The 14-pin DIP configuration has been specifically

designed to ease input guarding. The pins adjacent to

the inputs are not used.

Pin Compatibility

The ICL7653’s pinout generally corresponds to that of

industry-standard 8-pin devices such as the LM741 or

LM101. However, its external null storage capacitors

are connected to pins 1 and 8; whereas most op amps

leave these pins open or use them for offset null or

compensation capacitors.

The OP05 and OP07 op amps can be converted for

ICL7650/ICL7653 operation. This can be accomplished

by removing the offset null potentiometer, which is con-

nected from pins 1 and 8 to V+, and replacing it with

two capacitors connected from pins 1 and 8 to V-. For

LM108 devices, the compensation capacitor is

replaced by the external nulling capacitors. Pin 5 is the

output clamp connection on the ICL7650/ICL7653. By

removing any circuit connections from this pin, the

LM101/LM748/LM709 devices can undergo a similar

conversion.

Typical Applications

Figure 4 shows the ICL7650/ICL7653 automatically

nulling the offset voltage of a high-speed amplifier. The

ICL7650/ICL7653 continuously monitor the voltage at

the amplifier’s inverting input, integrate the error, and

drive the amplifier’s noninverting input to correct for the

offset voltage detected at the inverting input. The cir-

cuit’s DC offset characteristics are determined by the

ICL7650/ICL7653, and its AC performance is deter-

mined by the high-speed amplifier. While this circuit

continuously and automatically adjusts the amplifier’s

offset to less than 5µV, it does not correct for errors

caused by the input bias current, so the value of resis-

can be used with any op amp that is configured as an

inverting amplifier.

Figures 5 and 6 illustrate basic inverting and noninvert-

ing amplifier circuits. Both figures show an output

clamping circuit being used to enhance overload

recovery performance. Supply voltage (±8V max) and

output drive capability (10k

Ω load for full swing) are the

only limitations to consider when replacing other op

amps with the ICL7650/ICL7653. Use a simple booster

circuit to overcome these limitations (Figure 7). This

enables the full output capabilities of the LM118 (or any

other standard device) to be combined with the input

capabilities of the ICL7650/ICL7653. Observe the loop

gain stability carefully when the feedback network is

added, particularly when a slower amplifier such as the

LM741 is used.

A lower voltage supply is required when mixing the

ICL7650/ICL7653 with circuits that operate at ±15V sup-

plies. One approach is to use a highly efficient voltage

divider. This is illustrated in Figure 8, where the ICL7660

voltage converter is used to convert +15V to +7.5V.

Chopper-Stabilized Op Amps

_______________________________________________________________________________________

9

HIGH-

SPEED

AMP

0.1

µF

47

Ω

10k

100k

ICL7650

ICL7653

ICL7650

OUTPUT

(R1 || R2)

≥ 100kΩ

FOR FULL CLAMP EFFECT

INPUT

C

R

C

CLAMP

0.1

µF 0.1µF

R2

R1

1k

NOTE: R1 || R2 INDICATES THE

PARALLEL COMBINATION OF

R1 || R2.

Figure 4. Nulling a High-Speed Amplifier

Figure 5. Inverting Amplifier with Optional Clamp