Datasheet
AD8226 Data Sheet
Rev. C | Page 24 of 28
PRECISION STRAIN GAGE
The low offset and high CMRR over frequency of the AD8226
make it an excellent candidate for performing bridge measure-
ments. The bridge can be connected directly to the inputs of the
amplifier (see Figure 65).
5V
2.5V
10µF 0.1µF
AD8226
+IN
–IN
R
G
350Ω
350Ω350Ω
350Ω
+
–
07036-010
Figure 65. Precision Strain Gage
DRIVING AN ADC
Figure 66 shows several methods for driving an ADC. The
ADuC7026 microcontroller was chosen for this example because it
contains ADCs with 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
amplifier to work correctly.
Option 1 shows the minimum configuration required to drive
a charge-sampling ADC. The capacitor provides charge to the
ADC sampling capacitor while the resistor shields the AD8226
from the capacitance. To keep the AD8226 stable, the RC time
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 speed signals. It uses a
precision op amp (AD8616) with relatively high bandwidth 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 AD8226 needs to
run off a large voltage supply but drive a single-supply ADC.
In normal operation, the AD8226 output stays within the ADC
range, and the AD8616 simply buffers it. However, in a fault
condition, the output of the AD8226 may go outside the supply
range of both the AD8616 and the ADC. This is not an issue in
the circuit, however, because the 10 kΩ resistor between the two
amplifiers limits the current into the AD8616 to a safe level.
AD8226
REF
100nF
100Ω
10kΩ
10Ω
10nF
ADC0
ADC1
ADC2
AGND
3.3V
3.3V
3.3V
OPTION 1: DRIVING LOW FREQUENCY SIGNALS
OPTION 2: DRIVING HIGH FREQUENCY SIGNALS
OPTION 3: PROTECTINGADC FROM LARGE VOLTAGES
3.3V
AD8226
AD8616
ADuC7026
REF
3.3V
10Ω
10nF
AD8226
AD8616
REF
+15V
–15V
AV
DD
07036-065
Figure 66. Driving an ADC