ad8426 Analog Devices, Inc., ad8426 Datasheet - Page 16

• Manufacturer Part Number: ad8426
• Description: Wide Supply Range, Rail-to-rail Output Instrumentation Amplifier
• Manufacturer: Analog Devices, Inc.

AD8426
PRECISION STRAIN GAGE
The low offset and high CMRR over frequency of the
make it an excellent candidate for bridge measurements. The
bridge can be connected directly to the inputs of the amplifier
(see Figure 15).
DRIVING AN ADC
Figure 16 shows several different methods of driving an ADC.
The ADC in the
example because it has an unbuffered, charge sampling
architecture that is typical of most modern ADCs. This type of
architecture typically requires an RC buffer stage between the
ADC and the amplifier to work correctly.
350Ω
350Ω
350Ω
350Ω
ADuC7026
Figure 15. Precision Strain Gage
10µF
microcontroller was chosen for this
0.1µF
AD8426
AD8426
AD8426
R
+15V
–15V
3.3V
3.3V
G
+IN
–IN
5V
OPTION 1: DRIVING LOW FREQUENCY SIGNALS
OPTION 2: DRIVING HIGH FREQUENCY SIGNALS
OPTION 3: PROTECTING ADC FROM LARGE VOLTAGES
+
–
AD8426
REF
REF
REF
100Ω
10kΩ
2.5V
AD8426
AD8616
AD8616
100nF
3.3V
3.3V
Figure 16. Driving an ADC
Rev. PrD | Page 16 of 20
10Ω
10Ω
Option 1 shows the minimum configuration required to drive
a charge sampling ADC. The capacitor provides charge to the
ADC sampling capacitor, and the resistor shields the
from the capacitance. To keep the
constant of the resistor and capacitor needs to stay above 5 μs.
This circuit is mainly useful for lower frequency signals.
Option 2 shows a circuit for driving higher frequency signals.
It uses a precision op amp (AD8616) with relatively high band-
width and output drive. This amplifier can drive a resistor and
capacitor with a much higher time constant and is, therefore,
suited for higher frequency applications.
Option 3 is useful for applications where the
run off a large voltage supply, but drives a single supply ADC.
In normal operation, the
range, and the
condition, the output of the
range of both the
this circuit, because the 10 kΩ resistor between the two
amplifiers limits the current into the
10nF
10nF
AD8616
ADC0
ADC1
ADC2
ADuC7026
AD8616
AGND
AV
3.3V
Preliminary Technical Data
DD
simply buffers it. However, in a fault
AD8426
and the ADC. This is not an issue in
AD8426
AD8426
output stays within the ADC
AD8616
may go outside the supply
stable, the RC time
AD8426
to a safe level.
AD8426
needs to