LT1013, LT1013A, LT1013D

DUAL PRECISION OPERATIONAL AMPLIFIERS

SLOS018H − MAY 1988 − REVISED NOVEMBER 2004

18

POST OFFICE BOX 655303

APPLICATION INFORMATION

single-supply operation

includes ground, and the output swings to within a few millivolts of ground.

Furthermore, the LT1013 has specific circuitry that addresses the difficulties of single-supply operation, both

at the input and at the output. At the input, the driving signal can fall below 0 V, either inadvertently or on a

transient basis. If the input is more than a few hundred millivolts below ground, the LT1013 is designed to deal

with the following two problems that can occur:

1.

On many other operational amplifiers, when the input is more than a diode drop below ground, unlimited

the 400-

Ω resistors in series with the input [see schematic (each amplifier)] protect the device, even

when the input is 5 V below ground.

2.

amplifiers saturates, and phase reversal occurs at the output. This can cause lockup in servo systems.

Because of unique phase-reversal protection circuitry (Q21, Q22, Q27, and Q28), the LT1013 outputs

do not reverse, even when the inputs are at −1.5 V (see Figure 24).

This phase-reversal protection circuitry does not function when the other operational amplifier on the LT1013

is driven hard into negative saturation at the output. Phase-reversal protection does not work on amplifier 1

when amplifier 2 output is in negative saturation nor on amplifier 2 when amplifier 1 output is in negative

saturation.

At the output, other single-supply designs either cannot swing to within 600 mV of ground or cannot sink more

than a few microamperes while swinging to ground. The all-npn output stage of the LT1013 maintains its low

output resistance and high-gain characteristics until the output is saturated. In dual-supply operations, the

output stage is free of crossover distortion.

(a) VI(PP) = −1.5 V TO 4.5 V

(b) OUTPUT PHASE REVERSAL

EXHIBITED BY LM358

(c) NO PHASE REVERSAL

EXHIBITED BY LT1013

−1

0

1

2

3

4

5

−1

0

1

2

3

4

5

−1

0

1

2

3

4

5

−2

Figure 24. Voltage-Follower Response With Input Exceeding

the Negative Common-Mode Input Voltage Range