LT1352 datasheet(14/20 Pages) LINER

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LT6020/LT6020-1

60201fa

For more information www.linear.com/LT6020

Figure 5. Increased Ib Beyond VICM

–10

–20

–30

–5

–10

–15

INPUT COMMON MODE VOLTAGE (V)

60201 F05

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

changeininputoffsetvoltage.Underlargesignalconditions

with load currents of ±2mA 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 pole formed by the

feedback resistors and the parasitic capacitance at the

inverting input does not degrade stability. For example, in

a gain of +2 configuration, with 100k 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

phasemarginduetoapoleformedat320kHz.Anadditional

capacitor of 10pF across the feedback resistor as shown

in Figure 6 will eliminate any ringing or oscillation.

applicaTions inForMaTion

Capacitive Loads

The LT6020 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.

Shutdown Operation (LT6020-1)

The LT6020-1 shutdown function has been designed

to be easily controlled from single supply logic or

microcontollers.ToenabletheLT6020-1whenVDGND=0V

the enable pin must be driven above 1.7V. Conversely, to

enter the low power shutdown mode the enable pin must

be driven below 0.8V. In a ±15V dual supply application

where VDGND = –15V, the enable pin must be driven above

~ –13.3V to enable the LT6020-1. If the enable pin is

driven below –14.2V the LT6020-1 enters the low power

shutdown mode. Note that to enable the LT6020-1 the

enable pin voltage can range from –13.3V to 15V whereas

to disable the LT6020-1 the enable pin can range from

–15V to –14.2V. Figure 7 shows examples of enable pin

control. While in shutdown, the outputs of the LT6020-1

are high impedance.

The LT6020-1 is typically capable of coming out of

shutdown within 100µs. This is useful in power sensitive

applications where duty cycled operation is employed

such as wireless mesh networks. In these applications the

system is in low power mode the majority of the time, but

then needs to wake up quickly and settle for an acquisition

before being powered back down to save power.

Figure 6. Stability with Parasitic Input Capacitance

100k

10pF

CPAR

VOUT

VIN

60201 F06

–

LT6020

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