AD627ARZ Analog Devices Inc, AD627ARZ Datasheet - Page 15

• Manufacturer Part Number: AD627ARZ
• Description: IC AMP INST R-R 25MA 8SOIC
• Manufacturer: Analog Devices Inc
• Type: Rail-to-Railr

Specifications of AD627ARZ

• Slew Rate: 0.06 V/µs
• Amplifier Type: Instrumentation
• Number Of Circuits: 1
• Output Type: Rail-to-Rail
• -3db Bandwidth: 80kHz
• Current - Input Bias: 2nA
• Voltage - Input Offset: 25µV
• Current - Supply: 60µA
• Current - Output / Channel: 25mA
• Voltage - Supply, Single/dual (±): 2.2 V ~ 36 V, ±1.1 V ~ 18 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• No. Of Amplifiers: 1
• Input Offset Voltage: 200µV
• Gain Db Min: 5dB
• Gain Db Max: 1000dB
• Bandwidth: 40MHz
• Amplifier Output: Rail To Rail
• Cmrr: 77dB
• Supply Voltage Range: ± 1.1V To ±
• Common Mode Rejection Ratio: 90
• Current, Input Bias: 3 nA (Single), 2 nA (Dual)
• Current, Input Offset: 0.3 nA
• Current, Supply: 60 μA
• Impedance, Thermal: 155 °C/W
• Package Type: SOIC-8
• Power Dissipation: 0.8 W
• Resistance, Input: 20 Gigaohms (Differential), 20 Gigaohms (Common-Mode)
• Temperature, Operating, Range: -40 to +85 °C
• Voltage, Gain: 1000 V/V
• Voltage, Input: -35.9 to +35 V (Single), -17.9 to +17 V (Dual)
• Voltage, Input Offset: 50 μV (Single), 25 μV (Dual)
• Voltage, Noise: 38 nV/sqrt Hz
• Voltage, Supply: 2.2 to ±18 V
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Gain Bandwidth Product: -
• Lead Free Status / Rohs Status: RoHS Compliant part Electrostatic Device

RF INTERFERENCE
All instrumentation amplifiers can rectify high frequency out-of-
band signals. Once rectified, these signals appear as dc offset
errors at the output. The circuit of Figure 14 provides good RFI
suppression without reducing performance within the in amp’s
passband. Resistor R1 and capacitor C1 (and likewise, R2 and
C2) form a low pass RC filter that has a –3 dB BW equal to:
F = 1/(2 π R1C1). Using the component values shown, this
filter has a –3 dB bandwidth of approximately 8 kHz. Resistors
R1 and R2 were selected to be large enough to isolate the circuit’s
input from the capacitors, but not large enough to significantly
increase the circuit’s noise. To preserve common-mode rejec-
tion in the amplifier’s pass band, capacitors C1 and C2 need to
be 5% mica units, or low cost 20% units can be tested and
“binned” to provide closely matched devices.
Capacitor C3 is needed to maintain common-mode rejection at
the low frequencies. R1/R2 and C1/C2 form a bridge circuit
whose output appears across the in amp’s input pins. Any mis-
match between C1 and C2 will unbalance the bridge and reduce
common-mode rejection. C3 insures that any RF signals are
common mode (the same on both in amp inputs) and are not
applied differentially. This second low pass network, R1 + R2
and C3, has a –3 dB frequency equal to: 1/(2 π (R1 + R2) (C3)).
Using a C3 value of 0.022 µF as shown, the –3 dB signal BW of
this circuit is approximately 200 Hz. The typical dc offset shift
over frequency will be less than 1 mV and the circuit’s RF signal
rejection will be better than 57 dB. The 3 dB signal bandwidth
+IN
–IN
THE INPUT PINS AS POSSIBLE
LOCATE C1–C3 AS CLOSE TO
20k
20k
1%
1%
R1
R2
0.022 F
1000pF
1000pF
5%
5%
C1
C2
C3
R
G
0.33 F
0.33 F
AD627
+V
–V
S
S
0.01 F
0.01 F
AD627
REFERENCE
0.1 F
V
OUT
V
IN
POWER SUPPLY
V
5V
of this circuit may be increased by reducing the value of resistors
R1 and R2. The performance is similar to that using 20 kΩ
resistors, except that the circuitry preceding the in amp must
drive a lower impedance load.
The circuit of Figure 14 should be built using a PC board with a
ground plane on both sides. All component leads should be as
short as possible. Resistors R1 and R2 can be common 1% metal
film units but capacitors C1 and C2 need to be ± 5% tolerance
devices to avoid degrading the circuit’s common-mode rejec-
tion. Either the traditional 5% silver mica units or Panasonic
± 2% PPS film capacitors are recommended.
APPLICATIONS CIRCUITS
A Classic Bridge Circuit
Figure 15 shows the AD627 configured to amplify the signal
from a classic resistive bridge. This circuit will work in either
dual or single supply mode. Typically the bridge will be excited
by the same voltage as is used to power the in amp. Connecting
the bottom of the bridge to the negative supply of the in amp (usu-
ally either 0, –5 V, –12 V or –15 V), sets up an input common-
mode voltage that is optimally located midway between the
supply voltages. It is also appropriate to set the voltage on the
REF pin to midway between the supplies, especially if the input
signal will be bipolar. However the voltage on the REF pin can be
varied to suit the application. A good example of this is when
the REF pin is tied to the V
Converter (ADC) whose input range is (V
available output swing on the AD627 of (–V
(+V
this output range divided by the input range.
DD
ADC
0.1 F
S
– 150 mV) the maximum programmable gain is simply
AGND DGND
GND
AD7892-2
V
12
DIFF
V
DD
PROCESSOR
+V
R
–V
G
0.1 F
S
S
REF
= 200k
GAIN-5
DGND
pin of an Analog-to-Digital
AD627
0.1 F
REF
0.1 F
S
+ 100 mV) to
± V
AD627
IN
V
V
). With an
OUT
REF