5

scheme, which allows the amplifier to be set to nominal

quiescent currents of 10

µA, 100µA or 1mA. These current

settings change only very slightly over the entire supply

terminal, permitting user selection of each amplifiers’

quiescent current. The ICL7621 and ICL7641/7642 have

NOTE: The output current available is a function of the

quiescent current setting. For maximum peak-to-peak output

be selected.

Output Stage and Load Driving Considerations

Each amplifiers’ quiescent current flows primarily in the

This allows output swings to almost the supply rails for

output loads of 1M

Ω, 100kΩ, and 10kΩ, using the output

stage in a highly linear class A mode. In this mode,

crossover distortion is avoided and the voltage gain is

maximized. However, the output stage can also be operated

in Class AB for higher output currents. (See graphs under

Typical Operating Characteristics). During the transition from

Class A to Class B operation, the output transfer

characteristic is nonlinear and the voltage gain decreases.

Frequency Compensation

The ICL76XX are internally compensated, and are stable

for closed loop gains as low as unity with capacitive loads

up to 100pF.

ICL7642C only.

Output swings to within a few millivolts of the supply rails are

applications where greater common mode range is

desirable, refer to the ICL7612 data sheet.

Typical Applications

The user is cautioned that, due to extremely high input

impedances, care must be exercised in layout, construction,

board cleanliness, and supply filtering to avoid hum and

noise pickup.

chosen by the designer with regard to frequency response

and power dissipation.

FIGURE 1. SIMPLE FOLLOWER

FIGURE 2. LEVEL DETECTOR

FIGURE 3. PHOTOCURRENT INTEGRATOR

FIGURE 4. TRIANGLE/SQUARE WAVE GENERATOR

ICL76XX

+

-

ICL76XX

+

-

100k

Ω

+5

+5

1M

Ω

TO CMOS OR

LPTTL LOGIC

1

µF

ICL76XX

+

-

+

λ

NOTE: Low leakage currents allow integration times up to

several hours.

1M

Ω

+

-

1M

Ω

DUTY CYCLE

V-

V+

680k

Ω

1M

Ω

WAVEFORM GENERATOR

+

-

1/2

ICL7621

1/2

ICL7621

NOTE: Since the output range swings exactly from rail to rail, fre-

quency and duty cycle are virtually independent of power supply

variations.

ICL7621, ICL7641, ICL7642