LT6020/LT6020-1

13

60201fa

For more information www.linear.com/LT6020

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

–

+

–

+

60201 F02

–

+

the specified input voltage range as shown in Figure 4.

However the open loop gain is significantly reduced. While

the output roughly tracks the input, the reduction in open

loop gain degrades the accuracy of the LT6020 in this

region. Exceeding the input common mode range also

causesasignificantincreaseininputbiascurrentasshown

in Figure 5. The output of the LT6020 is guaranteed over

thespecifiedtemperaturerangenottophaseinvertaslong

as the input voltage does not exceed the supply voltage.

Preserving Input Precision

Preserving the input accuracy of the LT6020 requires

that the application circuit and PC board layout do not

Figure 4. No Phase Inversion

0V

5V/DIV

–20V

–10V

20V

10V

200µs/DIV

60201 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

–

+

LT6020

1880 F03

divided-by-ten version of the input voltage. The output

accuracy is limited by the resistors 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