AD8227BRMZ-RL Analog Devices Inc, AD8227BRMZ-RL Datasheet - Page 20

• Manufacturer Part Number: AD8227BRMZ-RL
• Description: LowCostWideInputRangeInAmp G-5
• Manufacturer: Analog Devices Inc

Specifications of AD8227BRMZ-RL

• Amplifier Type: Instrumentation
• Number Of Circuits: 1
• Output Type: Rail-to-Rail
• Slew Rate: 0.8 V/µs
• -3db Bandwidth: 250kHz
• Current - Input Bias: 20nA
• Voltage - Input Offset: 100µV
• Current - Supply: 350µA
• Current - Output / Channel: 13mA
• Voltage - Supply, Single/dual (±): 2.2 V ~ 36 V, ±1.5 V ~ 18 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Gain Bandwidth Product: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD8227
REFERENCE TERMINAL
The output voltage of the AD8227 is developed with respect to
the potential on the reference terminal. This is useful when the
output signal needs to be offset to a precise midsupply level. For
example, a voltage source can be tied to the REF pin to level-
shift the output so that the AD8227 can drive a single-supply
ADC. The REF pin is protected with ESD diodes and should
not exceed either +V
For best performance, source impedance to the REF terminal
should be kept below 2 Ω. As shown in Figure 58, the reference
terminal, REF, is at one end of a 50 kΩ resistor. Additional imped-
ance at the REF terminal adds to this 50 kΩ resistor and results
in amplification of the signal connected to the positive input.
The amplification from the additional R
follows:
Only the positive signal path is amplified; the negative path
is unaffected. This uneven amplification degrades CMRR.
INPUT VOLTAGE RANGE
Most instrumentation amplifiers have a very limited output
voltage swing when the common-mode voltage is near the
upper or lower limit of the part’s input range. The AD8227 has
very little of this limitation. See Figure 9 through Figure 16 for
the input common-mode range vs. output voltage of the part.
LAYOUT
To ensure optimum performance of the AD8227 at the PCB
level, care must be taken in the design of the board layout. The
pins of the AD8227 are arranged in a logical manner to aid in
this task.
6(50 kΩ + R
V
INCORRECT
AD8227
REF
Figure 59. Driving the Reference Pin
REF
)/(60 kΩ + R
–IN
+IN
R
R
S
G
G
Figure 60. Pinout Diagram
or −V
1
2
3
4
(Not to Scale)
AD8227
TOP VIEW
S
by more than 0.3 V.
REF
V
)
OP1177
+
–
8
7
6
5
CORRECT
+V
V
REF
–V
OUT
REF
S
S
AD8227
can be calculated as
REF
Rev. 0 | Page 20 of 24
Common-Mode Rejection Ratio over Frequency
Poor layout can cause some of the common-mode signals to be
converted to differential signals before reaching the in-amp.
Such conversions occur when one input path has a frequency
response that is different from the other. To keep CMRR over
frequency high, the input source impedance and capacitance of
each path should be closely matched. Additional source resis-
tance in the input path (for example, for input protection) should
be placed close to the in-amp inputs, which minimizes the
interaction of the source resistance with parasitic capacitance
from the PCB traces.
Parasitic capacitance at the gain setting pins can also affect CMRR
over frequency. If the board design has a component at the gain
setting pins (for example, a switch or jumper), the component
should be chosen so that the parasitic capacitance is as small as
possible.
Power Supplies
A stable dc voltage should be used to power the instrumentation
amplifier. Noise on the supply pins can adversely affect perfor-
mance. See the PSRR performance curves in Figure 23 and
Figure 24 for more information.
A 0.1 μF capacitor should be placed as close as possible to each
supply pin. As shown in Figure 61, a 10 μF tantalum capacitor
can be used farther away from the part. In most cases, it can be
shared by other precision integrated circuits.
References
The output voltage of the AD8227 is developed with respect to
the potential on the reference terminal. Care should be taken to
tie REF to the appropriate local ground.
Figure 61. Supply Decoupling, REF, and Output Referred to Local Ground
R
G
+IN
–IN
AD8227
+V
–V
S
S
0.1µF
0.1µF
REF
10µF
10µF
LOAD
V
OUT