AD627AR Analog Devices Inc, AD627AR Datasheet - Page 18

• Manufacturer Part Number: AD627AR
• Description: IC AMP INST R-R 25MA 8SOIC
• Manufacturer: Analog Devices Inc

Specifications of AD627AR

• 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
• Amplifier Case Style: SOIC
• No. Of Pins: 8
• Programmable Gain Max: 1000
• Supply Voltage Min: 2.2V
• Gain Min, V/v: 5
• Gain Max, V/v: 1000
• Gain Bandwidth Product: -
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

AD627
MAKE vs. BUY: A TYPICAL APPLICATION ERROR
BUDGET
The example in Figure 41 serves as a good comparison between
the errors associated with an integrated and a discrete in-amp
implementation. A ±100 mV signal from a resistive bridge
(common-mode voltage = 2.5 V) is amplified. This example
compares the resulting errors from a discrete two-op-amp
instrumentation amplifier and the AD627. The discrete
implementation uses a four-resistor precision network
(1% match, 50 ppm/°C tracking).
Table 9. Make vs. Buy Error Budget
Error Source
ABSOLUTE ACCURACY at T
DRIFT TO 85°C
Total RTI Offset Voltage, mV
Input Offset Current, nA
Internal Offset Current
(Homebrew Only)
CMRR, dB
Gain
Gain Drift, ppm/°C
Total RTI Offset Voltage, mV/°C
Input Offset Current, pA/°C
350Ω
350Ω
+5V
A
= 25°C
350Ω
350Ω
±100mV
AD627 Circuit Calculation
(250 μV + (1000 μV/10))/100 mV
1 nA × 350 Ω/100 mV
Not applicable
77 dB→141 ppm × 2.5 V/100 mV
0.35% + 0.1%
(−75 + 10) ppm/°C × 60°C
(3.0 μV/°C + (10 μV/°C/10)) ×
60°C/100 mV
(16 pA/°C × 350 Ω × 60°C)/100 mV
AD627A GAIN = 9.98 (5+(200kΩ/R
+10ppm/°C
40.2kΩ
R
1%
G
+5V
AD627A
Figure 41. Make vs. Buy
Rev. D | Page 18 of 24
G
))
+2.5V
V
OUT
Homebrew Circuit Calculation
(180 μV × 2)/100 mV
20 nA × 350 Ω/100 mV
0.7 nA × 350 Ω/100 mV
(1% match × 2.5 V)/10/100 mV
1% match
Total Absolute Error
50 ppm/°C × 60°C
(2 × 3.5 μV/°C × 60°C)/100 mV
(33 pA/°C × 350 Ω × 60°C)/100 mV
Total Drift Error
Grand Total Error
+2.5V
The errors associated with each implementation (see Table 9)
show the integrated in-amp to be more precise at both ambient
and overtemperature. Note that the discrete implementation is
more expensive, primarily due to the relatively high cost of the
low drift precision resistor network.
The input offset current of the discrete instrumentation amplifier
implementation is the difference in the bias currents of the two-
op amplifiers, not the offset currents of the individual op amps.
In addition, although the values of the resistor network are chosen
so that the inverting and noninverting inputs of each op amp
see the same impedance (about 350 Ω), the offset current of
each op amp adds another error that must be characterized.
3.15kΩ*
*1% RESISTOR MATCH, 50ppm/°C TRACKING
HOMEBREW IN-AMP, G = +10
350Ω*
1/2
LT10781SB
350Ω*
3.15kΩ*
1/2
+5V
LT10781SB
27,039
Total Error
AD627
(ppm)
3,500
3.5
3,531
13,500
20,535
3,900
2,600
3.5
6,504
V
OUT
Total Error
Homebrew
(ppm)
3,600
70
2.45
25,000
10,000
38,672
3,000
4,200
7
7,207
45,879