TC7652 View Datasheet(PDF) - Microchip Technology

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TC7652

Low Noise, Chopper Stabilized Operational Amplifier

Microchip Technology 

TC7652

4.6 Pin Compatibility

Where possible, the 8-pin device pinout conforms to

such industry standards as the LM101 and LM741. Null

storing external capacitors connect to Pins 1 and 8,

which are usually for offset null or compensation capac-

itors. Output clamp (Pin 5) is similarly used. For OP05

and OP07 devices, replacement of the offset null

potentiometer (connected between Pins 1 and 8 and

VDD by two capacitors from those pins to VSS) provides

compatibility. Replacing the compensation capacitor

between Pins 1 and 8 by two capacitors to VSS is

required. The same operation (with the removal of any

connection to Pin 5) works for LM101, µA748 and sim-

ilar parts.

Because NC pins provide guarding between input and

other pins, the 14-pin device pinout conforms closely to

the LM108. Because this device does not use any extra

pins and does not provide offset nulling (but requires a

compensation capacitor), some layout changes are

necessary to convert to the TC7652.

4.7 Some Applications

Figures 4-2 and 4-3 show basic inverting and nonin-

verting amplifier circuits using the output clamping cir-

cuit to enhance overload recovery performance. The

only limitations on replacing other op amps with the

TC7652 are supply voltage (±8V maximum) and output

drive capability (10kΩ load for full swing). Overcome

these limitations with a booster circuit (Figure 4-4) to

combine output capabilities of the LM741 (or other

standard device) with input capabilities of the TC7652.

These two form a composite device, therefore, when

adding the feedback network, the monitor loop gains

stability.

FIGURE 4-2:

NONINVERTING

AMPLIFIER WITH

OPTIONAL CLAMP

0.1µF

Input

0.1µF

+

–

Clamp R2

TC7652

Output

R3

R1

FIGURE 4-3:

R1

Input

INVERTING AMPLIFIER

WITH OPTIONAL CLAMP

R2

Clamp

–

+

TC7652

Output

0.1µF

0.1µF

FIGURE 4-4:

USING 741 TO BOOST

OUTPUT DRIVE

CAPABILITY

TC7652

-7.5V

+

In

–

-7.5V

0.1

µF

+15V

+ 741

Out

–

-15V

0.1

µF

10kΩ

Figure 4-5 shows the clamp circuit of a zero offset com-

parator. Because the clamp circuit requires the invert-

ing input to follow the input signal, problems with a

chopper stabilized op amp are avoided. The threshold

input must tolerate the output clamp current ≈VIN/R

without disrupting other parts of the system.

Figure 4-6 shows how the TC7652 can offset null high

slew rate and wideband amplifiers.

Mixing the TC7652 with circuits operating at ±15V

requires a lower supply voltage divider with the TC7660

voltage converter circuit operated "backwards." Figure

4-7 shows an approximate connection.

FIGURE 4-5:

LOW OFFSET

COMPARATOR

0.1µF

0.1µF

VIN

+

–

Clamp

200kΩ to 2mΩ

TC7652

VOUT

VTH

DS21464B-page 8

© 2002 Microchip Technology Inc.

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