ICL7621

FN3403 Rev.5.00

Page 4 of 9

Mar 4, 2010

Application Information

Static Protection

All devices are static protected by the use of input diodes.

However, strong static fields should be avoided, as it is

possible for the strong fields to cause degraded diode junction

characteristics, which may result in increased input leakage

currents.

Latchup Avoidance

Junction-isolated CMOS circuits employ configurations which

produce a parasitic 4-layer (PNPN) structure. The 4-layer

structure has characteristics similar to an SCR, and under

certain circumstances may be triggered into a low impedance

state resulting in excessive supply current. To avoid this

condition, no voltage greater than 0.3V beyond the supply rails

may be applied to any pin. In general, the op amp supplies

must be established simultaneously with, or before any input

signals are applied. If this is not possible, the drive circuits

must limit input current flow to 2mA to prevent latchup.

which allows the amplifier to be set to nominal quiescent currents

of 10µA, 100µA or 1mA. These current settings change only very

slightly over the entire supply voltage range. The ICL7611/12

setting of 100µA.

Output Stage and Load Driving Considerations

Each amplifiers’ quiescent current flows primarily in the output

output swings to almost the supply rails for output loads of

1M

, 100k, and 10k, 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 in “Typical Performance Curves”

beginning on page 6). 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.

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.

FIGURE 1. SIMPLE FOLLOWER

FIGURE 2. LEVEL DETECTOR

FIGURE 3. PHOTOCURRENT INTEGRATOR

FIGURE 4. TRIANGLE/SQUARE WAVE GENERATOR

ICL76XX

+

-

ICL76XX

+

-

100k



+5

+5

1M



TO CMOS OR

LPTTL LOGIC

1µF

ICL76XX

+

-

+



NOTE: Low leakage currents allow integration times up to

several hours.

1M



+

-

1M



DUTY CYCLE

V-

V+

680k



1M



WAVEFORM GENERATOR

+

-

1/2

ICL7621

1/2

ICL7621

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

frequency and duty cycle are virtually independent of power supply

variations.