AD8251ARMZ-RL Analog Devices Inc, AD8251ARMZ-RL Datasheet - Page 20

• Manufacturer Part Number: AD8251ARMZ-RL
• Description: IC,Instrumentation Amplifier,SINGLE,TSSOP,10PIN,PLASTIC
• Manufacturer: Analog Devices Inc
• Series: iCMOS®r

Specifications of AD8251ARMZ-RL

• Amplifier Type: Instrumentation
• Number Of Circuits: 1
• Slew Rate: 30 V/µs
• -3db Bandwidth: 10MHz
• Current - Input Bias: 5nA
• Voltage - Input Offset: 70µV
• Current - Supply: 4.1mA
• Current - Output / Channel: 37mA
• Voltage - Supply, Single/dual (±): 10 V ~ 30 V, ±5 V ~ 15 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Output Type: -
• Gain Bandwidth Product: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD8251
RF INTERFERENCE
RF rectification is often a problem when amplifiers are used in
applications where there are strong RF signals. The disturbance
can appear as a small dc offset voltage. High frequency signals
can be filtered with a low-pass RC network placed at the input
of the instrumentation amplifier, as shown in Figure 58. The
filter limits the input signal bandwidth according to the following
relationship:
where C
Values of R and C
mismatch between the R × C
R × C
By using a value of C
C
improved.
C
, the effect of the mismatch is reduced and performance is
FilterFreq
FilterFreq
C
at negative input degrades the CMRR of the AD8251.
D
≥ 10 C
R
R
DIFF
CM
C
.
C
=
should be chosen to minimize RFI. A
=
C
C
C
D
C
D
C
Figure 58. RFI Suppression
2
2
that is 10 times larger than the value of
π
π
1
RC
( R
0.1µF
0.1µF
2
C
C
+IN
–IN
C
at the positive input and the
1
D
+
AD8251
+15V
–15V
C
C
)
REF
10µF
10µF
V
OUT
Rev. B | Page 20 of 24
DRIVING AN ADC
An instrumentation amplifier is often used in front of an ADC
to provide CMRR. Usually, instrumentation amplifiers require a
buffer to drive an ADC. However, the low output noise, low
distortion, and low settle time of the AD8251 make it an
excellent ADC driver.
In Figure 59, a 1 nF capacitor and a 49.9 Ω resistor create an
antialiasing filter for the AD7612. The 1 nF capacitor stores and
delivers the necessary charge to the switched capacitor input of
the ADC. The 49.9 Ω series resistor reduces the burden of the
1 nF load from the amplifier and isolates it from the kickback
current injected from the switched capacitor input of the AD7612.
Selecting too small a resistor improves the correlation between
the voltage at the output of the AD8251 and the voltage at the
input of the AD7612 but may destabilize the AD8251. A trade-
off must be made between selecting a resistor small enough to
maintain accuracy and large enough to maintain stability.
–IN
+IN
10μF
10μF
0.1µF
0.1µF
+15V
–15V
AD8251
DGND
WR
Figure 59. Driving an ADC
A1
A0
REF
DGND
49.9Ω
1nF
0.1μF
+12V
AD7612
+5V
ADR435
–12V
0.1μF