TLC2652, TLC2652A, TLC2652Y

Advanced LinCMOS PRECISION CHOPPERSTABILIZED

OPERATIONAL AMPLIFIERS

SLOS019E − SEPTEMBER 1988 − REVISED FEBRUARY 2005

22

POST OFFICE BOX 655303

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.

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

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

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.

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.

0

0

10203040

t − Time − ms

0

50

60

70

80

VDD ± = ±5 V

TA = 25° C

Figure 33. Overload Recovery

−5

−50