AD627BR Analog Devices Inc, AD627BR Datasheet - Page 14

• Manufacturer Part Number: AD627BR
• Description: IC AMP INST R-R 25MA 8SOIC
• Manufacturer: Analog Devices Inc

Specifications of AD627BR

• Slew Rate: 0.06 V/µs
• Mounting Type: Surface Mount
• Rohs Status: RoHS non-compliant
• 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
• Package / Case: 8-SOIC (3.9mm Width)
• No. Of Amplifiers: 1
• Bandwidth: 80kHz
• Amplifier Case Style: SOIC
• No. Of Pins: 8
• Single Supply Voltage Min (+v): 1.1V
• Programmable Gain Max: 1000
• Gain Bandwidth Product: -
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

AD627
THEORY OF OPERATION
The AD627 is a true instrumentation amplifier, built using two
feedback loops. Its general properties are similar to those of the
classic two-op-amp instrumentation amplifier configuration but
internally the details are somewhat different. The AD627 uses a
modified current feedback scheme, which, coupled with interstage
feedforward frequency compensation, results in a much better
common-mode rejection ratio (CMRR) at frequencies above
dc (notably the line frequency of 50 Hz to 60 Hz) than might
otherwise be expected of a low power instrumentation amplifier.
In Figure 35, A1 completes a feedback loop that, in conjunction
with V1 and R5, forces a constant collector current in Q1. Assume
that the gain-setting resistor (R
and R1 complete the loop and force the output of A1 to be equal
to the voltage on the inverting terminal with a gain of nearly
1.25. A2 completes a nearly identical feedback loop that forces
a current in Q2 that is nearly identical to that in Q1; A2 also
provides the output voltage. When both loops are balanced, the
gain from the noninverting terminal to V
whereas the gain from the output of A1 to V
G
) is not present. Resistors R2
REF
–IN
2kΩ
OUT
100kΩ
R1
OUT
+V
–V
is equal to 5,
S
S
is equal to −4.
EXTERNAL GAIN RESISTOR
Figure 35. Simplified Schematic
Q1
R5
200kΩ
Rev. D | Page 14 of 24
25kΩ
R2
A1
V1
R
G
25kΩ
0.1V
R3
The inverting terminal gain of A1 (1.25) times the gain of A2
(−4) makes the gain from the inverting and noninverting
terminals equal.
The differential mode gain is equal to 1 + R4/R3, nominally 5,
and is factory trimmed to 0.01% final accuracy. Adding an
external gain setting resistor (R
amount equal to (R4 + R1)/R
AD627 is given by
Laser trims are performed on R1 through R4 to ensure that
their values are as close as possible to the absolute values in the
gain equation. This ensures low gain error and high common-
mode rejection at all practical gains.
Q2
R6
200kΩ
–V
V
+V
OUT
S
S
A2
100kΩ
2kΩ
R4
= [V
+IN
IN
(+) – V
OUTPUT
IN
(−)] × (5 + 200 kΩ/R
G
. The output voltage of the
G
) increases the gain by an
G
) + V
REF
(1)