Page 201 - Troubleshooting Analog Circuits

Appendix B

Operational Amplifiers with
Nonstandard Pinouts

The other day I was writing to an old-timer and explaining that the new IC op amps
are not only as easy to apply as the old vacuum-tube ones, but in many respects
easier. I began to explain that the LM607 is easy to use and to trim for offset voltage,
and so is the LF355, and-woops! Yes, each one is easy to trim, but they have dif-
ferent trim schemes. The LF356 needs a trim pot from pins 1 and 5 to +Vs, whereas
the LM607 needs a pot from pins 1 and 8. Furthermore I recall some people griping
that NSC’s LF35 1 has trim pins for which you turn the trim pot one way to increase
the VOs and the LF411 has trim pins for which you turn it the other way. Then one
time a few years back, we started shipping LF411s marked as LF35 1, as an
“improvement.” Oh, yes, many customer were probably pleased by the “improve-
ments,” but some customers were peeved because we had reversed the gain of their
trim circuit. So why do I spend my time griping about MM74C86s that have non-
standard pinouts, and ignoring the problems with linear ICs?!?! So, here you are.
First item, these lists apply only to single operational amplifiers in 8-lead pack-
ages, metal or plastic. Next, the pins 2,3 and 6 are always the inputs and output.
Next, pins 4 and 7 are always the - and + supplies. Next, the 8th pin-the one that’s
left after the two trim pins are assigned-is almost never standardized, and I am not
even going to mention it here. In some cases it’s an over-comp pin, and other times it
has other functions. No comment.
Nonstandard Pinouts:
LM709 LM101, LM301

LM107, LM307 LMlO8, LM308
LM118, LM318 LM144,LM344
LMlO LH0024
(These are all mongrel and nonstandard compared to anything else. Refer to the
individual data sheets.)

TYPE I- I O-ka pot to -Vs from pins I and 5.
LM741 ‘i

LM143 (100 kR) F
LM776 (100 kR)
LM4250 (100 kR)

LF351 -VS 1 OK
LF411
LF441 Figure 8.1. Type I: Pins I and 5 Trim to -V5
I 88