[time-nuts] 4046 replacement

Charles Steinmetz csteinmetz at yandex.com
Wed Apr 18 09:17:05 EDT 2018


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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