TLC2652_17 Datasheet, PDF (23/41 Pages) Texas Instruments – Advanced LinCMOSE PRECISION CHOPPER-STABILIZED OPERATIONAL AMPLIFIERS

TLC2652, TLC2652A, TLC2652Y
Advanced LinCMOS PRECISION CHOPPERĆSTABILIZED
OPERATIONAL AMPLIFIERS
SLOS019E − SEPTEMBER 1988 − REVISED FEBRUARY 2005
APPLICATION INFORMATION
latch-up avoidance
Because CMOS devices are susceptible to latch-up due to their inherent parasitic thyristors, the TLC2652 inputs
and output are designed to withstand −100-mA surge currents without sustaining latch-up; however, techniques
to reduce the chance of latch-up should be used whenever possible. Internal protection diodes should not, by
design, be forward biased. 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 the use of decoupling capacitors (0.1 µF typical) located across the supply rails as close
to the device as possible.
The current path established if latch-up 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 latch-up
occurring increases with increasing temperature and supply voltage.
electrostatic discharge protection
The TLC2652 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.
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 TLC2652 achieves submicrovolt input offset voltage, submicrovolt noise
voltage, and offset voltage variations with temperature in the nV/°C range.
The TLC2652 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 34 shows a simplified block diagram of the TLC2652. 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 C_XA stores the nulling potential to allow the offset voltage of the amplifier to
remain nulled during the amplifying phase.
Main Amplifier
IN +
IN −
B
A
+
−
Null
Amplifier
+
−
B
CXB
A
CXA
VO
VDD _−
Figure 34. TLC2652 Simplified Block Diagram
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