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High Common-Mode Voltage Programmable Gain Difference Amplifier AD628
FEATURES
High common-mode input voltage range 120 V at VS = 15 V Gain range 0.1 to 100 Operating temperature range: -40C to 85C Supply voltage range Dual supply: 2.25 V to 18 V Single supply: 4.5 V to 36 V Excellent ac and dc performance Offset temperature stability RTI: 10 V/C max Offset: 1.5 V mV max CMRR RTI: 75 dB min, dc to 500 Hz, G = +1
FUNCTIONAL BLOCK DIAGRAM
REXT2 +VS REXT1
RG
100k -IN
10k G = +0.1 -IN A1 +IN 10k +IN -IN A2 OUT
100k +IN 10k
AD628
APPLICATIONS
High voltage current shunt sensing Programmable logic controllers Analog input front end signal conditioning +5 V, +10 V, 5 V, 10 V and 4 to 20 mA Isolation Sensor signal conditioning Power supply monitoring Electrohydraulic control Motor control
CFILT
Figure 1.
130 120 110 100
CMRR (dB)
90 80 70
VS = 15V
GENERAL DESCRIPTION
The AD628 is a precision difference amplifier that combines excellent dc performance with high common-mode rejection over a wide range of frequencies. When used to scale high voltages, it allows simple conversion of standard control voltages or currents for use with single-supply ADCs. A wideband feedback loop minimizes distortion effects due to capacitor charging of - ADCs. A reference pin (VREF) provides a dc offset for converting bipolar to single-sided signals. The AD628 converts +5 V, +10 V, 5 V, 10 V, and 4 to 20 mA input signals to a single-ended output within the input range of single-supply ADCs. The AD628 has an input common-mode and differential mode operating range of 120 V. The high common-mode input impedance makes the device well suited for high voltage measurements across a shunt resistor. The buffer amplifier's inverting input is available for making a remote Kelvin connection.
VS = 2.5V 60 50 40
02992-C-002
30 10 100 1k FREQUENCY (Hz) 10k 100k
Figure 2. CMRR vs. Frequency of the AD628
A precision 10 k resistor connected to an external pin is provided for either a low-pass filter or to attenuate large differential input signals. A single capacitor implements a lowpass filter. The AD628 operates from single and dual supplies and is available in an 8-lead SOIC or MSOP package. It operates over the standard industrial temperature range of -40C to +85C.
Rev. C
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.326.8703 (c) 2004 Analog Devices, Inc. All rights reserved.
02992-C-001
-VS
VREF
AD628 TABLE OF CONTENTS
Specifications..................................................................................... 3 Absolute Maximum Ratings............................................................ 7 ESD Caution.................................................................................. 7 Pin Configuration and Function Descriptions............................. 8 Typical Performance Characteristics ............................................. 9 Test Circuits..................................................................................... 13 Theory of Operation ...................................................................... 14 Applications..................................................................................... 15 Gain Adjustment......................................................................... 15 Input Voltage Range ................................................................... 15 Voltage Level Conversion .......................................................... 16 Current Loop Receiver............................................................... 17 Monitoring Battery Voltages ..................................................... 17 Filter Capacitor Values............................................................... 18 Kelvin Connection ..................................................................... 18 Outline Dimensions ....................................................................... 19 Ordering Guide........................................................................... 19 6/03--Data Sheet Changed from Rev. A to Rev. B Changes to General Description ................................................... 1 Changes to Specifications............................................................... 2 Changes to Ordering Guide ........................................................... 4 Changes to TPCs 4, 5, and 6........................................................... 5 Changes to TPC 9............................................................................ 6 Updated Outline Dimensions...................................................... 14 1/03--Data Sheet Changed from Rev. 0 to Rev. A Change to Ordering Guide............................................................. 4 11/02--Rev. 0: Initial Version
REVISION HISTORY
4/04--Data Sheet Changed from Rev. B to Rev. C Updated Format.................................................................Universal Changes to Specifications............................................................... 3 Changes to Absolute Maximum Ratings ...................................... 7 Changes to Figure 3......................................................................... 7 Changes to Figure 26..................................................................... 13 Changes to Figure 27..................................................................... 13 Changes to Theory of Operation ................................................ 14 Changes to Figure 29..................................................................... 14 Changes to Table 5......................................................................... 15 Changes to Gain Adjustment Section......................................... 15 Added the Input Voltage Range Section..................................... 15 Added Figure 30 ............................................................................ 15 Added Figure 31 ............................................................................ 15 Changes to Voltage Level Conversion Section .......................... 16 Changes to Figure 32..................................................................... 16 Changes to Table 6......................................................................... 16 Changes to Figure 33 and Figure 34............................................ 17 Changes to Figure 35..................................................................... 18 Changes to Kelvin Connection Section...................................... 18
Rev. C | Page 2 of 20
AD628 SPECIFICATIONS
TA = 25C, VS = 15 V, RL = 2 k, REXT1 = 10 k, REXT2 = , VREF = 0 unless otherwise noted. Table 1.
Parameter DIFF AMP + OUTPUT AMP Gain Equation Gain Range Offset Voltage vs. Temperature CMRR Conditions G = +0.1(1+ REXT1/REXT2). See Figure 29. VOCM = 0 V. RTI of input pins2. Output amp G = +1. RTI of input pins. G = +0.1 to +100. 500 Hz. -40C to +85C. VS = 10 V to 18 V. Min AD628AR Typ Max Min AD628ARM Typ Max Unit V/V V/V mV V/C dB dB dB (V/V)/C dB V V kHz kHz s V/s nV/Hz V p-p V/V % ppm/C ppm ppm mV V/C k k dB dB dB (V/V)/C k %
0.11 -1.5 4 75 75 70 77 -120 -120 1 94
100 +1.5 8
0.11 -1.5 4 75 75 70
100 +1.5 8
Minimum CMRR Over Temperature vs. Temperature PSRR (RTI) Input Voltage Range Common Mode Differential Dynamic Response Small Signal BW -3 dB Full Power Bandwidth Settling Time Slew Rate Noise (RTI) Spectral Density DIFF-AMP Gain Error vs. Temperature Nonlinearity vs. Temperature Offset Voltage vs. Temperature Input Impedance Differential Common Mode CMRR
4 77 +120 +120 -120 -120
1 94
4
+120 +120 600 5
G = +0.1. G = +0.1, to 0.01%, 100 V step.
600 5 40 0.3
40 0.3 300 15 0.1 +0.01
1 kHz. 0.1 Hz to 10 Hz.
300 15 0.1 +0.01
-0.1
3 RTI of input pins. -1.5
+0.1 5 5 10 +1.5 8
-0.1
3 -1.5
+0.1 5 5 10 +1.5 8
220 55 RTI of input pins. G = +0.1 to +100. 500 Hz. -40C to +85C. 75 75 70 1 10 -0.1 4 +0.1 -0.1 75 75 70
220 55
Minimum CMRR Over Temperature vs. Temperature Output Resistance Error
1 10
4 +0.1
Rev. C | Page 3 of 20
AD628
Parameter OUTPUT AMPLIFIER Gain Equation Nonlinearity Offset Voltage vs. Temperature Output Voltage Swing Bias Current Offset Current CMRR Open-Loop Gain POWER SUPPLY Operating Range Quiescent Current TEMPERATURE RANGE Conditions G = (1 + REXT1/REXT2). G = +1, VOUT = 10 V. RTI of output amp. RL = 10 k. RL = 2 k. Min AD628AR Typ Max Min AD628ARM Typ Max Unit V/V ppm mV V/C V V nA nA dB dB V mA C
-0.15 -14.2 -13.8 1.5 0.2
0.5 +0.15 0.6 +14.1 +13.6 3 0.5
-0.15 -14.2 -13.8 1.5 0.2 130 130
0.5 +0.15 0.6 +14.1 +13.6 3 0.5
VCM = 13 V. VOUT = 13 V.
130 130 2.25 -40 18 1.6 +85
2.25 -40
18 1.6 +85
1 2
To use a lower gain, see the Gain Adjustment section. The addition of the difference amp's and output amp's offset voltage does not exceed this specification.
Rev. C | Page 4 of 20
AD628
TA = 25C, VS = +5 V, RL = 2 k, REXT1 = 10 k, REXT2 = , VREF = +2.5 unless otherwise noted. Table 2.
Parameter DIFF AMP + OUTPUT AMP Gain Equation Gain Range Offset Voltage vs. Temperature CMRR Minimum CMRR Over Temperature vs. Temperature PSRR (RTI) Input Voltage Range Common Mode3 Differential Dynamic Response Small Signal BW -3 dB Full Power Bandwidth Settling Time Slew Rate Noise (RTI) Spectral Density DIFF-AMP Gain Error Nonlinearity vs. Temperature Offset Voltage vs. Temperature Input Impedance Differential Common Mode CMRR Minimum CMRR Over Temperature vs. Temperature Output Resistance Error OUTPUT AMPLIFIER Gain Equation Nonlinearity Output Offset Voltage vs. Temperature Output Voltage Swing Bias Current Offset Current CMRR Open-Loop Gain Conditions G = +0.1(1+ REXT1/REXT2). See Figure 29. VOCM = 2.25 V. RTI of input pins2. Output Amp G = +1. RTI of input pins. G = 0.1 to 100. 500 Hz. -40C to +85C. VS = 4.5 V to 10 V. Min AD628AR Typ Max Min AD628ARM Typ Max Unit V/V V/V mV V/C dB dB dB (V/V)/C dB V V kHz kHz s V/s nV/Hz V p-p V/V % ppm ppm mV V/C k k dB dB dB (V/V)/C k % V/V ppm mV V/C V V nA nA dB dB
0.11 -3.0 6 75 75 70 77 -12 -15 1 94
100 +3.0 15
0.11 -3.0 6 75 75 70
100 +3.0 15
4 77 +17 +15 -12 -15
1 94
4
+17 +15 440 30 15 0.3 350 15 0.1 +0.01 3
G = +0.1. G = +0.1, to 0.01%, 30 V step.
440 30 15 0.3 350 15 0.1 +0.01 3
1 kHz. 0.1 Hz to 10 Hz.
-0.1
RTI of input pins.
-2.5
+0.1 3 10 +2.5 10
-0.1
-2.5
+0.1 3 10 +2.5 10
220 55 RTI of input pins. G = +0.1 to +100. 500 Hz. -40C to +85C. 75 75 70 1 10 -0.1 G = (1 + REXT1/REXT2). G = +1, VOUT = 1 V to 4 V. RTI of output amp. RL = 10 k. RL = 2 k. 4 +0.1 -0.1 75 75 70
220 55
1 10
4 +0.1
-0.15 0.9 1 1.5 0.2
0.5 0.15 0.6 4.1 4 3 0.5
-0.15 0.9 1 1.5 0.2 130 130
0.5 0.15 0.6 4.1 4 3 0.5
VCM = 1 V to 4 V. VOUT = 1 V to 4 V.
Rev. C | Page 5 of 20
130 130
AD628
Parameter POWER SUPPLY Operating Range Quiescent Current TEMPERATURE RANGE Conditions Min 2.25 -40 AD628AR Typ Max +36 1.6 +85 Min AD628ARM Typ Max +36 1.6 +85 Unit V mA C
2.25 -40
1 2 3
To use a lower gain, see the Gain Adjustment section. The addition of the difference amp's and output amp's offset voltage does not exceed this specification. Greater values of voltage are possible with greater or lesser values of VREF.
Rev. C | Page 6 of 20
AD628 ABSOLUTE MAXIMUM RATINGS
Table 3.
Parameter Supply Voltage Internal Power Dissipation Input Voltage (Common Mode) Differential Input Voltage Output Short-Circuit Duration Storage Temperature Operating Temperature Range Lead Temperature Range (10 sec Soldering) Rating 18 V See Figure 3 120 V1 120 V1 Indefinite -65C to +125C -40C to +85C 300C
1.6 1.4 TJ = 150C
POWER DISSIPATION (W)
1.2 8-LEAD MSOP PACKAGE 1.0 0.8 0.6 0.4 0.2 0 -60 MSOP J (JEDEC; 4-LAYER BOARD) = 132.54C/W SOIC J (JEDEC; 4-LAYER BOARD) = 154C/W -40 -20 0 20 40 60 80 100
02992-C-003
8-LEAD SOIC PACKAGE
Stresses greater than those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
1
AMBIENT TEMPERATURE (C)
Figure 3. Maximum Power Dissipation vs. Temperature
When using 12 V supplies or higher (see the Input Voltage Range section).
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
Rev. C | Page 7 of 20
AD628 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
Table 4. Pin Function Descriptions
+IN 1 -VS 2
8
-IN
CFILT 4
5
OUT
Figure 4. Pin Configuration
02992-C-004
7 +VS AD628 TOP VIEW 3 (Not to Scale) 6 R VREF G
Pin No. 1 2 3 4 5 6 7 8
Mnemonic +IN -VS VREF CFILT OUT RG +VS -IN
Function Noninverting Input Negative Supply Voltage Reference Voltage Input Filter Capacitor Connection Amplifier Output Output Amplifier Inverting Input Positive Supply Voltage Inverting Input
Rev. C | Page 8 of 20
AD628 TYPICAL PERFORMANCE CHARACTERISTICS
40 8440 UNITS 35 30 25 20 15 10 5
02992-C-005
140 G = +0.1 120 100
PSRR (dB)
% OF UNITS
80 -15V 60 +2.5V 40 20 +15V
-1.2
-0.8
-0.4
0
0.4
0.8
1.2
1.6
2.0
1
10
100
1k
10k
100k
1M
INPUT OFFSET VOLTAGE (mV)
FREQUENCY (Hz)
Figure 5. Typical Distribution of Input Offset Voltage, VS = 15 V, SOIC Package
25 8440 UNITS 20
VOLTAGE NOISE DENSITY (nV/ Hz)
Figure 8. PSRR vs. Frequency, Single and Dual Supplies
1000
% OF UNITS
15
10
5
02992-C-006
-78
-82
-86
-90
-94
-98
-102
-106
-110
1
10
100
1k
10k
100k
CMRR (dB)
FREQUENCY (Hz)
Figure 6. Typical Distribution of Common-Mode Rejection, SOIC Package
130 120 110 100
CMRR (dB) VOLTAGE NOISE DENSITY (nV/ Hz)
Figure 9. Voltage Noise Spectral Density, RTI, VS = 15 V
1000
90 80 70
VS = 15V
VS = 2.5V 60 50 40
02992-C-007
10
100
1k FREQUENCY (Hz)
10k
100k
1
10
100
1k
10k
100k
FREQUENCY (Hz)
Figure 7. CMRR vs. Frequency
Figure 10. Voltage Noise Spectral Density, RTI, VS = 2.5 V
Rev. C | Page 9 of 20
02992-C-010
30
100
02992-C-009
0 -74
100
02992-C-008
0 -1.6
0 0.1
AD628
40 1s
100 90
9638 UNITS 35 30
% OF DEVICES
NOISE (5V/DIV)
25 20 15 10 5
10 0
02992-C-011
0
5 TIME (Sec)
10
0
1
2
3
4
5
6
7
8
9
10
GAIN ERROR (ppm)
Figure 11. 0.1 Hz to 10 Hz Voltage Noise, RTI
60 50
COMMON-MODE VOLTAGE (V)
150
Figure 14. Typical Distribution of +1 Gain Error
UPPER CMV LIMIT
40 30
GAIN (dB)
G = +100
100 -40C 50 +85C 0 +25C VREF = 0V
20 10 0 -10 -20 -30
G = +10
G = +1
-50 +85C
-40C
G = +0.1
-100
LOWER CMV LIMIT
02992-C-012
1k
10k
100k
1M
10M
0
5
10 VS (V)
15
20
FREQUENCY (Hz)
Figure 12. Small Signal Frequency Response, VOUT = 200 mV p-p, G = +0.1, +1, +10, and +100
60 50 40 30
GAIN (dB)
Figure 15. Common-Mode Operating Range vs. Power Supply Voltage for Three Temperatures
VS = 15V RL = 1k
500V
G = +100
OUTPUT ERROR (V)
100 90
20 10 0 -10 -20 -30
G = +10
RL = 2k
G = +1
RL = 10k
10 0
G = +0.1
4.0V
02992-C-013 02992-C-016
-40 10
100
1k
10k
100k
1M
FREQUENCY (Hz)
OUTPUT VOLTAGE (V)
Figure 13. Large Signal Frequency Response, VOUT = 20 V p-p, G = +0.1, +1, +10, and +100
Figure 16. Normalized Gain Error vs. VOUT, VS = 15 V
Rev. C | Page 10 of 20
02992-C-015
-40 100
-150
02992-C-014
0
AD628
100V
100 90
VS = 2.5V RL = 1k
100 90
500mV
OUTPUT ERROR (V)
RL = 2k
RL = 10k
10 0 10 0
500mV
02992-C-017
50mV
4s
02992-C-020
OUTPUT VOLTAGE (V)
Figure 17. Normalized Gain Error vs. VOUT, VS = 2.5 V
4
Figure 20. Small Signal Pulse Response, RL = 2 k, CL = 0 pF, Top: Input, Bottom: Output
500mV
100
3
90
BIAS CURRENT (nA)
2
10
1
0
50mV
02992-C-018
4s
02992-C-021
0 -40
-20
0
20
40
60
80
100
TEMPERATURE (C)
Figure 18. Bias Current vs. Temperature Buffer
15 -40C 10 -25C +85C 5 +25C
100 90
Figure 21. Small Signal Pulse Response, RL = 2 k, CL = 1000 pF, Top: Input, Bottom: Output
OUTPUT VOLTAGE SWING (V)
10.0 V
0 -40C -5 +85C -10 +25C -25C 10.0 V
10 0
40 s
02992-C-022
0
5
10
15
20
25
OUTPUT CURRENT (mA)
Figure 19. Output Voltage Operating Range vs. Output Current
02992-C-019
-15
Figure 22. Large Signal Pulse Response, RL = 2 k, CL = 1000 pF, Top: Input, Bottom: Output
Rev. C | Page 11 of 20
AD628
100 90
100 90
5V
5V
10mV
10 0 10 0
10mV
100s
02992-C-023
100s
02992-C-024
Figure 23. Settling Time to 0.01%, 0 V to 10 V Step
Figure 24. Settling Time to 0.01% 0 V to -10 V Step
Rev. C | Page 12 of 20
AD628 TEST CIRCUITS
HP3589A SPECTRUM ANALYZER
HP3561A SPECTRUM ANALYZER +VS
7
+VS
CFILT
4
-IN 100k
10k
10k +IN
-
AD829
-IN G = +0.1 +IN -IN OUT + G = +100
FET PROBE
-IN
8
100k
10k
10k
+IN
5
OUT
+IN 100k
10k VREF CFILT RG
AD628
+IN
1
100k
-IN G = +0.1 +IN 10k
3 2 6
-IN
AD628
-VS
VREF -VS
RG 10k
02992-C-027
-
10k
02992-C-025
AD707
+
Figure 25. CMRR vs. Frequency
SCOPE
Figure 27. Noise Tests
+VS 1 VAC +15V -IN 100k -IN G = +0.1 +IN -IN 10k 10k G = +100 +IN OUT 20 + G = +100
AD829
-
+IN 100k
10k
AD628
VREF -VS
CFILT
RG
02992-C-026
Figure 26. PSRR vs. Frequency
Rev. C | Page 13 of 20
AD628 THEORY OF OPERATION
The AD628 is a high common-mode voltage difference amplifier, combined with a user configurable output amplifier (see Figure 28 and Figure 29). Differential mode voltages in excess of 120 V are accurately scaled by a precision 11:1 voltage divider at the input. A reference voltage input is available to the user at Pin 3 (VREF). The output common-mode voltage of the difference amplifier is the same as the voltage applied to the reference pin. If the uncommitted amplifier is configured for gain, connecting Pin 3 to one end of the external gain resistor establishes the output common-mode voltage at Pin 5 (OUT). The output of the difference amplifier is internally connected to a 10 k resistor trimmed to better than 0.1% absolute accuracy. The resistor is connected to the noninverting input of the output amplifier and is accessible to the user at Pin 4 (CFILT). A capacitor may be connected to implement a low-pass filter, a resistor may be connected to further reduce the output voltage, or a clamp circuit may be connected to limit the output swing. The uncommitted amplifier is a high open-loop gain, low offset, low drift op amp, with its noninverting input connected to the internal 10 k resistor. Both inputs are accessible to the user. Careful layout design has resulted in exceptional commonmode rejection at higher frequencies. The inputs are connected to Pin 1 (+IN) and Pin 8 (-IN), which are adjacent to the power Pin 2 (-VS) and Pin 7 (+VS). Because the power pins are at ac ground, input impedance balance and, therefore, commonmode rejection, are preserved at higher frequencies.
100k -IN G = +0.1 -IN A1 +IN 100k +IN 10k -IN 10k +IN A2 OUT
RG
100k -IN
10k G = +0.1 -IN A1 +IN 10k +IN -IN A2 OUT
100k +IN 10k
02992-C-028
VREF
CFILT
Figure 28. Simplified Schematic
CFILT +VS
AD628
10k
-VS
VREF
RG REXT3
REFERENCE VOLTAGE
REXT2
REXT1
Figure 29. Circuit Connections
Rev. C | Page 14 of 20
02992-C-029
AD628 APPLICATIONS
GAIN ADJUSTMENT
The AD628 system gain is provided by an architecture consisting of two amplifiers. The gain of the input stage is fixed at 0.1; the output buffer is user adjustable as GA2 = 1 + REXT1/REXT2. The system gain is then
INPUT VOLTAGE RANGE
The common-mode input voltage range is determined by VREF and the supply voltage. The relation is expressed by
VCMUPPER 11(VS+ - 1.2 V) - 10 VREF VCMLOWER 11(VS - + 1.2 V) - 10 VREF
(1)
(2)
R GTOTAL = 0.1x 1 + EXT1 R EXT2
At a 2 nA maximum, the input bias current of the buffer amplifier is very low and any offset voltage induced at the buffer amplifier by its bias current may be neglected (2 nA x 10 k = 20 V). However, to absolutely minimize bias current effects, REXT1 and REXT2 may be selected so that their parallel combination is 10 k. If practical resistor values force the parallel combination of REXT1 and REXT2 below 10 k, a series resistor (REXT3) may be added to make up for the difference. Table 5 lists several values of gain and corresponding resistor values. Table 5. Nearest Standard 1% Resistor Values for Various Gains (See Figure 29)
Total Gain (V/V) 0.1 0.2 0.25 0.5 1 2 5 10 A2 Gain (V/V) 1 2 2.5 5 10 20 50 100 REXT1 () 10 k 20 k 25.9 k 49.9 k 100 k 200 k 499 k 1M REXT2 () 20 k 18.7 k 12.4 k 11 k 10.5 k 10.2 k 10.2 k REXT3 () 0 0 0 0 0 0 0 0
where VS + is the positive supply, VS - is the negative supply and 1.2 V is the headroom needed for suitable performance. Equation 2 provides a general formula for calculating the common-mode input voltage range. However, the AD628 should be kept within the maximum limits listed in the Specifications table (Table 1) to maintain optimal performance. This is illustrated in Figure 30 where the maximum commonmode input voltage is limited to 120 V. Figure 31 shows the common-mode input voltage bounds for single-supply voltages.
200
INPUT COMMON-MODE VOLTAGE (V)
150 100 50 0 -50 -100 -150
02992-C-035 02992-C-034
MAXIMUM INPUT COMMON-MODE VOLTAGE WHEN VREF = GND
-200 0 2 4 6 8 10 12 14 16 SUPPLY VOLTAGE (V)
To set the system gain to less than 0.1, an attenuator may be created by placing a resistor, REXT4, from Pin 4 (CFILT) to the reference voltage. A divider would be formed by the 10 k resistor which is in series with the positive input of A2 and REXT4. A2 would be configured for unity gain. Using a divider and setting A2 to unity gain yields
Figure 30. Input Common-Mode Voltage vs. Supply Voltage for Dual Supplies
100
INPUT COMMON-MODE VOLTAGE (V)
80 60 40 20 0 -20 -40 -60 -80 0 2 4 6 8 10 12 14 16 SINGLE-SUPPLY VOLTAGE (V) MAXIMUM INPUT COMMON-MODE VOLTAGE WHEN VREF = MIDSUPPLY
REXT4 GW / DIVIDER = 0.1 x 10 k + REXT4
x1
Figure 31. Input Common-Mode Voltage vs. Supply Voltage for Single Supplies
Rev. C | Page 15 of 20
AD628
The differential input voltage range is constrained to the linear operation of the internal amplifiers A1 and A2. The voltage applied to the inputs of A1 and A2 should be between VS- + 1.2 V and VS+ - 1.2 V. Similarly, the outputs of A1 and A2 should be kept between VS- + 0.9 V and VS+ - 0.9 V. The design of such an application may be done in a few simple steps, which include the following:
* Determine the required gain. For example, if the input voltage must be transformed from 10 V to 0 V to +5 V, the gain is +5/+20 or +0.25. * Determine if the circuit common-mode voltage must be changed. An AD7715-5 ADC is illustrated for this example. When operating from a 5 V supply, the common-mode voltage of the AD7715 is half the supply or 2.5 V. If the AD628 reference pin and the lower terminal of the 10 k resistor are connected to a 2.5 V voltage source, the output common-mode voltage will be 2.5 V.
VOLTAGE LEVEL CONVERSION
Industrial signal conditioning and control applications typically require connections between remote sensors or amplifiers and centrally located control modules. Signal conditioners provide output voltages up to 10 V full scale; however, ADCs or microprocessors operating on single 3.3 V to 5 V logic supplies are becoming the norm. Thus, the controller voltages require further reduction in amplitude and reference. Furthermore, voltage potentials between locations are seldom compatible, and power line peaks and surges can generate destructive energy between utility grids. The AD628 is an ideal solution to both problems. It attenuates otherwise destructive signal voltage peaks and surges by a factor of 10 and shifts the differential input signal to the desired output voltage. Conversion from voltage-driven or current-loop systems is easily accommodated using the circuit in Figure 32. This shows a circuit for converting inputs of various polarities and amplitudes to the input of a single-supply ADC. Note that the common-mode output voltage can be adjusted by connecting Pin 3 (VREF) and the lower end of the 10 k resistor to the desired voltage. The output common-mode voltage will be the same as the reference voltage.
Table 6 shows resistor and reference values for commonly used single-supply converter voltages. REXT3 is included as an option. It is used to balance the source impedance into A2, which is described in more detail in the Gain Adjustment section.
Table 6. Nearest 1% Resistor Values for Voltages Level Conversion Applications
Input Voltage (V) 10 5 +10 +5 10 5 +10 +5 ADC Supply Voltage (V) 5 5 5 5 3 3 3 3 Desired Output Voltage (V) 2.5 2.5 2.5 2.5 1.25 1.25 1.25 1.25
AD7715-5
SERIAL CLOCK CLOCK NC SCLK MCLK IN MCLK OUT CS +5V RESET AVDD +IN OUT A2 -IN AIN(-) REF IN(+) REXT1 (SEE TABLE 5) AIN(+) REF IN(-) DGND DVDD DIN DOUT DRDY AGND +5V
VREF (V) 2.5 2.5 2.5 2.5 1.25 1.25 1.25 1.25
REXT1 (k) 15.0 39.7 39.7 89.8 2.49 15.0 15.0 39.7
REXT3 (k) 4.02 2.00 2.00 1.00 7.96 4.02 4.02 2.00
+VS
-IN (SEE TABLE 5)
100k
10k G = +0.1 -IN
10k
VIN +IN +IN 100k 10k VREF
A1
AD628
+2.5V
-VS
RG CFILT REXT3 10k
AD680
+5V
Figure 32. Level Shifter
Rev. C | Page 16 of 20
02992-C-030
(SEE TABLE 5)
AD628
CURRENT LOOP RECEIVER
Analog data transmitted on a 4 to 20 mA current loop may be detected with the receiver shown in Figure 33. The AD628 is an ideal choice for such a function, because the current loop must be driven with a compliance voltage sufficient to stabilize the loop, and the resultant common-mode voltage often exceeds commonly used supply voltages. Note that with large shunt values a resistance of equal value must be inserted in series with the inverting input to compensate for an error at the noninverting input.
+15V +VS
MONITORING BATTERY VOLTAGES
Figure 34 illustrates how the AD628 may be used to monitor a battery charger. Voltages approximately eight times the power supply voltage may be applied to the input with no damage. The resistor divider action is well suited for the measurement of many power supply applications, such as those found in battery chargers or similar equipment.
250 -IN
100k
10k
10k +IN A2 -IN OUT 0V TO 5V TO ADC
-IN 250 100k +IN 10k 4-20mA SOURCE VREF +IN
G = +0.1 A1
AD628
RG -VS -15V CFILT
REXT1 100k
2.5V REF
Figure 33. Level Shifter for 4 to 20 mA Current Loop
5V +VS nVBAT(V) -IN 100k 10k 10k +IN A2 CHARGING CIRCUIT +1.5V BATTERY +IN 10k 100k -IN +IN RG G = +0.1 A1 -IN REXT1 10k OUT
0V TO 5V TO ADC
-VS
VREF
CFILT
Figure 34. Battery Voltage Monitor
Rev. C | Page 17 of 20
02992-C-032
OTHER BATTERIES IN CHARGING CIRCUIT
AD628
02992-C-031
REXT2 11k
AD628
FILTER CAPACITOR VALUES
A capacitor may be connected to Pin 4 (CFILT) to implement a low-pass filter. The capacitor value is
C = 15.9/ft (F )
KELVIN CONNECTION
In certain applications, it may be desirable to connect the inverting input of an amplifier to a remote reference point. This eliminates errors resulting in circuit losses in interconnecting wiring. The AD628 is particularly suited for this type of connection. In Figure 35, a 10 k resistor is added in the feedback to match the source impedance of A2, which is described in more detail in the Gain Adjustment section.
5V +VS -IN 100k 10k 10k +IN A2 -IN OUT
where ft is the desired 3 dB filter frequency. Table 7 shows several frequencies and their closest standard capacitor values.
Table 7. Capacitor Values for Various Filter Frequencies
Frequency (Hz) 10 50 60 100 400 1k 5k 10 k Capacitor Value (F) 1.5 0.33 0.27 0.15 0.039 0.015 0.0033 0.0015
CIRCUIT LOSS
-IN +IN 100k +IN 10k
G = +0.1 A1
RG
10k LOAD
AD628
-VS VREF VS /2 CFILT
Figure 35. Kelvin Connection
Rev. C | Page 18 of 20
02992-C-033
AD628 OUTLINE DIMENSIONS
3.00 BSC
5.00 (0.1968) 4.80 (0.1890)
5
8
8
5 4
3.00 BSC
4
4.90 BSC
4.00 (0.1574) 3.80 (0.1497) 1
6.20 (0.2440) 5.80 (0.2284)
PIN 1 0.65 BSC 1.10 MAX 8 0 0.80 0.60 0.40
1.27 (0.0500) BSC 0.25 (0.0098) 0.10 (0.0040)
1.75 (0.0688) 1.35 (0.0532)
0.50 (0.0196) x 45 0.25 (0.0099)
0.15 0.00 0.38 0.22 COPLANARITY 0.10
0.23 0.08 SEATING PLANE
0.51 (0.0201) COPLANARITY SEATING 0.31 (0.0122) 0.10 PLANE
8 0.25 (0.0098) 0 1.27 (0.0500) 0.40 (0.0157) 0.17 (0.0067)
COMPLIANT TO JEDEC STANDARDS MO-187AA
COMPLIANT TO JEDEC STANDARDS MS-012AA CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS (IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
Figure 36. 8-Lead Mini Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters
Figure 37. 8-Lead Standard Small Outline Package [SOIC] Narrow Body (R-8) Dimensions shown in millimeters and (inches)
ORDERING GUIDE
Model AD628AR AD628AR-REEL AD628AR-REEL7 AD628ARM AD628ARM-REEL AD628ARM-REEL7 AD628-EVAL Temperature Range -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C Description 8-Lead SOIC 8-Lead SOIC 13" Reel 8-Lead SOIC 7" Reel 8-Lead MSOP 8-Lead MSOP 13" Reel 8-Lead MSOP 7" Reel Evaluation Board Package Option R-8 R-8 R-8 RM-8 RM-8 RM-8 Branding
JGA JGA JGA
Rev. C | Page 19 of 20
AD628 NOTES
(c) 2004 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. C02992-0-4/04(C)
Rev. C | Page 20 of 20

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