LT6350HMS8#TRPBF Linear Technology, LT6350HMS8#TRPBF Datasheet - Page 19

• Manufacturer Part Number: LT6350HMS8#TRPBF
• Description: IC DIFF CONVERT/ADC DRIVER 8MSOP
• Manufacturer: Linear Technology
• Type: ADC Driverr

Specifications of LT6350HMS8#TRPBF

• Applications: Data Acquisition
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS INFORMATION
Because the input bias current into op amp 2 is much larger
than the offset current, choosing R
reduces the offset contribution of op amp 2’s input currents
on all units. With R
VOS
installed at +IN2.
The value of V
Because linear modulation of V
mode could degrade the common mode rejection ratio
specifi cation of op amp 1, and nonlinear modulation of
V
is trimmed to a low constant value over as wide an input
common mode range as possible. A precision, 2-point
trim algorithm is used that results in V
over the input range V
within ±300μV over the input range V
negative supply below –1.3V can be used to extend the
input range for which V
down to ground.
As a result of the trim procedure, the lowest offsets, both
common mode and differential mode, will occur with a
499Ω resistor at +IN2. This resistor can be bypassed with
a capacitor to eliminate its noise contribution. The gain-
setting resistor network (R
be matched to that of the source to minimize op amp 1’s
input bias current contributions to the offsets.
NOISE CONSIDERATIONS
A model showing the sources of output noise in the LT6350
is shown in Figure 8. The total output noise resulting from
all contributors is governed by the equation:
OS1
VOS
e
2e
no
CM
2
could cause nonlinear gain error (distortion), V
nRINT
= √(4 • [e
CM
is trimmed to within ±125μV with a 499Ω resistor
= VOS2 – (IOS2/2) • R
+ (i
OS1
n2
2
n1
R
is trimmed to bring V
INT
+IN2
+ (i
)
2
n1
–
= R
OS1
+ 4 • (i
R
+ 1.3V ≤ V
S
INT
G
)
is within ±125μV all the way
2
and R
/2, VOS
+ e
n2
OS1
INT
R
2
+IN2
nRS
+IN2
F
) impedance should
with input common
+IN1
CM
to be R
](1 + (R
OS1
)
OSDIFF
–
2
≤ V
)
reduces to:
≤ V
within ±125μV
+IN1
INT
+
to ± 125μV.
F
/ R
and V
/2 greatly
≤ V
G
))
2
+
OS1
OS1
. A
+ 4 • (i
Note that the parallel combination of gain-setting resis-
tors R
from the point of view of noise calculations, and the value
should be kept below about 1k to avoid increasing the
output noise. Lower-value gain and feedback resistors,
The LT6350 uses very low noise op amps, resulting in a
total differential output spot noise at 10kHz of 8.2nV/√Hz
when the LT6350 is in the noninverting gain-of-two con-
fi guration shown in Figure 2. This is equivalent to the
voltage noise of a 1015Ω resistor at the +IN1 input. For
source resistors larger than about 1k, voltage noise due to
the source resistance will start to dominate output noise.
Source resistors larger than about 13k will interact with
the input current noise and result in output noise that is
resistor noise and amplifi er current noise dominant.
n1
R
+IN1
F
)
2
F
R
e
+ 4e
S
–IN1
nRS
and R
e
n1
2
nRF
R
e
G
nRF
e
G
nRG
OP AMP 1
behaves like the source resistance, R
(1 + (R
i
i
n1
+
–
n1
R
Figure 8. Noise Model
F
F
R
/ R
+IN2
INT
G
R
e
)) + 4e
+IN2
e
nR+IN2
nRINT
e
n2
2
e
nRINT
n2
i
OP AMP 2
i
n2
n2
+ 4e
–
+
R
INT
LT6350
2
nR+IN2
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e
+
–
e
no
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no2
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