Datasheet
2 V
PP
V
OCM
EN
100:
TWISTED PAIR
50:
2 V
PP
1000
1000
500
500
GAIN = 2
50:
a
+
-
V
I
R
G1
R
G2
V
OCM
R
L
V
O
R
F1
R
F2
C
L
R
O
R
O
EN
a
+
-
LMP8350
SNOSB80B –FEBRUARY 2011–REVISED MARCH 2013
www.ti.com
FULLY DIFFERENTIAL OPERATION
The LMP8350 will perform best when used with split supplies and in a fully differential configuration. See
Figure 30 for recommend circuits.
Figure 30. Typical Fully Differential Application
The circuit shown in Figure 30 is a typical fully differential application as might be used to drive a Sigma Delta
ADC. In this circuit, closed loop gain, is (A
V
) = V
OUT
/ V
IN
= R
F
/R
G
, where R
F
=R
F1
=R
F2
and R
G
=R
G1
=R
G2
. For all
the applications in this data sheet , V
IN
is presumed to be the voltage presented to the circuit by the signal
source. For differential signals this will be the difference of the signals on each input (which will be double the
magnitude of each individual signal), while in single ended inputs it will just be the driven input signal.
When fed with a differential signal, the LMP8350 provides excellent distortion, balance and common mode
rejection, provided the resistors R
F
, R
G
and any input termination resistors (R
T
) are well matched and strict
symmetry is observed in board layout. With a DC CMRR of over 80 dB, the DC and low frequency CMRR of
most circuits will be dominated by the external resistor matching and board trace resistance. At low distortion
levels, board layout symmetry and supply bypassing become a factor as well. It is assumed throughout this
document that R
F1
= R
F2
and R
G1
= R
G2
for maximum channel symmetry
Precision resistors of at least 0.1% accuracy or better are recommended and careful board layout will also be
required for optimum performance.
Operation with R
F
feedback resistors as low as 300 ohms is possible in the High and Medium power modes. This
will slightly improve the noise and bandwidth results. However, feedback resistors with R
F
values of less than
1KΩ should be avoided in the low power mode due to the reduced output drive current capabilities. If low value
resistors (<300Ω) must be used in the low power mode, the maximum output swing will need to be limited.
The resistors R
O
help keep the amplifier stable when presented with a load C
L
, as is common when driving an
analog to digital converter (ADC).
Figure 31. Fully Differential Cable Driver
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