LTC6403-1 Linear Technology, LTC6403-1 Datasheet - Page 14

• 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
Input Common Mode Voltage Range
The LTC6403-1’s input common mode voltage (V
defi ned as the average of the two input voltages, V
V
For fully differential input applications, where V
the input common mode voltage is approximately (Refer
to Figure 5):
With singled ended inputs, there is an input signal com-
ponent to the input common mode voltage. Applying only
14
V
CM
V
Figure 4. Optimal Compensation for Signal Source Impedance
V
–IN
INM
INP
V
V
+
–
–
+
. It extends from V
ICM
CM
V
V
0.01μF
VOCM
SHDN
0.1μF
•
=
V
V
⎛
⎝ ⎜
+
–
Figure 5. Circuit for Common Mode Range
V
R
R1 CHOSEN SO THAT R1 || R
R2 CHOSEN TO BALANCE R
V
+
S
F F
R
IN
+
1
2
3
4
F
SHDN
V
V
V
+
2
R
+
–
OCM
R2 = R
R
R
R
I
16
V
V
V
S
5
I
SHDN
I
+
–
⎞
⎠ ⎟
–
S
NC
NC
IN
|| R1
V
V
R1
+IN
–IN
15
≈
6
–
V
+IN
–IN
S
to 1.4V below V
INM
+
–
V
|| R1
VOCM
R
R
R
OCM
F
F
INM
= R
S
14
7
R
R
–OUT
+OUT
I
I
•
⎛
⎝ ⎜
V
V
R R
–OUTF
+OUTF
13
8
I
R
+
–
+
V
–OUTF
+OUTF
R
R
OCM
LTC6403-1
V
I
F
F
+
F
V
V
+
–
+
–
–
64031 F05
.
64031 F04
⎞
⎠ ⎟
V
V
V
V
–
+
+
–
12
11
10
+
9
INP
V
V
–OUT
+OUT
0.1μF
0.1μF
= –V
+IN
ICM
, and
INM
0.1μF
0.1μF
0.1μF
) is
V
V
V
+
–
–
,
V
approximately:
Output Common Mode Voltage Range
The output common mode voltage is defi ned as the aver-
age of the two outputs:
The V
mode feedback loop. The output common mode range
extends from 1.1V above V
pin sits in the middle of an internal voltage divider which
sets the default mid-supply open circuit potential.
In single supply applications, where the LTC6403-1 is
used to interface to an ADC, the optimal common mode
input range to the ADC is often determined by the ADC’s
reference. If the ADC makes a reference available for set-
ting the input common mode voltage, it can be directly
tied to the V
input impedance presented by the V
Electrical Characteristics Table. This impedance can be
assumed to be connected to a mid-supply potential. If an
external reference drives the V
bypassed with a high quality 0.01μF or higher capacitor to
a low impedance ground plane to fi lter any thermal noise
and to prevent common mode signals on this pin from
being inadvertently converted to differential signals.
Output Filter Considerations and Use
Filtering at the output of the LTC6403-1 is often desired
to provide either anti-aliasing or improved signal to noise
ratio. To simplify this fi ltering, the LTC6403-1 includes an
additional pair of differential outputs (+OUTF and –OUTF)
which incorporate an internal lowpass fi lter network with
a –3dB bandwidth of 44.2MHz (Figure 6).
INP
V
V
V
ICM
CM
OUTCM
(setting V
OCM
•
=
⎛
⎝ ⎜
V
R
pin sets this average by an internal common
=
+
F F
OCM
R
IN
V
+
F
INM
VOCM
+
2
R
I
pin, but must be capable of driving the
V
⎞
⎠ ⎟
to zero), the input common voltage is
–
IN
+
=
V
≈
V
INP
2
+
V
OUT
VOCM
•
–
⎛
⎝ ⎜
R
+
2
to 1V below V
OCM
F
•
V
R
⎛
⎝ ⎜
+
–
F
OUT
R R
R
pin, it should still be
I
I
R
OCM
+
⎞
⎠ ⎟
I
F
as listed in the
⎞
⎠ ⎟
+
+
. The V
64031f
OCM