Single/Dual/Triple/Quad

Operational Amplifiers

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21

Detailed Description

Quiescent Current Selection

100µA, or 1000µA. The dual and quad amplifiers have

width and slew-rate increase with increasing quiescent

current, as does output sink current capability. The out-

put source current capability is independent of quies-

cent current.

and slew rate should be selected for each specific

application.

the quiescent current as follows:

Input Offset Nulling

The input offset can be nulled by connecting a 25kΩ

pot between the OFFSET terminals with the wiper con-

nected to V+. At quiescent currents of 1mA and 100µA,

Frequency Compensation

All of the ICL7611 and ICL7621 series except the

ICL7614 are internally compensated for unity-gain

operation. The ICL7614 is externally compensated by a

capacitor connected between COMP and OUT pins,

with 39pF being greater than unity. The compensation

capacitor value may be reduced to increase the band-

width and slew rate. The ICL7132 is not compensated

and does not have frequency compensation pins. Use

Output Loading Considerations

Approximately 70% of the amplifier’s quiescent current

flows in the output stage. The output swing can

approach the supply rails for output loads of 1MΩ,

100kΩ, and 10kΩ, using the output stage in a highly

linear Class A mode. Crossover distortion is avoided

and the voltage gain is maximized in this mode. The

output stage, however, can also be operated in Class

AB, which supplies higher output currents (see the

Typical Operating Characteristics). The voltage gain

decreases and the output transfer characteristic is non-

linear during the transition from Class A to Class B

operation.

The output stage, with a gain that is directly proportion-

al to load impedance, approximates a transconduc-

tance amplifier. Approximately the same open-loop

sponding loads of 10kΩ, 100kΩ, and 1MΩ are used.

The maximum output source current is higher than the

Like most amplifiers, there are output loads for which

the amplifier stability is not guaranteed. In particular,

avoid capacitive loads greater than 100pF; and while

the output stage is a transconductance output, very

large (>10µF) capacitive loads will create a dominant

pole and the output will be stable, even with loads that

are less than 5kΩ.

Extended Common-Mode Voltage Range

(ICL7612/ICL7616)

A common-mode voltage range that includes both V+

and V- is often desirable, especially in single-supply

operation. The ICL7612/ICL7616 extended common-

mode range op amps are designed specifically to meet

this need. The ICL7612 input common-mode voltage

range (CMVR) extends beyond both power-supply rails

of 10µA or 100µA. The ICL7616 CMVR includes the

negative supply voltage (or ground when operated with

PC Board Layout

Careful PC board layout techniques must be used to

take full advantage of the very low bias current of the

ICL7611 family. The inputs should be encircled with a

low-impedance trace, or guard, that is at the same

potential as the inputs. In an inverting amplifier, this is

normally ground; in a unity-gain buffer connect the

guard to the output. A convenient way of guarding the

8-pin TO-99 version of the ICL7611 is to use a 10-pin

circle, with the two extra pads on either side of the

input pins to provide space for a guard ring (see Figure

8). Assembled boards should be carefully cleaned,

and if a high humidity environment is expected, confor-

mally coated.