Datasheet

LT6011/LT6012
12
60112fc
applicaTions inForMaTion
with a minimum noise of 14nV/√Hz for very low source
impedance. If the source impedance is more than 1MΩ, the
input current noise of the amplifier, multiplied by this high
impedance, starts to contribute and eventually dominate.
Total input noise spectral density can be calculated as:
v
n(TOTAL)
= e
n
2
+ 4kTR
S
+ (i
n
R
S
)
2
where e
n
= 14nV/√Hz , i
n
= 0.1pA/√Hz and R
S
is the total
impedance at the input, including the source impedance.
Capacitive Loads
The LT6011/LT6012 can drive capacitive loads up to 500pF
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 further increases the amount of capacitance that the
amplifier can drive.
Rail-to-Rail Operation
The LT6011/LT6012 outputs can swing to within millivolts
of either supply rail, but the inputs can not. However, for
most op amp configurations, the inputs need to swing
less than the outputs. Figure 1 shows the basic op amp
configurations, lists what happens to the op amp inputs
and specifies whether or not the op amp must have rail-
to-rail inputs. Select a rail-to-rail input op amp only when
really necessary, because the input precision specifications
are usually inferior.
R
G
V
REF
NONINVERTING: A
V
= 1 + R
F
/R
G
INPUTS MOVE BY AS MUCH AS
V
IN
, BUT THE OUTPUT MOVES
MORE
INPUT MAY NOT HAVE TO BE
RAIL-TO-RAIL
NONINVERTING: A
V
= 1
INPUTS MOVE BY AS MUCH AS
OUTPUT
INPUT MUST BE RAIL-TO-RAIL
FOR OVERALL CIRCUIT
RAIL-TO-RAIL PERFORMANCE
INVERTING: A
V
= –R
F
/R
G
OP AMP INPUTS DO NOT MOVE,
BUT ARE FIXED AT DC BIAS
POINT V
REF
INPUT DOES NOT HAVE TO BE
RAIL-TO-RAIL
V
IN
R
F
–
+
V
IN
V
REF
R
F
R
G
–
+
V
IN
6011 F01
–
+
Figure 1. Some Op Amp Configurations Do Not Require Rail-to-Rail Inputs to Achieve Rail-to-Rail Outputs