LT6 020/LT6020-1
14
60201fa
For more information www.linear.com/LT6020
Figure 5. Increased Ib Beyond VICM
70
60
50
40
30
20
10
0
–10
–20
–30
0 5–5–10–15 10 15
INPUT COMMON MODE VOLTAGE (V)
INPUT BIAS CURRENT (µA)
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
change in input offset voltage. Under large signal conditions
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
phase margin due to a pole formed at 320kHz. An additional
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. To enable the LT6020-1 when V
DGND
= 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 V
DGND
= –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
100k
10pF
C
PAR
V
OUT
V
IN 60201 F06
+
–
LT6020
