Re: The 74L72 IC


Miroslav Pokorni
 

Well, John, you got me to dig out the collector's item, hardbound TI's TTL
book. The power ratio is around 10:1, specifically, plain 7472 draws 10 mA
typical, 20 mA maximum, while Low Power does 0.76 mA & 1.44 mA. Input
current for low level is 3.2 mA vs. 0.36 mA.

The low power device must have been dropped from product line early on. The
hardbound book, second edition (copyrighted 1976) lists low power, but a
later book from 1988 does not, though there are number of other low power
devices listed in the later book.

Regards

Miroslav Pokorni

----- Original Message -----
From: "John Doran" <johnd@epiloglaser.com>
To: <Tekscopes@yahoogroups.com>
Sent: Thursday, November 06, 2003 2:57 PM
Subject: [TekScopes] The 74L72 IC



Howdy! I thought I'd add my two bits to the discussion of this
IC.

Miroslav was being generous--standard TTL actually requires
*ten times* as much power as L TTL! Still, I cannot imagine
that one hotter logic chip would load the 'scope's power supply
excessively. The more likely problem is that whatever drives the
74L72's inputs might not be able to handle standard TTL.

I'd bet that you could substitute an LS TTL part with no problems,
but--total bummer--the 7472 was an old design that, as far as I know,
was only made in standard, L, and H TTL variants (H TTL requires
twice the power of standard TTL).

There appear to be no direct, pin-compatible replacements
for the 74L72 in any more recent logic family. Further, it's not
just a flip-flop; it has gated J and K inputs. It seems to me that
there are only two solutions here; you must find the same part or
you must wire up an equivalent circuit (I'd use 74 HCT) on
some sort of kluge-board.

Oh, one more thing--you can use a 54L72 (military version).

-John

Join TekScopes@groups.io to automatically receive all group messages.