LT1784 LINER [Linear Technology], LT1784 Datasheet - Page 9

• Manufacturer Part Number: LT1784
• Description: 2.5MHz, Over-The-Top Low Power, Rail-to-Rail Input and Output Op Amp in SOT-23
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
Supply Voltage
The positive supply pin of the LT1784 should be bypassed
with a small capacitor (typically 0.1 F) within an inch of
the pin. When driving heavy loads, and additional 4.7 F
electrolytic capacitor should be used. When using split
supplies the same is true for the negative supply pin.
The LT1784 is protected against reverse battery voltages
up to 18V. In the event a reverse battery condition occurs
the supply current is less than 1nA.
Inputs
The LT1784 has two input stages, NPN and PNP (see
the Simplified Schematic), resulting in three distinct
operating regions as shown in the “Input Bias Current vs
Common Mode” Typical Performance Characteristic Curve.
For input voltages about 1V or more below V
input stage is active and the input bias current is typically
–250nA. When the input common mode voltage is within
0.6V of the positive rail, the NPN stage is operating and the
input bias current is typically 500nA. Increases in tem-
perature will cause the voltage at which operation switches
from the PNP input stage to the NPN input stage to move
towards V
untrimmed and is typically 3mV.
A Schottky diode in the collector of the input transistors,
along with special geometries for these NPN transistors,
allow the LT1784 to operate with either or both of its inputs
above V
tors is fully saturated and the input bias current is typically
200 A at room temperature. The input offset voltage is
typically 3mV when operating above V
operate with inputs 18V above V
The inputs are protected against excursions as much as
10V below V
input and a diode from the input to the negative supply.
The input stage of the LT1784 incorporates phase reversal
protection to prevent the output from phase reversing for
inputs up to 9V below V
between the inputs and the maximum differential input
voltage is 18V.
+
. At about 0.3V above V
+
. The input offset voltage of the NPN stage is
–
by an internal 1k resistor in series with each
U
–
. There are no clamping diodes
U
+
–
, the NPN input transis-
regardless of V
W
+
. The LT1784 will
+
U
, the PNP
+
.
Output
The output of the LT1784 can swing to within 80mV of the
positive rail and within 4mV of the negative rail with no
load. When monitoring input voltages within 80mV of the
positive rail or within 4mV of the negative rail, gain should
be taken to keep the output from clipping. The LT1784 can
typically sink and source over 25mA at 5V supplies,
sourcing current is reduced to 7.5mA at 3V total supplies
as noted in the electrical characteristics.
The LT1784 is internally compensated to drive at least
400pF of capacitance under any output loading condi-
tions. A 0.22 F capacitor in series with a 150 resistor
between the output and ground will compensate these
amplifiers for larger capacitive loads, up to 10,000pF at all
output currents.
Distortion
There are two main contributors to distortion in op amps:
output crossover distortion as the output transitions from
sourcing to sinking current, and distortion caused by
nonlinear common mode rejection. If the op amp is
operating inverting, there is no common mode induced
distortion. If the op amp is operating in the PNP input stage
(input not within 1V of V
typically 95dB. When the LT1784 switches between input
stages, there is significant nonlinearity in the CMRR.
Lower load resistance increases the output crossover
distortion but has no effect on the input stage transition
distortion. For lowest distortion, the LT1784 should be
operated single supply, with the output always sourcing
current and with the input voltage swing between ground
and (V
Curve, “Total Harmonic Distortion + Noise vs Output
Voltage Amplitude.”
Gain
The open-loop gain is almost independent of load when
the output is sourcing current. This optimizes perfor-
mance in single supply applications where the load is
returned to ground. The Typical Performance Characteric
Curve “Open-Loop Gain” for various loads shows the
details.
+
–1V). See Typical Performance Characteristics
+
), the CMRR is very good,
LT1784
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