LT1352 datasheet(14/22 Pages) LINER

14 / 22 page

LT6023/LT6023-1

60231fa

For more information www.linear.com/LT6023

Figure 5. Increased Ib Beyond VICM

–1

–2

–3

–5

–10

–15

INPUT COMMON MODE VOLTAGE (V)

60231 F05

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 LT6023 in this

region. Exceeding the input common mode range also

causesasignificantincreaseininputbiascurrentasshown

in Figure 5. The output of the LT6023 is guaranteed over

thespecifiedtemperaturerangenottophaseinvertaslong

as the input voltage does not exceed the supply voltage.

Preserving Input Precision

Preserving the input accuracy of the LT6023 requires

that the application circuit and PC board layout do not

introduce errors comparable to or greater than the offset

of the amplifiers. Temperature differentials across the

input connections can generate thermocouple voltages of

tens of microvolts so the connections of the input leads

should be short, close together and away from heat dis-

sipating components. Air currents across the board can

also generate temperature differentials.

As is the case with all amplifiers, a change in load

current changes the finite open loop gain. Increased load

current reduces the open loop gain as seen in the Typical

Performance Characteristics section. This results in a

APPLICATIONS INFORMATION

changeininputoffsetvoltage.Underlargesignalconditions

with load currents of ±1mA the effective change in input

error is just tens of microvolts. In precision applications it

is important to consider amplifier loading when selecting

feedback resistor values as well as the loads on the device.

Feedback Components

Care must be taken to ensure that the phase shift formed

by the feedback resistors and the parasitic capacitance at

theinvertinginputdoesnot degradestability.Forexample,

in a gain of +2 configuration, with 1M feedback resistors

and a poorly designed circuit board layout with parasitic

capacitance of 10pF (amplifier + PC board) at the ampli-

fier’s inverting input will cause the amplifier to have poor

phase margin due to a pole formed at 32kHz. An additional

capacitor of 10pF across the feedback resistor as shown

in Figure 6 will eliminate any ringing or oscillation.

Capacitive Loads

The LT6023 can drive capacitive loads up to 100pF in

unity gain. The capacitive load driving capability increases

as the amplifier is used in higher gain configurations. A

small series resistance between the output and the load

will further increase the amount of capacitance that the

amplifier can drive.

Figure 6. Stability with Parasitic Input Capacitance

10pF

CPAR

VOUT

VIN

60231 F06

–

LT6023

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