9046 has only two phase comparators (PC1 and PC2),
and does not have the 4046's PC3 (this is true also of the various 7046
chips, although they do not share the dead-zone improvement of the 9046).
Best regards,
Charles
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