LT1352 datasheet(12/22 Pages) LINER

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LT6023/LT6023-1

60231fa

For more information www.linear.com/LT6023

APPLICATIONS INFORMATION

Figure 1. Settling Time Is Essentially Flat

will lower the slew rate to 0.02V/µs. Note that for these

smaller inputs the LT6023 slew rate approaches the slew

rate more common in traditional micropower amplifiers.

Input Bias Current

The design of the input stage of the LT6023 is more so-

phisticated than that shown in the Simplified Schematic.

It uses both NPN and PNP input differential amplifiers to

sense the input differential voltage. As a result the speci-

fied input bias current may flow in or out of the input pins.

Multiplexer Applications/High Dynamic Input

Impedance

The LT6023 has features which make it desirable for

multiplexer applications, such as the application featured

on the front page of this data sheet. When the channels of

the multiplexer are cycled, the output of the multiplexer

can produce large voltage transitions. Normally, bipolar

amplifiers have back-to-back diodes between the inputs,

whichwillturnonwhentheinputtransientvoltageexceeds

0.7V, causing a large transient current to be conducted

from the amplifier output stage back into the input driving

circuitry. The driving circuitry then needs to absorb this

current and settle before the amplifier can settle. The

LT6023 uses 5.5V Zener diodes to protect its inputs which

dramaticallyincreasesitsinputimpedancewithinputsteps

as large as 5V.

OUTPUT STEP (VP-P)

200

150

100

60231 F01

AV = 1

0.01%

0.0015%

Preserving Low Power Operation

The proprietary circuitry used in the LT6023 provides an

excellent combination of low power, low offset and en-

hancedslewrate.Normallyanamplifierwithhighersupply

current would be required to achieve this combination of

slew rate and precision. Special care must be taken to

ensure that the low power operation is preserved.

The choice of feedback resistor values impacts several

op-amp parameters as noted in the feedback compo-

nents section. It should also be noted that the output of

the amplifier must drive this network. For example, in a

gain of two with a total feedback resistance of 10kΩ and

an output voltage of 14V, the amplifier’s output will need

to supply 1.4mA of current. This current will ultimately

come from a supply.

The supply current of the LT6023 increases with large

differential input voltages. Normally, this does not impact

the low power nature of the LT6023 because the ampli-

fier is forcing the two inputs to be at the same potential.

Conditionswhichcausedifferentialinputvoltagetoappear

should be avoided in order to preserve the low power dis-

sipation of the LT6023. This includes but is not limited

to: operation as a comparator, excessive loading on the

output and overdriving the input.

Enhanced Slew Rate

The LT6023 uses a proprietary input stage which provides

an enhanced slew rate without sacrificing input precision

specssuchasinputoffsetvoltage,commonmoderejection

and noise. The unique input stage of the LT6023 allows the

output to quickly slew to its final value when large signal

input steps are applied. This enhanced slew characteristic

allows the LT6023 to quickly settle the output to 0.0015%

independentofinputstepsizeasshowninFigure1.Typical

micropoweramplifierscannotprocesslargeamplitudesig-

nals with this speed. As shown in the Typical Performance

curves, when the LT6023 is configured in unity gain and

a 10V step is applied to the input the output will slew at

1.4V/µs. In this same configuration, a 5V input step will

slewtheoutputat0.65V/µs.Furthermore,a0.7Vinputstep

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