ICL7622ACPD datasheet(21/26 Pages) MAXIM

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Detailed Description

Quiescent Current Selection

The voltage input to the IQ pin of the single and triple

amplifiers selects a quiescent current (IQ) of 10μA,

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

fixed quiescent current (IQ) settings. Unity-gain band-

width and slew-rate increase with increasing quiescent

current, as does output sink current capability. The output

source current capability is independent of quiescent

current.

The lowest IQ setting that results in sufficient bandwidth

and slew rate should be selected for each specific

application.

The IQ pin of the single and triple amplifiers controls the

quiescent current as follows:

IQ = 10μA

IQ pin to V+

IQ = 100μA

IQ pin between V- + 0.8V and V+ - 0.8V

IQ = 1mA

IQ pin to V

Input Offset Nulling

The input offset can be nulled by connecting a 25kΩ pot

between the OFFSET terminals with the wiper connected

to V+. At quiescent currents of 1mA and 100μA, the null-

ing range provided is adequate for all VOS selections.

However, with higher values of VOS, and an IQ of 10μA,

nulling may not be possible.

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 con-

nected between COMP and OUT pins, with 39pF being

greater than unity. The compensation capacitor value may

be reduced to increase the bandwidth and slew rate. The

ICL7132 is not compensated and does not have frequen-

cy compensation pins. Use only at gains 20 at IQ of 1mA;

at gains > 10 at IQ of 100μA; at gain > 5 at IQ of 10μA.

Output Loading Considerations

Approximately 70% of the amplifier’s quiescent cur-

rent 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 proportional

to load impedance, approximates a transconductance

amplifier. Approximately the same open-loop gains are

obtained at each of the IQ settings if corresponding loads

of 10kΩ, 100kΩ, and 1MΩ are used.

The maximum output source current is higher than the

maximum sink current, and is independent of IQ.

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 on the

1mA IQ setting, avoid loads less than 5kΩ. Since 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 when operated

with at least 3V total supply and an IQ of 10μA or 100μA.

The ICL7616 CMVR includes the negative supply voltage

(or ground when operated with a single supply) at an IQ

or 10μA or 100μA.

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-imped-

ance 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, conformally coated.

ICL761X–ICL764X

Single/Dual/Triple/Quad

Operational Amplifiers

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