LTC6403-1 Linear Technology, LTC6403-1 Datasheet - Page 12

• Manufacturer Part Number: LTC6403-1
• Description: Low Power Fully Differential Input/Output Amplifier/Driver
• Manufacturer: Linear Technology

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APPLICATIONS INFORMATION
LTC6403-1
the non-linear capacitance, the outputs still have the ability
to sink and source small amounts of transient current if
exposed to signifi cant voltage transients. The inputs (+IN
and –IN) appear as anti-parallel diodes which can conduct
if voltage transients at the input exceed 1.4V. The inputs
also have steering diodes to either supply. The turn-on
time between the shutdown and active states is typically
4μs, and turn-off time is typically 350ns.
General Amplifi er Applications
As levels of integration have increased and correspond-
ingly, system supply voltages decreased, there has been
a need for ADCs to process signals differentially in order
to maintain good signal to noise ratios. These ADCs are
typically operated from a single supply voltage which can
be as low as 3V (2.7V min), and will have an optimal com-
mon mode input range near mid-supply. The LTC6403-1
makes interfacing to these ADCs trivial, by providing both
single ended to differential conversion as well as common
mode level shifting. The front page of this datasheet shows
a typical application. Referring to Figure 1, the gain to
V
Note from the above equation, the differential output
voltage (V
input and output common mode voltages. This makes
the LTC6403-1 ideally suited for pre-amplifi cation, level
shifting and conversion of single-ended input signals to
differential output signals in preparation for driving dif-
ferential input ADCs.
Effects of Resistor Pair Mismatch
Figure 3 shows a circuit diagram with takes into consid-
eration that real world resistors will not perfectly match.
Assuming infi nite open loop gain, the differential output
relationship is given by the equation:
12
OUTDIFF
V
OUTDIFF
from V
+OUT
=
V
+
INM
– V
OUT
–OUT
and V
–
V
–
) is completely independent of
OUT
INP
is:
≈
R
R
F
I
•
(
V
INP
–
V
INM
)
where:
R
of R
β
from the outputs to their respective inputs:
Δβ is defi ned as the difference in feedback factors:
V
V
mon mode voltage):
and V
voltages:
V
V
AVG
INCM
INP
F
INM
INP
V
β
V
Δ =
V
β
is the average of R
Figure 3. Real-World Application with Feedback Resistor
Pair Mismatch
+
–
–
+
, and V
INDIFF
I1
INCM
OUTDIFF
Δ
AVG
β
AVG
is defi ned as the average feedback factor (or gain)
, and R
V
V
β
INDIFF
0.01μF
is defi ned as the average of the two input voltages
VOCM
SHDN
0.1μF
V
V
+
–
R
=
•
=
= V
I
V
INM
2
2
1
2
I
R
1
=
N N CM
+
I2
•
is defi ned as the difference of the input
I
INP
•
1
2
3
4
2
⎛
⎝ ⎜
V
R
SHDN
V
V
V
.
(also called the source-referred input com-
(
+
–
OCM
+
R
F
V
R
R
16
V
V
OUT
2
I2
I1
–
INP
– V
5
I
SHDN
+
–
1
R
NC
NC
β
–
+
I
V
V
Δβ
INM
AVG
1
R
+
+IN
–IN
R
–
15
6
F1
F
I
1
V
V
1
R
INM
+IN
–IN
+
, and R
–
+
–
V
•
+
I
R
R
OUT
OCM
1
R
F2
F1
V
R
OCM
F
)
I
1
2
14
7
≈
R
+
–OUT
+OUT
I
R
F2
2
R
R
F
I
, and R
V
V
F
–OUTF
+OUTF
13
2
8
•
⎞
⎠ ⎟
V
–OUTF
+OUTF
LTC6403-1
INDIFF
V
+
V
V
–
–
64031 F03
I
V
V
V
V
is the average
–
+
+
–
12
11
10
9
+
V
V
–OUT
+OUT
0.1μF
0.1μF
0.1μF
0.1μF
0.1μF
64031f
V
V
V
+
–
–