Datasheet

ICL7652
Advanced LinCMOSTM PRECISION CHOPPER-STABILIZED
OPERATIONAL AMPLIFIER
TYPICAL APPLICATION DATA
avoiding latchup
The ICL7652 inputs and output are designed to withstand -1 OO-mA surge currents without sustaining latchup.
However, because CMOS devices are susceptible to latchup due to their inherent parasitic thyristors,
techniques to reduce the chance of latchup should be used whenever possible. Internal protection diodes
should not be forward biased in normal operation. Applied input and output voltages should not exceed the
supply voltage by more than 300 mV. Care should be exercised when using capacitive coupling on pulse
generators. Supply transients should be shunted by using decoupling capacitors (0.1 ~F typical) located
across the supply rails as close to the device as possible.
The current path established if latchup occurs is usually between the supply rails and is limited only by the
impedance of the power supply and the forward resistance of the parasitic thyristor. The chance of latchup
occurring increases with increasing temperature and supply voltage.
electrostatic discharge protection
The ICL7652 incorporates internal ESD protection circuits that prevent functional failures at voltages at or
below 2000 V. Care should be exercised in handling these devices, as exposure to ESD may result in
degradation of the device parametric performance.
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theory of operation
Chopper-stabilized operational amplifiers offer the best dc performance of any monolithic operational amplifier.
This superior performance is the result of using two operational amplifiers -a main amplifier and a nulling
amplifier- plus oscillator-controlled logic and two external capacitors to create a system that behaves as a
single amplifier. With this approach, the ICL7652 achieves submicrovolt input offset voltage, submicrovolt
noise voltage, and offset voltage variations with temperature in the nV/OC range.
The ICL7652 on-chip control logic produces two dominant clock phases -a nulling phase and an amplifying
phase. The term "chopper-stabilized" derives from the process of switching between these two clock phases.
Figure 26 shows a simplified block diagram of the ICL7652. Switches A and B are make-before-break types.
During the nulling phase, switch A is closed, shorting the nulling amplifier inputs together and allowing the
nulling amplifier to reduce its own input offset voltage by feeding its output signal back to an inverting input
node. Simultaneously, external capacitor CXA stores the nulling potential to allow the offset voltage of the
amplifier to remain nulled during the amplifying phase.
During the amplifying phase, switch B is closed,
connecting the output of the nulling amplifier to a IN +
noninverting input of the main amplifier. In this
configuration, the input offset voltage of the main IN -
amplifier is nulled. Also, external capacitor CXB
stores the nulling potential to allow the offset
voltage of the main amplifier to remain nulled
during the next nulling phase.
This continuous chopping process allows offset-
voltage nulling during variations in time and .
temperature and over the common-mode input
voltage range and power supply range. In FIGURE 26. SIMPLIFIED BLOCK DIAGRAM
addition, because the low-frequency signal path
is through both the null and main amplifiers,
extremely high gain is achieved.
NULL
TEXAS .
INSTRUMENTS
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