6

FN2920.10

April 12, 2007

PIN COMPATIBILITY

The basic pinout of the 8-pin device corresponds, where

possible, to that of the industry standard 8-pin devices, the

LM741, LM101, etc. The null-storing external capacitors are

connected to pins 1 and 8, usually used for offset null or

compensation capacitors, or simply not connected. In the

case of the OP-05 and OP-07 devices, the replacement of

the offset-null pot, connected between pins 1 and 8 and V+,

by two capacitors from those pins to pin 5, will provide easy

compatibility. As for the LM108, replacement of the

compensation capacitor between pins 1 and 8 by the two

capacitors to pin 5 is all that is necessary. The same

operation, with the removal of any connection to pin 5, will

suffice for the LM101,

μA748, and similar parts.

The 14-pin device pinout corresponds most closely to that of

the LM108 device, owing to the provision of “NC” pins for

guarding between the input and all other pins. Since this

device does not use any of the extra pins, and has no

provision for offset-nulling, but requires a compensation

capacitor, some changes will be required in layout to convert

it to the ICL7650S.

Typical Applications

Clearly the applications of the ICL7650S will mirror those of

other op amps. Anywhere that the performance of a circuit

can be significantly improved by a reduction of input-offset

voltage and bias current, the ICL7650S is the logical choice.

Basic non-inverting and inverting amplifier circuits are shown

in Figures 2 and 3. Both circuits can use the output clamping

circuit to enhance the overload recovery performance. The

only limitations on the replacement of other op amps by the

ICL7650S are the supply voltage (

±8V Max) and the output

drive capability (10k

Ω load for full swing). Even these

limitations can be overcome using a simple booster circuit,

as shown in Figure 4, to enable the full output capabilities of

the LM741 (or any other standard device) to be combined

with the input capabilities of the ICL7650S. The pair form a

composite device, so loop gain stability, when the feedback

network is added, should be watched carefully.

Figure 5 shows the use of the clamp circuit to advantage in a

zero-offset comparator. The usual problems in using a

chopper stabilized amplifier in this application are avoided,

since the clamp circuit forces the inverting input to follow the

input signal. The threshold input must tolerate the output

clamp current

system.

The pin configuration of the 14 pin dual in-line package is

designed to facilitate guarding, since the pins adjacent to the

inputs are not used (this is different from the standard 741 and

101A pin configuration, but corresponds to that of the LM108).

FIGURE 1A. INVERTING AMPLIFIER

FIGURE 1B. FOLLOWER

FIGURE 1C. NON-INVERTING AMPLIFIER

FIGURE 1. CONNECTION OF INPUT GUARDS

+

-

INPUT

OUTPUT

+

-

INPUT

OUTPUT

+

-

INPUT

OUTPUT

R

1

R

2

R

1

R

2

+

----------------------

NOTE:

SHOULD BE LOW

IMPEDANCE FOR

OPTIMUM GUARDING

7650S

+

-

0.1

μF

OUTPUT

C

R

C

CLAMP

INPUT

0.1

μF

For Full Clamp Effect

FIGURE 2. NON INVERTING AMPLIFIER WITH OPTIONAL CLAMP