Datasheet AD524 (Analog Devices) - 18
| Manufacturer | Analog Devices |
| Description | Precision Instrumentation Amplifier |
| Pages / Page | 25 / 18 — AD524. Data Sheet. GROUNDING. REFERENCE TERMINAL. ANALOG P.S. DIGITAL … |
| Revision | G |
| File Format / Size | PDF / 590 Kb |
| Document Language | English |
AD524. Data Sheet. GROUNDING. REFERENCE TERMINAL. ANALOG P.S. DIGITAL P.S. +15V C –15V. +5V. 0.1 0.1. 1µF 1µF. 1µF. DIG. COM. AD583. DIGITAL. SAMPLE
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AD524 Data Sheet GROUNDING
Typically, IC instrumentation amplifiers are rated for a full Many data acquisition components have two or more ground ±10 volt output swing into 2 kΩ. In some applications, however, pins that are not connected together within the device. These the need exists to drive more current into heavier loads. grounds must be tied together at one point, usual y at the system Figure 44 shows how a high current booster may be connected power-supply ground. Ideally, a single solid ground would be inside the loop of an instrumentation amplifier to provide the desirable. However, because current flows through the ground required current boost without significantly degrading overall wires and etch stripes of the circuit cards, and because these performance. Nonlinearities and offset and gain inaccuracies of paths have resistance and inductance, hundreds of millivolts can the buffer are minimized by the loop gain of the AD524 output be generated between the system ground point and the data amplifier. Offset drift of the buffer is similarly reduced. acquisition components. Separate ground returns should be
REFERENCE TERMINAL
provided to minimize the current flow in the path from the The reference terminal can be used to offset the output by up to sensitive points to the system ground point. In this way, supply ±10 V. This is useful when the load is floating or does not share currents and logic-gate return currents are not summed into the a ground with the rest of the system. It also provides a direct same return path as analog signals where they would cause means of injecting a precise offset. It must be remembered that measurement errors. the total output swing is ±10 V to be shared between signal and Because the output voltage is developed with respect to the reference offset. potential on the reference terminal, an instrumentation When the AD524 is of the 3-amplifier configuration it amplifier can solve many grounding problems. is necessary that nearly zero impedance be presented to the reference terminal.
ANALOG P.S. DIGITAL P.S. +15V C –15V C +5V
Any significant resistance from the reference terminal to ground increases the gain of the noninverting signal path, thereby upsetting the common-mode rejection of the AD524.
0.1 0.1 0.1 0.1 1µF 1µF 1µF µF µF µF µF
In the AD524, a reference source resistance unbalances the CMR
DIG 8
trim by the ratio of 20 kΩ/R
COM
REF. For example, if the reference
7 2 7 9 11 15 1 10
source impedance is 1 Ω, CMR is reduced to 86 dB (20 kΩ/1 Ω
AD524 AD583 9 DIGITAL SAMPLE AD574A DATA
= 86 dB). An operational amplifier can be used to provide that
1 AND HOLD OUTPUT 6
low impedance reference point, as shown in Figure 45. The
ANALOG
input offset voltage characteristics of that amplifier adds directly
OUTPUT SIGNAL GROUND* REFERENCE GROUND
to the output offset voltage performance of the instrumentation 043
*IF INDEPENDENT; OTHERWISE, RETURN AMPLIFIER REFERENCE
amplifier.
TO MECCA AT ANALOG P.S. COMMON.
00500- Figure 43. Basic Grounding Practice
+VS SENSE TERMINAL SENSE VIN+ 2 8 10 3
The sense terminal is the feedback point for the instrument
AD524 9
amplifier’s output amplifier. Normally, it is connected to the
12 6 REF LOAD
instrument amplifier output. If heavy load currents are to be
V 7 IN– 1
drawn through long leads, voltage drops due to current flowing
–VS
through lead resistance can cause errors. The sense terminal can 045
AD711 VOFFSET
be wired to the instrument amplifier at the load, thus putting 00500- Figure 45. Use of Reference Terminal to Provide Output Offset the IxR drops inside the loop and virtually eliminating this error source. An instrumentation amplifier can be turned into a voltage- to-current converter by taking advantage of the sense and
V+ (SENSE) OUTPUT
reference terminals, as shown in Figure 46.
CURRENT VIN+ 2 8 BOOSTER SENSE 3 10 +INPUT 2 + 9 X1 AD524 10 12 6 3 R1 R AD524 9 I 7 (REF) L L VIN– 1 VX 13
044
6 –INPUT 1 – V–
00500-
REF
Figure 44. AD524 Instrumentation Amplifier with Output Current Booster
A2 AD711 LOAD VX VIN 40,000
046
I = = = L
(
1 +
)
R1 R1 RG
00500- Figure 46. Voltage-to-Current Converter Rev. G | Page 18 of 25 Document Outline FEATURES FUNCTIONAL BLOCK DIAGRAM GENERAL DESCRIPTION PRODUCT HIGHLIGHTS TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS CONNECTION DIAGRAMS ESD CAUTION TYPICAL PERFORMANCE CHARACTERISTICS TEST CIRCUITS THEORY OF OPERATION INPUT PROTECTION INPUT OFFSET AND OUTPUT OFFSET GAIN INPUT BIAS CURRENTS COMMON-MODE REJECTION GROUNDING SENSE TERMINAL REFERENCE TERMINAL PROGRAMMABLE GAIN AUTO-ZERO CIRCUITS ERROR BUDGET ANALYSIS REFERENCES OUTLINE DIMENSIONS ORDERING GUIDE
AD524 Data Sheet GROUNDING
Typically, IC instrumentation amplifiers are rated for a full Many data acquisition components have two or more ground ±10 volt output swing into 2 kΩ. In some applications, however, pins that are not connected together within the device. These the need exists to drive more current into heavier loads. grounds must be tied together at one point, usual y at the system Figure 44 shows how a high current booster may be connected power-supply ground. Ideally, a single solid ground would be inside the loop of an instrumentation amplifier to provide the desirable. However, because current flows through the ground required current boost without significantly degrading overall wires and etch stripes of the circuit cards, and because these performance. Nonlinearities and offset and gain inaccuracies of paths have resistance and inductance, hundreds of millivolts can the buffer are minimized by the loop gain of the AD524 output be generated between the system ground point and the data amplifier. Offset drift of the buffer is similarly reduced. acquisition components. Separate ground returns should be
REFERENCE TERMINAL
provided to minimize the current flow in the path from the The reference terminal can be used to offset the output by up to sensitive points to the system ground point. In this way, supply ±10 V. This is useful when the load is floating or does not share currents and logic-gate return currents are not summed into the a ground with the rest of the system. It also provides a direct same return path as analog signals where they would cause means of injecting a precise offset. It must be remembered that measurement errors. the total output swing is ±10 V to be shared between signal and Because the output voltage is developed with respect to the reference offset. potential on the reference terminal, an instrumentation When the AD524 is of the 3-amplifier configuration it amplifier can solve many grounding problems. is necessary that nearly zero impedance be presented to the reference terminal.
ANALOG P.S. DIGITAL P.S. +15V C –15V C +5V
Any significant resistance from the reference terminal to ground increases the gain of the noninverting signal path, thereby upsetting the common-mode rejection of the AD524.
0.1 0.1 0.1 0.1 1µF 1µF 1µF µF µF µF µF
In the AD524, a reference source resistance unbalances the CMR
DIG 8
trim by the ratio of 20 kΩ/R
COM
REF. For example, if the reference
7 2 7 9 11 15 1 10
source impedance is 1 Ω, CMR is reduced to 86 dB (20 kΩ/1 Ω
AD524 AD583 9 DIGITAL SAMPLE AD574A DATA
= 86 dB). An operational amplifier can be used to provide that
1 AND HOLD OUTPUT 6
low impedance reference point, as shown in Figure 45. The
ANALOG
input offset voltage characteristics of that amplifier adds directly
OUTPUT SIGNAL GROUND* REFERENCE GROUND
to the output offset voltage performance of the instrumentation 043
*IF INDEPENDENT; OTHERWISE, RETURN AMPLIFIER REFERENCE
amplifier.
TO MECCA AT ANALOG P.S. COMMON.
00500- Figure 43. Basic Grounding Practice
+VS SENSE TERMINAL SENSE VIN+ 2 8 10 3
The sense terminal is the feedback point for the instrument
AD524 9
amplifier’s output amplifier. Normally, it is connected to the
12 6 REF LOAD
instrument amplifier output. If heavy load currents are to be
V 7 IN– 1
drawn through long leads, voltage drops due to current flowing
–VS
through lead resistance can cause errors. The sense terminal can 045
AD711 VOFFSET
be wired to the instrument amplifier at the load, thus putting 00500- Figure 45. Use of Reference Terminal to Provide Output Offset the IxR drops inside the loop and virtually eliminating this error source. An instrumentation amplifier can be turned into a voltage- to-current converter by taking advantage of the sense and
V+ (SENSE) OUTPUT
reference terminals, as shown in Figure 46.
CURRENT VIN+ 2 8 BOOSTER SENSE 3 10 +INPUT 2 + 9 X1 AD524 10 12 6 3 R1 R AD524 9 I 7 (REF) L L VIN– 1 VX 13
044
6 –INPUT 1 – V–
00500-
REF
Figure 44. AD524 Instrumentation Amplifier with Output Current Booster
A2 AD711 LOAD VX VIN 40,000
046
I = = = L
(
1 +
)
R1 R1 RG
00500- Figure 46. Voltage-to-Current Converter Rev. G | Page 18 of 25 Document Outline FEATURES FUNCTIONAL BLOCK DIAGRAM GENERAL DESCRIPTION PRODUCT HIGHLIGHTS TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS CONNECTION DIAGRAMS ESD CAUTION TYPICAL PERFORMANCE CHARACTERISTICS TEST CIRCUITS THEORY OF OPERATION INPUT PROTECTION INPUT OFFSET AND OUTPUT OFFSET GAIN INPUT BIAS CURRENTS COMMON-MODE REJECTION GROUNDING SENSE TERMINAL REFERENCE TERMINAL PROGRAMMABLE GAIN AUTO-ZERO CIRCUITS ERROR BUDGET ANALYSIS REFERENCES OUTLINE DIMENSIONS ORDERING GUIDE
