LT1014, LT1014A, LT1014D

QUAD PRECISION OPERATIONAL AMPLIFIERS

SLOS039C – JULY 1989 – REVISED SEPTEMBER 1999

18

POST OFFICE BOX 655303

APPLICATION INFORMATION

single-supply operation

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

Furthermore, the LT1014 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 LT1014 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) 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 LT1014 outputs do

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

However, this phase-reversal protection circuitry does not function when the other operational amplifier on the

LT1014 is driven hard into negative saturation at the output. Phase-reversal protection does not work on an

amplifier:

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

than a few microproamperes while swinging to ground. The all-npn output stage of the LT1014 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 LT1014

5

4

3

2

1

0

–1

–2

5

4

3

2

1

0

–1

5

4

3

2

1

0

–1

Figure 24. Voltage-Follower Response

With Input Exceeding the Negative Common-Mode Input Voltage Range