TLC2652_17 Datasheet, PDF (22/41 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
internal/external clock
The TLC2652 has an internal clock that sets the chopping frequency to a nominal value of 450 Hz. On 8-pin
packages, the chopping frequency can only be controlled by the internal clock; however, on all 14-pin packages
and the 20-pin FK package, the device chopping frequency can be set by the internal clock or controlled
externally by use of the INT/EXT and CLK IN pins. To use the internal 450-Hz clock, no connection is necessary.
If external clocking is desired, connect INT/EXT to V_{DD −} and the external clock to CLK IN. The external clock
trip point is 2.5 V above the negative rail; however, CLK IN can be driven from the negative rail to 5 V above
the negative rail. If this level is exceeded, damage could occur to the device unless the current into CLK IN is
limited to ± 5 mA. When operating in the single-supply configuration, this feature allows the TLC2652 to be driven
directly by 5-V TTL and CMOS logic. A divide-by-
two frequency divider interfaces with CLK IN and
sets the clock chopping frequency. The duty cycle
of the external clock is not critical but should be
0
VDD _± = ± 5 V
TA = 25° C
kept between 30% and 60%.
overload recovery/output clamp
When large differential input voltage conditions
are applied to the TLC2652, the nulling loop
attempts to prevent the output from saturating by
driving C_XA and C_XB to internally-clamped voltage
levels. Once the overdrive condition is removed,
a period of time is required to allow the built-up
charge to dissipate. This time period is defined as
overload recovery time (see Figure 33). Typical
overload recovery time for the TLC2652 is
significantly faster than competitive products;
however, if required, this time can be reduced
further by use of internal clamp circuitry
accessible through CLAMP if required.
−5
0
− 50
0 10 20 30 40 50 60 70 80
t − Time − ms
Figure 33. Overload Recovery
The clamp is a switch that is automatically activated when the output is approximately 1 V from either supply
rail. When connected to the inverting input (in parallel with the closed-loop feedback resistor), the closed-loop
gain is reduced, and the TLC2652 output is prevented from going into saturation. Since the output must source
or sink current through the switch (see Figure 7), the maximum output voltage swing is slightly reduced.
thermoelectric effects
To take advantage of the extremely low offset voltage drift of the TLC2652, care must be taken to compensate
for the thermoelectric effects present when two dissimilar metals are brought into contact with each other (such
as device leads being soldered to a printed circuit board). Dissimilar metal junctions can produce thermoelectric
voltages in the range of several microvolts per degree Celsius (orders of magnitude greater than the 0.01-µV/°C
typical of the TLC2652).
To help minimize thermoelectric effects, careful attention should be paid to component selection and
circuit-board layout. Avoid the use of nonsoldered connections (such as sockets, relays, switches, etc.) in the
input signal path. Cancel thermoelectric effects by duplicating the number of components and junctions in each
device input. The use of low-thermoelectric-coefficient components, such as wire-wound resistors, is also
beneficial.
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