2114 Static RAMs...

[Dwight K. Elvey]

>From: "Bill Sudbrink" <wh.sudbrink at verizon.net>
---snip---
>
>Another data point plus an "Arg!"...
>Ohio Scientific was quite fond of 2114s (Arg!).  It looks like
>the cause of the power supply failure in my C4P is that one of
>the 24K memory cards (48 2114s) was drawing well over spec, even
>though it appeared to be providing reliable memory operation.  It
>was populated with the LC (low power CMOS) 2114 chip.  According
>to specs on the web, these should draw 40 milliamps max.  I pulled
>10 at random.  Not one pulled less than 70.  Now, I tested them
>with all pins floating other than power and ground and I wonder
>how much difference that makes, but totaling up an average of 75
>per chip gives about what the card as a whole draws when in
>operation.  The other card, populated with another vendors 2114s,
>draws over 1/2 amp less when in operation, reflecting about 42
>milliamps per chip.
>

Hi
 Floating of CMOS inputs may draw a lot more current. These
are not like TTL in this respect. CMOS inputs will tend
to float until current flows through both the input P and
N channel transistors. This is bad for the parts as well as
drawing current. CMOS inputs should always be high or low
while testing power supply current.
Dwight