LT6023/LT6023-1

13

60231fa

For more information www.linear.com/LT6023

APPLICATIONS INFORMATION

Figure 2. Some Op Amp Configurations Do Not Require Rail-to-Rail Inputs to Achieve Rail-to-Rail Outputs

INPUTS MOVE BY AS MUCH AS

MORE

INPUT MAY NOT HAVE TO BE

RAIL-TO-RAIL

INPUTS MOVE BY AS MUCH AS

OUTPUT

INPUT MUST BE RAIL-TO-RAIL

FOR OVERALL CIRCUIT

RAIL-TO-RAIL PERFORMANCE

OP AMP INPUTS DO NOT MOVE,

BUT ARE FIXED AT DC BIAS

INPUT DOES NOT HAVE TO BE

RAIL-TO-RAIL

–

+

–

+

60231 F02

–

+

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

causetheopenloopgaintodropsignificantly.Foraunitygain

amplifier, the output roughly tracks the input well beyond

the specified input voltage range as shown in Figure 4.

Figure 4. No Phase Inversion

0V

5V/DIV

–20V

–10V

20V

10V

2ms/DIV

60231 F04

OUTPUT

INPUT

Figure 3. Extreme Inverting Case: Circuit Operates Properly

with Input Voltage Swing Well Outside Op Amp Supply Rails

1.5V

–1.5V

10k, 0.1%

100k, 0.1%

±1.35V

OUTPUT

SWING

±13.5V SWINGS

WELL OUTSIDE

SUPPLY RAILS

–

+

LT6023

60231 F03

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

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