LT1638 LINER [Linear Technology], LT1638 Datasheet - Page 9

• Manufacturer Part Number: LT1638
• Description: 1.2MHz, 0.4V/us Over-The-TopTM Micropower Rail-to-Rail Input and Output Op Amps
• Manufacturer: LINER [Linear Technology]

APPLICATIONS
Gain
The open-loop gain is almost independent of load when
the output is sourcing current. This optimizes perfor-
A modification of this application is shown in Figure 2
using references instead of diodes to set the maximum
slope. By using references, the slope is independent of
temperature. A scope photo shows a 1V
signal with a 2V pulse added to the sine wave; the circuit
passes the 2kHz signal but limits the slope of the pulse.
The application in Figure 3 utilizes the Over-The-Top
capabilities of the LT1638. The 0.2 resistor senses the
load current while the op amp and NPN transistor form a
closed loop making the collector current of Q1
TYPICAL APPLICATIONS
With 1.2MHz bandwidth, Over-The-Top capability, re-
verse-battery protection and rail-to-rail input and output
features, the LT1638/LT1639 are ideal candidates for
general purpose applications.
The lowpass slope limiting filter in Figure 1 limits the
maximum dV/dT (not frequency) that it passes. When the
input signal differs from the output by one forward diode
drop, D1 or D2 will turn on. With a diode on, the voltage
across R2 will be constant and a fixed current, V
will flow through capacitor C1, charging it linearly instead
of exponentially. The maximum slope that the circuit will
pass is equal to V
how fast the input changes the output will never change
any faster than the dV/dT set by the diodes and (R2)(C).
dt
dt
d
FOR R1 = 10k, R2 = 100k, C1 = 1000pF
d
V
V
OUT(MAX)
OUT(MAX)
=
= 0.006V/ s
(R2)(C1)
Figure 1. Lowpass Slope Limiting Filter
V
V
D
IN
DIODE
R1
U
R2
INFORMATION
divided by (R2)(C1). No matter
U
C1
D1
D2
U
W
–
+
1/2 LT1638
P-P
, 2kHz input
U
DIODE
1638/39 F01
V
/R2,
OUT
mance in single supply applications where the load is
returned to ground. The typical performance curve of
Open-Loop Gain for various loads shows the details.
dt
V
FOR R2 = 50k, C1 = 500pF,
MAXIMUM SLOPE = 0.048V/ s
d
IN
V
OUT
V
=
Figure 2. Lowpass Slope Limiting Filter with 0TC
OUT
V
R1
1k
(R2)(C1)
IN
1.2V
D1
100k
D3
Response of Slope Limiting Filter
R4
R2
100k
R3
C1
D2
D4
–
+
1/4 LT1639
1/4 LT1639
1/4 LT1639
LT1638/LT1639
+
–
–
+
1638/39 TA02
V
V
CC
EE
R5
100k
R6
100k
LT1634-1.2V
LT1634-1.2V
V
1638/39 F02
OUT
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