Datasheet AD8551, AD8552, AD8554 (Analog Devices) - 20
| Manufacturer | Analog Devices |
| Description | Sheet Zero-Drift, Single-Supply, Rail-to-Rail Input/Output Operational Amplifiers |
| Pages / Page | 24 / 20 — AD8551/AD8552/AD8554. Data Sheet. APPLICATIONS INFORMATION A 5 V … |
| Revision | F |
| File Format / Size | PDF / 512 Kb |
| Document Language | English |
AD8551/AD8552/AD8554. Data Sheet. APPLICATIONS INFORMATION A 5 V PRECISION STRAIN GAGE CIRCUIT. VOUT. AD8551/. AD8552/ AD8554
Model Line for this Datasheet
Text Version of Document
link to page 20 link to page 20 link to page 20 link to page 20 link to page 20 link to page 20
AD8551/AD8552/AD8554 Data Sheet APPLICATIONS INFORMATION A 5 V PRECISION STRAIN GAGE CIRCUIT R2
The extremely low offset voltage of the AD8552 makes it an
R1
ideal amplifier for any application requiring accuracy with high
V2 VOUT
gains, such as a weigh scale or strain gage. Figure 65 shows a
V1 AD8551/ R3
configuration for a single-supply, precision, strain gage
R4 AD8552/ AD8554
measurement system.
R4 R2 R2
066
IF = , THEN VOUT = × (V1 – V2)
A REF192 provides a 2.5 V precision reference voltage for A2.
R3 R1 R1
01101- The A2 amplifier boosts this voltage to provide a 4.0 V reference Figure 66. Using the AD8551/AD8552/AD8554 as a Difference Amplifier for the top of the strain gage resistor bridge. Q1 provides the In an ideal difference amplifier, the ratio of the resistors are set current drive for the 350 Ω bridge network. A1 is used to exactly equal to amplify the output of the bridge with the ful -scale output R R voltage equal to 2 4 = V A = (19) R R 2× (R + R ) 1 3 1 2 (17) R Which sets the output voltage of the system to B V where R OUT = AV (V1 − V2) (20) B is the resistance of the load cell. Due to finite component tolerance, the ratio between the four Using the values given in Figure 65, the output voltage linearly resistors is not exactly equal, and any mismatch results in a varies from 0 V with no strain to 4.0 V under full strain. reduction of common-mode rejection from the system. Referring to Figure 66, the exact common-mode rejection ratio can be
5V 2
expressed as
Q1 2.5V 3 REF192 1kΩ 2N2222 6 A2 OR
+ + 1 R 4 R 2R2 4 R R2 3 R =
EQUIVALENT AD8552-B 4
CMRR (21) 2R R − 2R R
12.0kΩ 20kΩ
1 4 2 3
4.0V R
In the three-op amp, instrumentation amplifier configuration
1 R2 17.4kΩ 100Ω
shown in Figure 67, the output difference amplifier is set to unity gain with all four resistors equal in value. If the tolerance
V 40mV A1 OUT
of the resistors used in the circuit is given as δ, the worst-case
0V TO 4.0V FULL-SCALE 350Ω AD8552-A LOAD
CMRR of the instrumentation amplifier is
CELL R3 R4 17.4kΩ 100Ω
CMRR 1 = MIN (22) δ 2
NOTES
065
1. USE 0.1% TOLERANCE RESISTORS.
01101-
AD8554-A
Figure 65. A 5 V Precision Strain Gage Amplifier
V2 R 3 V INSTRUMENTATION AMPLIFIER R R
The high common-mode rejection, high open-loop gain, and
RG VOUT
operation down to 3 V of supply voltage makes the AD8551/
R R AD8554-C R
AD8552/AD8554 an excel ent choice of op amp for discrete single-supply instrumentation amplifiers. The common-mode
V1 RTRIM AD8554-B
rejection ratio of the AD8551/AD8552/AD8554 is greater than 120 dB, but the CMRR of the system is also a function of the
2R
067
VOUT = 1 + (V1 – V2) RG
external resistor tolerances. The gain of the difference amplifier 01101- Figure 67. A Discrete Instrumentation Amplifier Configuration shown in Figure 66 is given as Consequently, using 1% tolerance resistors results in a worst-case R R R V = 4 V1 1+ 1 − system CMRR of 0.02, or 34 dB. Therefore, either high precision OUT V 2 2 (18) R + 3 R4 R2 1 R resistors or an additional trimming resistor, as shown in Figure 67, must be used to achieve high common-mode rejection. The value of this trimming resistor must be equal to the value of R multiplied by its tolerance. For example, using 10 kΩ resistors with 1% tolerance requires a series trimming resistor equal to 100 Ω. Rev. F | Page 20 of 24 Document Outline FEATURES APPLICATIONS GENERAL DESCRIPTION PIN CONFIGURATIONS TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ELECTRICAL CHARACTERISTICS ABSOLUTE MAXIMUM RATINGS THERMAL CHARACTERISTICS ESD CAUTION TYPICAL PERFORMANCE CHARACTERISTICS FUNCTIONAL DESCRIPTION AMPLIFIER ARCHITECTURE BASIC AUTO-ZERO AMPLIFIER THEORY Auto-Zero Phase Amplification Phase HIGH GAIN, CMRR, PSRR MAXIMIZING PERFORMANCE THROUGHPROPER LAYOUT 1/f NOISE CHARACTERISTICS INTERMODULATION DISTORTION BROADBAND AND EXTERNAL RESISTOR NOISE CONSIDERATIONS OUTPUT OVERDRIVE RECOVERY INPUT OVERVOLTAGE PROTECTION OUTPUT PHASE REVERSAL CAPACITIVE LOAD DRIVE POWER-UP BEHAVIOR APPLICATIONS INFORMATION A 5 V PRECISION STRAIN GAGE CIRCUIT 3 V INSTRUMENTATION AMPLIFIER A HIGH ACCURACY THERMOCOUPLE AMPLIFIER PRECISION CURRENT METER PRECISION VOLTAGE COMPARATOR OUTLINE DIMENSIONS ORDERING GUIDE
AD8551/AD8552/AD8554 Data Sheet APPLICATIONS INFORMATION A 5 V PRECISION STRAIN GAGE CIRCUIT R2
The extremely low offset voltage of the AD8552 makes it an
R1
ideal amplifier for any application requiring accuracy with high
V2 VOUT
gains, such as a weigh scale or strain gage. Figure 65 shows a
V1 AD8551/ R3
configuration for a single-supply, precision, strain gage
R4 AD8552/ AD8554
measurement system.
R4 R2 R2
066
IF = , THEN VOUT = × (V1 – V2)
A REF192 provides a 2.5 V precision reference voltage for A2.
R3 R1 R1
01101- The A2 amplifier boosts this voltage to provide a 4.0 V reference Figure 66. Using the AD8551/AD8552/AD8554 as a Difference Amplifier for the top of the strain gage resistor bridge. Q1 provides the In an ideal difference amplifier, the ratio of the resistors are set current drive for the 350 Ω bridge network. A1 is used to exactly equal to amplify the output of the bridge with the ful -scale output R R voltage equal to 2 4 = V A = (19) R R 2× (R + R ) 1 3 1 2 (17) R Which sets the output voltage of the system to B V where R OUT = AV (V1 − V2) (20) B is the resistance of the load cell. Due to finite component tolerance, the ratio between the four Using the values given in Figure 65, the output voltage linearly resistors is not exactly equal, and any mismatch results in a varies from 0 V with no strain to 4.0 V under full strain. reduction of common-mode rejection from the system. Referring to Figure 66, the exact common-mode rejection ratio can be
5V 2
expressed as
Q1 2.5V 3 REF192 1kΩ 2N2222 6 A2 OR
+ + 1 R 4 R 2R2 4 R R2 3 R =
EQUIVALENT AD8552-B 4
CMRR (21) 2R R − 2R R
12.0kΩ 20kΩ
1 4 2 3
4.0V R
In the three-op amp, instrumentation amplifier configuration
1 R2 17.4kΩ 100Ω
shown in Figure 67, the output difference amplifier is set to unity gain with all four resistors equal in value. If the tolerance
V 40mV A1 OUT
of the resistors used in the circuit is given as δ, the worst-case
0V TO 4.0V FULL-SCALE 350Ω AD8552-A LOAD
CMRR of the instrumentation amplifier is
CELL R3 R4 17.4kΩ 100Ω
CMRR 1 = MIN (22) δ 2
NOTES
065
1. USE 0.1% TOLERANCE RESISTORS.
01101-
AD8554-A
Figure 65. A 5 V Precision Strain Gage Amplifier
V2 R 3 V INSTRUMENTATION AMPLIFIER R R
The high common-mode rejection, high open-loop gain, and
RG VOUT
operation down to 3 V of supply voltage makes the AD8551/
R R AD8554-C R
AD8552/AD8554 an excel ent choice of op amp for discrete single-supply instrumentation amplifiers. The common-mode
V1 RTRIM AD8554-B
rejection ratio of the AD8551/AD8552/AD8554 is greater than 120 dB, but the CMRR of the system is also a function of the
2R
067
VOUT = 1 + (V1 – V2) RG
external resistor tolerances. The gain of the difference amplifier 01101- Figure 67. A Discrete Instrumentation Amplifier Configuration shown in Figure 66 is given as Consequently, using 1% tolerance resistors results in a worst-case R R R V = 4 V1 1+ 1 − system CMRR of 0.02, or 34 dB. Therefore, either high precision OUT V 2 2 (18) R + 3 R4 R2 1 R resistors or an additional trimming resistor, as shown in Figure 67, must be used to achieve high common-mode rejection. The value of this trimming resistor must be equal to the value of R multiplied by its tolerance. For example, using 10 kΩ resistors with 1% tolerance requires a series trimming resistor equal to 100 Ω. Rev. F | Page 20 of 24 Document Outline FEATURES APPLICATIONS GENERAL DESCRIPTION PIN CONFIGURATIONS TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ELECTRICAL CHARACTERISTICS ABSOLUTE MAXIMUM RATINGS THERMAL CHARACTERISTICS ESD CAUTION TYPICAL PERFORMANCE CHARACTERISTICS FUNCTIONAL DESCRIPTION AMPLIFIER ARCHITECTURE BASIC AUTO-ZERO AMPLIFIER THEORY Auto-Zero Phase Amplification Phase HIGH GAIN, CMRR, PSRR MAXIMIZING PERFORMANCE THROUGHPROPER LAYOUT 1/f NOISE CHARACTERISTICS INTERMODULATION DISTORTION BROADBAND AND EXTERNAL RESISTOR NOISE CONSIDERATIONS OUTPUT OVERDRIVE RECOVERY INPUT OVERVOLTAGE PROTECTION OUTPUT PHASE REVERSAL CAPACITIVE LOAD DRIVE POWER-UP BEHAVIOR APPLICATIONS INFORMATION A 5 V PRECISION STRAIN GAGE CIRCUIT 3 V INSTRUMENTATION AMPLIFIER A HIGH ACCURACY THERMOCOUPLE AMPLIFIER PRECISION CURRENT METER PRECISION VOLTAGE COMPARATOR OUTLINE DIMENSIONS ORDERING GUIDE
