AD8476 AD [Analog Devices], AD8476 Datasheet - Page 19

• Manufacturer Part Number: AD8476
• Description: Low Power, Unity Gain, Fully
• Manufacturer: AD [Analog Devices]

Data Sheet
APPLICATIONS INFORMATION
TYPICAL CONFIGURATION
The
conversion, common-mode level shifting, and precision processing
of signals so that they are compatible with low voltage ADCs.
Figure 54 shows a typical connection diagram of the AD8476.
SINGLE-ENDED-TO-DIFFERENTIAL CONVERSION
Many industrial systems have single-ended inputs from input
sensors; however, the signals are frequently processed by high
performance differential input ADCs for higher precision. The
AD8476
single-ended signals to the differential inputs of precision
ADCs, and it does so with no need for external components.
To convert a single-ended signal to a differential signal, connect
one input to the signal source and the other input to ground (see
Figure 54). Note that either input can be driven by the source
with the only effect being that the outputs have reversed polarity.
The
precision systems with differential signal paths.
SETTING THE OUTPUT COMMON-MODE VOLTAGE
The VOCM pin of the
precision voltage divider comprising of two 1 MΩ resistors
between the supplies. This divider level shifts the output to
midsupply. Relying on the internal bias results in an output
common-mode voltage that is within 0.05% of the expected
value.
SOURCE
SIGNAL
AD8476
AD8476
INPUT
performs the critical function of precisely converting
Figure 54. Typical Configuration—8-Lead MSOP
is designed to facilitate single-ended-to-differential
also accepts truly differential input signals in
10kΩ
10kΩ
AD8476
–5V
+5V
0.1µF
0.1µF
AD8476
is internally biased by a
10kΩ
10kΩ
LOAD
–V
+V
OUT
OUT
Rev. B | Page 19 of 24
In cases where control of the output common-mode level is
desired, an external source or resistor divider can be used to
drive the VOCM pin. If driven directly from a source, or with a
resistor divider of unequal resistor values, the resistance seen by
the VOCM pin should be less than 1 kΩ. If an external voltage
divider consisting of equal resistor values is used to set VOCM
to midsupply, higher values can be used because the external
resistors are placed in parallel with the internal resistors. The
output common-mode offset listed in the Specifications section
assumes that the VOCM input is driven by a low impedance
voltage source.
Because of the internal divider, the VOCM pin sources and sinks
current, depending on the externally applied voltage and its
associated source resistance.
It is also possible to connect the VOCM input to the common-
mode level output of an ADC; however, care must be taken to
ensure that the output has sufficient drive capability. The input
impedance of the VOCM pin is 500 kΩ. If multiple
devices share one ADC reference output, a buffer may be neces-
sary to drive the parallel inputs.
Table 6. Differential Input ADCs
ADC
1
AD7674
AD7684
AD7687
AD7688
Depending on measurement/application type, check that the AD8476 meets
settling time requirements.
Resolution Throughput Rate Power Dissipation
16 Bits
16 Bits
16 Bits
16 Bits
100 kSPS
100 kSPS
250 kSPS
500 kSPS*
1
25 mW
6 mW
12.5 mW
21.5 mW
AD8476
AD8476