13 Sep
2004
13 Sep
'04
10:28 a.m.
From: "Bill Sudbrink"
<wh.sudbrink(a)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