Datasheet

ManualsBrandsANALOG DEVICES ManualsLinear ICsLinear IC - In-amp InAmp LFCSP 16 VQ (4x4)

Zero Drift, Digitally Programmable

Instrumentation Amplifier

AD8231

Rev. B

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FEATURES

Digitally/pin-programmable gain

G = 1, 2, 4, 8, 16, 32, 64, or 128

Specified from −40°C to +125°C

50 nV/°C maximum input offset drift

10 ppm/°C maximum gain drift

Excellent dc performance

80 dB minimum CMR, G = 1

15 µV maximum input offset voltage

500 pA maximum bias current

0.7 µV p-p noise (0.1 Hz to 10 Hz)

Good ac performance

2.7 MHz bandwidth, G = 1

1.1 V/s slew rate

Rail-to-rail output

Shutdown/multiplex

Extra op amp

Single-supply range: 3 V to 5 V

Dual-supply range: ±1.5 V to ±2.5 V

Qualified for automotive applications

APPLICATIONS

Pressure and strain transducers

Thermocouples and RTDs

Programmable instrumentation

Industrial controls

Weigh scales

Automotive controls

FUNCTIONAL BLOCK DIAGRAM

06586-001

IN-AMP

LOGIC

–INA

+IN

–V

OUTA

REF

SDN

+INB

–INB

OUTB

AMP

AD8231

Figure 1.

Table 1. Instrumentation and Difference Amplifiers by

Summary of content (24 pages)

PAGE 1
Zero Drift, Digitally Programmable Instrumentation Amplifier AD8231 APPLICATIONS Pressure and strain transducers Thermocouples and RTDs Programmable instrumentation Industrial controls Weigh scales Automotive controls 3 CS 13 A0 14 10 4 9 OUTA REF OP AMP 06586-001 +INB 6 AD8231 5 –VS 8 NC 11 IN-AMP +VS OUTB +INA 2 LOGIC 7 –INA 12 1 –INB NC 15 16 A1 FUNCTIONAL BLOCK DIAGRAM SDN Digitally/pin-programmable gain G = 1, 2, 4, 8, 16, 32, 64, or 128 Specified from −40°C to +125°C
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AD8231 TABLE OF CONTENTS Features .............................................................................................. 1 Gain Selection............................................................................. 18 Applications....................................................................................... 1 Reference Terminal .................................................................... 18 Functional Block Diagram ..............................................................
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AD8231 SPECIFICATIONS VS = 5 V, VREF = 2.5 V, G = 1, RL = 10 kΩ, TA = 25°C, unless otherwise noted. Table 2. Parameter INSTRUMENTATION AMPLIFIER Offset Voltage Input Offset, VOSI Average Temperature Drift Output Offset, VOSO Average Temperature Drift Input Currents Input Bias Current Conditions Min Typ Max Unit 4 0.01 15 0.05 15 0.05 30 0.5 μV μV/°C μV μV/°C 250 500 5 100 0.5 pA nA pA nA 0.05 0.
PAGE 4
AD8231 Parameter Dynamic Performance Bandwidth G=1 G=2 Gain Bandwidth Product G = 4 to 128 Slew Rate Output Characteristics Output Voltage High Output Voltage Low Short-Circuit Current Digital Interface Input Voltage Low Input Voltage High Setup Time to CS High Hold Time after CS High OPERATIONAL AMPLIFIER Input Characteristics Offset Voltage, VOS Temperature Drift Input Bias Current Conditions RL = 100 kΩ to ground RL = 10 kΩ to ground RL = 100 kΩ to 5 V RL = 10 kΩ to 5 V TA = −40°C to +125°C TA = −40°C
PAGE 5
AD8231 VS = 3.0 V, VREF = 1.5 V, TA = 25°C, G = 1, RL = 10 kΩ, unless otherwise noted. Table 3. Parameter INSTRUMENTATION AMPLIFIER Offset Voltage Input Offset, VOSI Average Temperature Drift Output Offset, VOSO Average Temperature Drift Input Currents Input Bias Current Conditions Min Typ Max Unit 4 0.01 15 0.05 15 0.05 30 0.5 μV μV/°C μV μV/°C 250 500 5 100 0.5 pA nA pA nA 0.05 0.
PAGE 6
AD8231 Parameter Dynamic Performance Bandwidth G=1 G=2 Gain Bandwidth Product G = 4 to 128 Slew Rate Output Characteristics Output Voltage High Output Voltage Low Short-Circuit Current Digital Interface Input Voltage Low Input Voltage High Setup Time to CS High Hold Time after CS High OPERATIONAL AMPLIFIERS Input Characteristics Offset Voltage, VOS Temperature Drift Input Bias Current Conditions RL = 100 kΩ to ground RL = 10 kΩ to ground RL = 100 kΩ to 3 V RL = 10 kΩ to 3 V TA = −40°C to +125°C TA = −40°
PAGE 7
AD8231 ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE Table 4. Parameter Supply Voltage Output Short-Circuit Current Input Voltage (Common-Mode) Differential Input Voltage Storage Temperature Range Operational Temperature Range Package Glass Transition Temperature ESD (Human Body Model) ESD (Charged Device Model) ESD (Machine Model) Rating 6V Indefinite1 −VS − 0.3 V to +VS + 0.3 V −VS − 0.3 V to +VS + 0.3 V –65°C to +150°C –40°C to +125°C 130°C 1.5 kV 1.5 kV 0.
PAGE 8
AD8231 12 +VS 11 –VS 10 OUTA (IN-AMP OUT) 9 REF 14 A0 NOTES 1. NC = NO CONNECT. 2. THE EXPOSED PAD CAN BE CONNECTED TO THE NEGATIVE SUPPLY (–VS) OR LEFT FLOATING. 06586-002 (OP AMP OUT) OUTB 8 –INB 7 TOP VIEW (Not to Scale) SDN 5 NC 4 AD8231 +INB 6 (IN-AMP +IN) +INA 3 13 CS PIN 1 INDICATOR NC 1 (IN-AMP –IN) –INA 2 15 A1 16 A2 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS Figure 2. Pin Configuration Table 6.
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AD8231 TYPICAL PERFORMANCE CHARACTERISTICS INSTRUMENTATION AMPLIFIER PERFORMANCE CURVES 1000 1400 N: 5956 MEAN: 0.977167 SD: 11.8177 N: 5956 MEAN: –48.0779 1200 SD: 21.0433 800 1000 600 HITS HITS 800 400 600 400 200 –60 –40 –20 0 20 40 60 80 100 CMRR (µV/V) 0 –500 –400 –300 –200 –100 Figure 3. Instrumentation Amplifier CMR Distribution, G = 1 9 N: 5956 MEAN: 2.06788 700 SD: 1.07546 8 NUMBER OF AMPLIFIERS 600 400 300 200 100 300 400 500 N: 40 MEAN: –8.
PAGE 10
AD8231 6 VREF = MIDSUPPLY VCM = MIDSUPPLY 0V, 4.96V 1000 500 3V 0 5 4 5V SINGLE SUPPLY 0V, 2.96V 2 3V SINGLE SUPPLY 1 0 20 40 60 80 100 120 TEMPERATURE (°C) 0 06586-106 –20 Figure 9. Instrumentation Amplifier Bias Current vs. Temperature 0 2 3 4 5 6 Figure 12. Instrumentation Amplifier Input Common-Mode Range vs. Output Voltage, VREF = 0 V 6 INPUT COMMON-MODE VOLTAGE (V) 1.5 1.0 0.5 0 –0.5 –1.0 +VS = +2.5V –VS = –2.5V VREF = 0V –2.0 –2.5 –2.0 –1.5 –1.0 –0.5 0 0.5 1.
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AD8231 50 40 G = 64 10 G = 16 =1 =1 =8 =8 = 128 = 128 G=8 20 CMRR (µV/V) G=4 10 G=2 G=1 0 –10 5 0 –5 –15 –40 100 REPRESENTATIVE SAMPLES –20 –40 –20 0 20 40 1k 10k 100k 1M 10M FREQUENCY (Hz) 06586-009 –30 Figure 15. Instrumentation Amplifier Gain vs. Frequency G G G G G G G G 800 600 400 80 100 120 Figure 18. Instrumentation Amplifier CMRR vs.
PAGE 12
AD8231 G = +128, 0.4µV/DIV 1s/DIV 06586-012 G = +1, 1µV/DIV 10 1 0.1 0.01 1 10 100 1k 100k 10k FREQUENCY (Hz) Figure 21. Instrumentation Amplifier 0.1 Hz to 10 Hz Noise 100 06586-107 CURRENT NOISE (pA/ Hz) 100 Figure 24. Instrumentation Amplifier Current Noise Spectral Density G = +1 G = +8 G = +128 90 80 NOISE (nV/ Hz) 70 60 50 40 30 10 1 10 100 1k FREQUENCY (Hz) Figure 22. Instrumentation Amplifier Voltage Noise Spectral Density vs.
PAGE 13
AD8231 G = +8 G = +32 G = +128 2V/DIV 10µs/DIV 0.001%/DIV Figure 27. Instrumentation Amplifier Small Signal Pulse Response, G = 4, 16, and 128, RL = 2 kΩ, CL = 500 pF 100µs/DIV 06586-018 20mV/DIV 06586-015 17.6µs TO 0.01% 21.4µs TO 0.001% Figure 30. Instrumentation Amplifier Large Signal Pulse Response, G = 128, VS = 5 V 25 20 SETTLING TIME (µs) 2V/DIV 3.95µs TO 0.01% 4µs TO 0.001% 0.001% 15 0.01% 10 0 1 10 100 1k 06586-019 10µs/DIV 1k 06586-020 0.
PAGE 14
AD8231 +VS –0.4 –0.6 –0.8 –1.0 1.0 0.8 0.6 0.4 –0.4 –0.6 –0.8 –1.0 1.0 0.8 0.6 0.4 1 10 100 OUTPUT CURRENT (mA) –VS 0.1 1 10 100 OUTPUT CURRENT (mA) Figure 34. Instrumentation Amplifier Output Voltage Swing vs. Output Current, VS = 5 V Figure 33. Instrumentation Amplifier Output Voltage Swing vs. Output Current, VS = 3 V Rev. B | Page 14 of 24 06586-134 0.2 06586-133 0.2 –VS 0.1 –40°C +25°C +85°C +125°C –0.2 OUTPUT VOLTAGE SWING (V) REFERRED TO SUPPLY VOLTAGES –0.
PAGE 15
AD8231 –100 60 –110 40 –120 76° PHASE MARGIN 20 –130 0 –140 800pF 1nF 1.5nF 20mV/DIV 1k 10k 100k 1M –150 10M FREQUENCY (Hz) Figure 38. Operational Amplifier Small Signal Response for Various Capacitive Loads, VS = 3 V 60 –110 40 –120 72° PHASE MARGIN 20 –130 0 –140 RL = 10kΩ CL = 200pF –20 10 100 1k 10k 100k 1M –150 10M FREQUENCY (Hz) Figure 36. Operational Amplifier Open-Loop Gain and Phase vs. Frequency, VS = 3 V 800pF 1nF OUTPUT VOLTAGE (0.
PAGE 16
1000 +VS 900 –0.2 OUTPUT VOLTAGE SWING (V) REFERRED TO SUPPLY VOLTAGES 800 700 600 500 400 300 200 100 –0.4 –0.6 –0.8 –1.0 1.0 0.8 0.6 0.4 10 100 1k 10k 100k FREQUENCY (Hz) 06586-141 1 –VS 0.1 +VS 2.0 –0.2 OUTPUT VOLTAGE SWING (V) REFERRED TO SUPPLY VOLTAGES 2.2 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0 –0.2 –40 3V –25 100 –40°C +25°C +85°C +125°C –0.4 –0.6 –0.8 –1.0 1.0 0.8 0.6 0.4 0.2 5V –10 5 20 35 50 65 80 95 110 125 TEMPERATURE (°C) –VS 0.1 06586-108 0.2 10 Figure 44.
PAGE 17
AD8231 PERFORMANCE CURVES VALID FOR BOTH AMPLIFIERS 7 160 +125°C 6 CHANNEL SEPARATION (dB) +85°C +25°C 4 –40°C 3 2 1 120 G=1 100 80 60 40 20 3.5 3.9 4.3 4.7 5.1 5.5 VSUPPLY (V) 5.9 Figure 47. Supply Current vs. Supply Voltage 0 10 SOURCE CHANNEL: OP AMP AT G = 1 100 1k 10k FREQUENCY (Hz) Figure 48. Channel Separation vs. Frequency Rev. B | Page 17 of 24 100k 06586-149 3.1 06586-028 ISUPPLY (mA) G = 128 140 5 0 2.
PAGE 18
AD8231 THEORY OF OPERATION CS A0 A1 A2 SDN OUTB –INA 14kΩ A1 14kΩ –INB A4 +INB OUTA A3 14kΩ A2 14kΩ +VS –VS 06586-031 AD8231 +INA REF Figure 49. Simplified Schematic AMPLIFIER ARCHITECTURE Table 7. Truth Table for AD8231 Gain Settings The AD8231 is based on the classic 3-op amp topology. This topology has two stages: a preamplifier to provide amplification, followed by a difference amplifier to remove the common-mode voltage. Figure 49 shows a simplified schematic of the AD8231.
PAGE 19
AD8231 INCORRECT LAYOUT CORRECT +VS The AD8231 is a high precision device. To ensure optimum performance at the PCB level, care must be taken in the design of the board layout. The AD8231 pinout is arranged in a logical manner to aid in this task. +VS AD8231 AD8231 REF Power Supplies The AD8231 should be decoupled with a 0.1 μF bypass capacitor between the two supplies.
PAGE 20
AD8231 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 52.
PAGE 21
AD8231 APPLICATIONS INFORMATION DIFFERENTIAL OUTPUT Figure 53 shows how to create a differential output in-amp using the AD8231 uncommitted op amp. Because this configuration makes use of the reference terminal of the in-amp, errors from the op amp and resistor mismatch result in common-mode errors, rather than differential errors. Because common-mode errors are typically rejected by the next device in the signal chain, this circuit configuration adds almost no extra error.
PAGE 22
AD8231 When operating the AD8231 on dual supplies, a level-shift is typically needed from standard single-supply control logic. One easy way to accomplish the level-shift is through a single-pole, double-throw switch, such as the ADG633. Figure 55 shows an application schematic for ±2.5 V operation. VDIGITAL VDD +2.5V Note that in addition to setting the peaking of the filter, the ratio R3/R4 also sets the dc gain: G = 1 + R3/R4.
PAGE 23
AD8231 OUTLINE DIMENSIONS 4.00 BSC SQ 3.75 BSC SQ 0.75 0.60 0.50 0.80 MAX 0.65 TYP 12° MAX 1.00 0.85 0.80 0.65 BSC TOP VIEW SEATING PLANE 16 13 12 9 PIN 1 INDICATOR 1 2.25 2.10 SQ 1.95 8 5 4 0.25 MIN 1.95 BSC 0.05 MAX 0.02 NOM 0.35 0.30 0.25 (BOTTOM VIEW) 0.20 REF COPLANARITY 0.08 FOR PROPER CONNECTION OF THE EXPOSED PAD, REFER TO THE PIN CONFIGURATION AND FUNCTION DESCRIPTIONS SECTION OF THIS DATA SHEET. COMPLIANT TO JEDEC STANDARDS MO-220-VGGC 072808-A PIN 1 INDICATOR 0.60 MAX 0.