LT1013 Datasheet, PDF (18/33 Pages) Linear Technology – Quad Precision Op Amp

LT1013, LT1013A, LT1013D
DUAL PRECISION OPERATIONAL AMPLIFIERS
SLOS018H − MAY 1988 − REVISED NOVEMBER 2004
APPLICATION INFORMATION
single-supply operation
The LT1013 is fully specified for single-supply operation (V_CC− = 0). The common-mode input voltage range
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
current flows from the substrate (V_CC− terminal) to the input, which can destroy the unit. On the LT1013,
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. When the input is more than 400 mV below ground (at T_A = 25°C), the input stage of similar operational
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.
5
5
5
4
4
4
3
3
3
2
1
2
2
0
1
1
−1
0
0
−2
(a) VI(PP) = −1.5 V TO 4.5 V
−1
(b) OUTPUT PHASE REVERSAL
EXHIBITED BY LM358
−1
(c) NO PHASE REVERSAL
EXHIBITED BY LT1013
Figure 24. Voltage-Follower Response With Input Exceeding
the Negative Common-Mode Input Voltage Range
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