LT6350HMS8#TRPBF Linear Technology, LT6350HMS8#TRPBF Datasheet - Page 13

• 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

OPERATION
Notice that the output common mode voltage is determined
simply by the voltage at +IN2. However, since the voltage
applied at +IN2 does not affect the voltage at the V
a differential offset voltage will develop for V
does not equal V2. The value of the offset voltage will be
2 • (V1 – V2), as can be seen in Equation 2. For lowest
differential offset, therefore, the input signal to pin +IN1,
V
applied to pin +IN2. Often this voltage is provided by the
ADC reference output. When the input is so centered and
V1 = V2, Equation 2 reduces to:
The simple connection described in the Basic Connections
section can be seen as a special case of the general circuit
in Figure 3 where R
and the voltage at V
differential gain greater than two is needed, the values of R
and R
Additional information about feedback networks is given
in the next section and in the Input Amplifi er (Op Amp 1)
Feedback Components section.
Inverting Gain Connections/Interfacing to High
Voltage Signals
Although the previous examples have assumed the input
signal is applied at +IN1, it is also possible to use the input
op amp in an inverting confi guration by fi xing the voltage
V
input op amp in the inverting confi guration fi xes its input
common mode voltage at the voltage V
input signal at V1 to traverse a swing beyond the LT6350
supply rails. To avoid unwanted differential offsets in this
confi guration V
Then Equation (1) reduces to:
Choosing R
of –2 confi guration.
A practical application for the inverting gain confi guration is
interfacing a high voltage op amp to a 5V differential SAR
ADC. As seen in Figure 4, an industrial application might have
IN
IN
V
V
V
, should be centered around the common mode voltage
and applying the input signal at V1 of Figure 3. Using the
OUTDIFF
IN
OUTDIFF
G
= V2/(1+(R
can be adjusted in accordance with Equation (2).
F
= 2 • V
= –2 • V1 • (R
= R
IN
G
F
should be chosen such that:
A
F
/R
with the input at V1 leads to the gain
IN
is a short circuit, R
• (1+R
G
is centered around the voltage V2. If
))
F
F
/R
/R
G
G
))
)
IN
G
is an open circuit,
, which allows the
A
= 0 when V1
OUT1
output,
F
sensed signals coming through an op amp running from
±15V rails. The LT6350 can easily interface the high voltage
op amp to a 5V ADC by using the inverting gain confi guration.
For a clean interface, three conditions must be met:
1. V
2. V
3. Full-scale signals at OUT
Applying the above constraints to the design Equations
(1) to (3) gives values for the ratio of R
the value of V
SIGNAL
HIGH VOLTAGE OP AMP
R R
OUT
output of the LT6350 into the appropriate full-scale
range for the ADC.
V
I
OUTDIFF
OUT1
F
N N
+
–
/
+
R
=
HVNOM
S
V
G
IN
+15V
–15V
V
V
–IN1
A
=
Figure 4. Interfacing to High Voltage Signals
= V
2 1
(
+IN1
–
OUT
/ (
= 0 when OUT
+
–
8
1
OUT
.
OUTCM
IN
R
Figure 3. General Confi guration
V1
G
+
HV
:
MAX
(
OP AMP 1
+
–
R
+
–
R
OUT
G
F
V
−
IN
R
HVNOM
= V2 when OUT
F
/
–IN1
+IN1
OUT
R
8
1
G
OUT
OP AMP 1
)) (
HV
MIN
+
–
OUT
+
HVMAX
R
is centered at OUT
F
R
HVMIN
HV
)/(
OUT
INT
+IN2
OUT
are translated at the
R
+IN2
HVNOM
+
–
2
INT
HVMAX
V2
OP AMP 2
+
–
HV
2
–
+
R
INT
F
V2
OP AMP 2
)/(
is centered at
–
+
to R
LT6350
R
−
INT
1
OUT
V2
V2
OUT
+
OUT
(
MIN
G
HVNOM
R R
4
5
OUT
OUT
MAX
13
and for
HVMIN
G
OUT1
OUT2
6350 F03
MIN
/
MAX
4
5
6350fb
F
OUT1
OUT2
6350 F04
.
))
)