LT1678 LINER [Linear Technology], LT1678 Datasheet - Page 11

• Manufacturer Part Number: LT1678
• Description: Dual/Quad Low Noise, Rail-to-Rail, Precision Op Amps
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
Unity-Gain Buffer Application
When R
signal pulse (>1V), the output waveform will look as
shown in the pulsed operation diagram (Figure 2).
During the fast feedthrough-like portion of the output, the
input protection diodes effectively short the output to the
Rail-to-Rail Operation
To take full advantage of an input range that can exceed
the supply, the LT1678/LT1679 are designed to eliminate
phase reversal. Referring to the photographs shown in
Figure 1, the LT1678/LT1679 are operating in the fol-
lower mode (A
of the LT1678/LT1679 clips cleanly and recovers with no
phase reversal. This has the benefit of preventing lock-up
in servo systems and minimizing distortion components.
Figure 1. Voltage Follower with Input Exceeding the Supply
–0.5
–0.5
F
≤ 100Ω and the input is driven with a fast, large-
3
2
1
0
3
2
1
0
V
= +1) at a single 3V supply. The output
Input = –0.5V to 3.5V
U
Voltage (V
LT1678 Output
U
50µs/DIV
50µs/DIV
S
= 3V)
W
16789 F01b
16789 F01a
U
input and a current, limited only by the output short-circuit
protection, will be drawn by the signal generator. With
R
requirements (I
in its active mode and a smooth transition will occur.
As with all operational amplifiers when R
be created with R
creating additional phase shift and reducing the phase
margin. A small capacitor (20pF to 50pF) in parallel with R
will eliminate this problem.
Noise Testing
The 0.1Hz to 10Hz peak-to-peak noise of the LT1678/
LT1679 are measured in the test circuit shown (Figure 3).
The frequency response of this noise tester (Figure 4)
indicates that the 0.1Hz corner is defined by only one zero.
The test time to measure 0.1Hz to 10Hz noise should not
exceed ten seconds, as this time limit acts as an additional
zero to eliminate noise contributions from the frequency
band below 0.1Hz.
Measuring the typical 90nV peak-to-peak noise perfor-
mance of the LT1678/LT1679 requires special test pre-
cautions:
1. The device should be warmed up for at least five
2. For similar reasons, the device must be well shielded
F
minutes. As the op amp warms up, its offset voltage
changes typically 3µV due to its chip temperature
increasing 10°C to 20°C from the moment the power
supplies are turned on. In the ten-second measurement
interval these temperature-induced effects can easily
exceed tens of nanovolts.
from air currents to eliminate the possibility of
thermoelectric effects in excess of a few nanovolts,
which would invalidate the measurements.
≥ 500Ω, the output is capable of handling the current
+
–
R
F
LT1678
L
Figure 2. Pulsed Operation
≤ 20mA at 10V) and the amplifier stays
F
and the amplifier’s input capacitance,
OUTPUT
LT1678/LT1679
F
> 2k, a pole will
sn16789 16789fs
6V/µs
11
16789 F02
F