LT6023-1_15 Datasheet, PDF (13/22 Pages) Linear Technology – Dual Micropower, 1.4V/s Precision Rail-to-Rail Output Amplifier

APPLICATIONS INFORMATION
LT6023/LT6023-1
V_REF
+
V_IN
+
V_IN
+
R_G
V_IN
–
R_F
–
R_F
R_G
–
60231 F02
INVERTING: A_V = –R_F/R_G
OP AMP INPUTS DO NOT MOVE,
BUT ARE FIXED AT DC BIAS
POINT V_REF
INPUT DOES NOT HAVE TO BE
RAIL-TO-RAIL
V_REF
NONINVERTING: A_V = 1 + R_F/R_G
INPUTS MOVE BY AS MUCH AS
V_IN, BUT THE OUTPUT MOVES
MORE
INPUT MAY NOT HAVE TO BE
RAIL-TO-RAIL
NONINVERTING: A_V = 1
INPUTS MOVE BY AS MUCH AS
OUTPUT
INPUT MUST BE RAIL-TO-RAIL
FOR OVERALL CIRCUIT
RAIL-TO-RAIL PERFORMANCE
Figure 2. Some Op Amp Configurations Do Not Require Rail-to-Rail Inputs to Achieve Rail-to-Rail Outputs
Achieving Rail-to-Rail Operation without
Rail-to-Rail Inputs
The LT6023 output is able to swing close to each power
supply rail, but the input stage is limited to operating
between V^– + 1.2V and V⁺ – 1.4V. For many inverting
applications and noninverting gain applications, this is
largely inconsequential. Figure 2 shows the basic op amp
configurations, what happens to the op amp inputs and
whether or not the op amp must have rail-to-rail inputs.
The circuit of Figure 3 shows an extreme example of the
inverting case. The input voltage at the 100k resistor can
swing ±13.5V and the LT6023 will output an inverted,
divided-by-ten version of the input voltage. The output
±13.5V SWINGS
WELL OUTSIDE
SUPPLY RAILS
V_IN
100k, 0.1%
1.5V
+
LT6023
–
±1.35V
OUTPUT
SWING
10k, 0.1%
–1.5V
60231 F03
Figure 3. Extreme Inverting Case: Circuit Operates Properly
with Input Voltage Swing Well Outside Op Amp Supply Rails
accuracy is limited by the resistors shown to 0.2%. Output
referred, this error becomes 2.7mV. The 30µV input offset
voltage contribution, plus the additional error due to input
bias current times the ~10k effective source impedance,
contribute only negligibly to error.
Phase Inversion
The LT6023 input stage is limited to operating between V^– +
1.2V and V⁺ – 1.4V. Exceeding this common mode range will
cause the open loop gain to drop significantly. For a unity gain
amplifier, the output roughly tracks the input well beyond
the specified input voltage range as shown in Figure 4.
20V
INPUT
V_S = ±15V
A_V = 1
10V
OUTPUT
+V_CM LIMIT
5V/DIV 0V
–10V
–V_CM LIMIT
–20V
2ms/DIV
60231 F04
Figure 4. No Phase Inversion
For more information www.linear.com/LT6023
60231fa
13