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G = 50, CMOS Sensor Amplifier with Current Excitation AD8290
FEATURES
Supply voltage range: 2.6 V to 5.5 V Low power 1.2 mA + 2x excitation current 0.5 A shutdown current Low input bias current: 100 pA High CMRR: 120 dB Space savings: 16-lead, 3.0 mm x 3.0 mm x 0.55 mm LFCSP Excitation current 300 A to 1300 A range Set with external resistor
GENERAL DESCRIPTION
The AD8290 contains both an adjustable current source to drive a sensor and a difference amplifier to amplify the signal voltage. The amplifier is set for a fixed gain of 50. The AD8290 is an excellent solution for both the drive and the sensing aspects required for pressure, temperature, and strain gage bridges. In addition, because the AD8290 operates with low power, works with a range of low supply voltages, and is available in a low profile package, it is suitable for drive/sense circuits in portable electronics as well. The AD8290 is available in a lead free 3.0 mm x 3.0 mm x 0.55 mm package and is operational over the industrial temperature range of -40C to +85C.
APPLICATIONS
Bridge and sensor drives Portable electronics
FUNCTIONAL BLOCK DIAGRAM
CFILTER RSET
13 10 15 11 6 5
ENBL
3 2
VCC GND
CBRIDGE
14
4
VREF NC
1
AD8290
NC
12
ANTIALIASING FILTER
ADC
NC
7
NC
8
NC
9
NC
16
06745-001
Figure 1.
Rev. B
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.
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AD8290 TABLE OF CONTENTS
Features .............................................................................................. 1 Applications....................................................................................... 1 General Description ......................................................................... 1 Functional Block Diagram .............................................................. 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 Absolute Maximum Ratings............................................................ 5 Thermal Resistance ...................................................................... 5 ESD Caution.................................................................................. 5 Pin Configuration and Function Descriptions............................. 6 Typical Performance Characteristics ............................................. 7 Theory of Operation ...................................................................... 14 Amplifier...................................................................................... 14 High Power Supply Rejection (PSR) and Common-Mode Rejection (CMR) ........................................................................ 14 1/f Noise Correction .................................................................. 14 Current Source............................................................................ 15 Applications Information .............................................................. 16 Typical Connections .................................................................. 16 Current Excitation...................................................................... 16 Enable/Disable Function ........................................................... 16 Output Filtering.......................................................................... 16 Clock Feedthrough..................................................................... 16 Maximizing Performance Through Proper Layout ............... 17 Power Supply Bypassing ............................................................ 17 Dual-Supply Operation ............................................................. 17 Pressure Sensor Bridge Application......................................... 18 Temperature Sensor Application.............................................. 19 ADC/Microcontroller................................................................ 19 Outline Dimensions ....................................................................... 20 Ordering Guide .......................................................................... 20
REVISION HISTORY
2/08--Rev. SpA to Rev. B Changes to Features Section............................................................ 1 Changes to Amplifier Section and Figure 43 .............................. 14 Changes to Current Source Section ............................................. 15 Changes to Current Excitation Section, Output Filtering Section, Clock Feedthrough Section, and Figure 45.................. 16 Changes to Figure 46...................................................................... 17 8/07--Revision SpA 7/07--Revision 0: Initial Version
Rev. B | Page 2 of 20
AD8290 SPECIFICATIONS
VCC = 2.6 V to 5.0 V, TA = 25C, CFILTER = 6.8 nF, output antialiasing capacitor = 68 nF, RSET = 3 k, common-mode input = 0.6 V, unless otherwise noted. Table 1.
Parameter COMMON-MODE REJECTION RATIO (CMRR) CMRR DC NOISE Amplifier and VREF VOLTAGE OFFSET Output Offset Output Offset TC PSR INPUT CURRENT Input Bias Current Input Offset Current DYNAMIC RESPONSE Small Signal Bandwidth -3 dB Test Conditions Input voltage (VINP - VINN) range of 0.2 V to VCC - 1.7 V Min Typ Max Unit
110 Input referred, f = 0.1 Hz to 10 Hz Reference is internal and set to 900 mV nominal -40C < TA < +85C 865 -300
120 0.75 900 50 120 100 200 0.25 935 +300
dB V p-p mV V/C dB pA pA kHz
-1000 -2000 With external filter capacitors, CFILTER = 6.8 nF and output antialiasing capacitor = 68 nF
+1000 +2000
GAIN Gain Gain Error Gain Nonlinearity Gain Drift INPUT Differential Input Impedance Input Voltage Range OUTPUT Output Voltage Range Output Series Resistance CURRENT EXCITATION Excitation Current Range Excitation Current Accuracy Excitation Current Drift External Resistor for Setting Excitation Current (RSET) Excitation Current Power Supply Rejection Excitation Current Pin Voltage Excitation Current Output Resistance Required Capacitor from Ground to Excitation Current Pin (CBRIDGE) ENABLE ENBL High Level ENBL Low Level Start-Up Time for ENBL
-1.0 -40C < TA < +85C -25
50 0.5 0.0075 15 50||1
+1.0 +25
V/V % % ppm/C M||pF V V k
0.2 VOUT = Gain x (VINP - VINN) + Output Offset 0.075 10 20% Excitation current = 0.9 V/RSET -40C < TA < +85C 300 -1.0 -250 692 -2.0 0 100 0.1
VCC - 1.7 VCC - 0.075
50
1300 +1.0 +250 3000 +2.0 VCC - 1.0
A % ppm/C A/V V M F
+0.2
VCC < 2.9 V VCC > 2.9 V
VCC - 0.5 2.4 GND 5.0
VCC VCC 0.8
V V V ms
Rev. B | Page 3 of 20
AD8290
Parameter POWER SUPPLY Operating Range Quiescent Current Shutdown Current TEMPERATURE RANGE For Operational Performance Test Conditions Min 2.6 1.2 + 2x excitation current 0.5 -40 Typ Max 5.5 1.8 + 2x excitation current 10 +85 Unit V mA A C
Rev. B | Page 4 of 20
AD8290 ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter Supply Voltage Input Voltage Differential Input Voltage 1 Output Short-Circuit Duration to GND Storage Temperature Range Operating Temperature Range Junction Temperature Range Lead Temperature (Soldering, 10 sec)
1
Rating 6V +VSUPPLY VSUPPLY Indefinite -65C to +150C -40C to +85C -65C to +150C 300C
Stresses above 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.
THERMAL RESISTANCE
JA is specified for the worst-case conditions, that is, a device soldered in a circuit board for surface-mount packages. Table 3.
Package Type 16-Lead LFCSP (0.55 mm) JA 42.5 JC 7.7 Unit C/W
Differential input voltage is limited to 5.0 V, the supply voltage, or whichever is less.
ESD CAUTION
Rev. B | Page 5 of 20
AD8290 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
13 IOUT
12 NC 11 RSET 10 GND 9 NC
NC 1 VCC 2 ENBL 3 VOUT 4
AD8290
TOP VIEW
(Not to Scale)
CF2 5
CF1 6
15 VINP
NC 7
14 VINN
16 NC
NC 8
NC = NO CONNECT
Figure 2. Pin Configuration
Table 4. Pin Function Descriptions
Pin No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17/Pad
1
Mnemonic NC VCC ENBL VOUT CF2 CF1 NC NC NC GND RSET NC IOUT VINN VINP NC NC
Description Tie to Ground 1 or Pin 16. Positive Power Supply Voltage. Logic 1 enables the part, and Logic 0 disables the part. Open End of Internal 10 k Resistor. Tie one end of external antialiasing filter capacitor (6.8 nF) to this pin, and tie the other end to ground.1 Tie one end of the CFILTER (68 nF) that is in parallel with the internal gain resistor to this pin. Tie the other end of the CFILTER (68 nF) that is in parallel with the internal gain resistor to this pin. Tie to Ground.1 Tie to Ground.1 Tie to Ground.1 Ground1 or Negative Power Supply Voltage. Tie one end of Resistor RSET to this pin to set the excitation current and tie the other end of Resistor RSET to Pin 10. Tie to Ground.1 Excitation Current Output. Tie one end of CBRIDGE (0.1 F) to this pin and tie the other end of CBRIDGE to ground.1 Negative Input Terminal. Positive Input Terminal. Tie to Ground1 or Pin 1. Pad should be floating and not tied to any potential.
During dual-supply operation, ground becomes the negative power supply voltage.
Rev. B | Page 6 of 20
06745-002
AD8290 TYPICAL PERFORMANCE CHARACTERISTICS
35 30
25
20
25
UNITS (%)
20 15 10
UNITS (%)
06745-003
15
10
5
5 0
OUTPUT VOLTAGE (mV)
0.2991
Figure 3. Output Offset Voltage at 2.6 V Supply
35 30
Figure 6. Excitation Output Current for 3 k RSET at 2.6 V Supply
25
20
25
UNITS (%)
15 10
UNITS (%)
20
15
10
5
5 0
OUTPUT VOLTAGE (mV)
0.2991
Figure 4. Output Offset Voltage at 3.6 V Supply
35 30
Figure 7. Excitation Output Current for 3 k RSET at 3.6 V Supply
25
20
25
UNITS (%)
15 10
UNITS (%)
20
15
10
5
5 0
OUTPUT VOLTAGE (mV)
0.2991
0.2997
0.3003
0.3009
EXCITATION CURRENT (mA)
Figure 5. Output Offset Voltage at 5.0 V Supply
Figure 8. Excitation Output Current for 3 k RSET at 5.0 V Supply
Rev. B | Page 7 of 20
06745-008
892
894
896
898
900
902
904
906
908
06745-005
0
0.2988
0.2994
0.3000
0.3006
0.3012
06745-007
892
894
896
898
900
902
904
906
908
06745-004
0
0.2988
0.2994
0.3000 0.3006 0.3012 0.2997 0.3003 0.3009 EXCITATION CURRENT (mA)
06745-006
892
894
896
898
900
902
904
906
908
0
0.2988
0.2994
0.3000 0.3006 0.3012 0.2997 0.3003 0.3009 EXCITATION CURRENT (mA)
AD8290
25
25
20
20
UNITS (%)
UNITS (%)
15
15
10
10
5
5
1.296 1.297 1.298 1.299 1.300 1.301 1.302 1.303 1.304 1.305 EXCITATION CURRENT (mA)
-0.60 -0.56 -0.52 -0.48 -0.44 -0.40 -0.36 -0.32 -0.28 GAIN ERROR (%)
Figure 9. Output Excitation Current for 692 RSET at 2.6 V Supply
25 25
Figure 12. Percent Gain Error at 2.6 V Supply
20
20
UNITS (%)
UNITS (%)
15
15
10
10
5
5
06745-010
1.296 1.297 1.298 1.299 1.300 1.301 1.302 1.303 1.304 1.305 EXCITATION CURRENT (mA)
-0.60 -0.56 -0.52 -0.48 -0.44 -0.40 -0.36 -0.32 -0.28 GAIN ERROR (%)
Figure 10. Output Excitation Current for 692 RSET at 3.6 V Supply
25
25
Figure 13. Percent Gain Error at 3.6 V Supply
20
20
UNITS (%)
10
UNITS (%)
15
15
10
5
5
06745-011
1.296 1.297 1.298 1.299 1.300 1.301 1.302 1.303 1.304 1.305 EXCITATION CURRENT (mA)
-0.60 -0.56 -0.52 -0.48 -0.44 -0.40 -0.36 -0.32 -0.28 GAIN ERROR (%)
Figure 11. Output Excitation Current for 692 RSET at 5.0 V Supply
Figure 14. Percent Gain Error at 5.0 V Supply
Rev. B | Page 8 of 20
06745-014
0
0
06745-013
0
0
06745-012
06745-009
0
0
AD8290
40 35
40 50
30 25 20 15 10
10 30
UNITS (%)
UNITS (%)
20
5
06745-031 06745-033 06745-032
0.0030
0.0035
0.0040
0.0050 0.0060 0.0070 0.0045 0.0055 0.0065 NONLINEARITY (%)
06745-026
0
0
-35
-15
5
25
45
65
85
105
125
DRIFT (V/C)
Figure 15. Percent Nonlinearity at 2.6 V Supply
35 30
Figure 18. Output Offset Voltage Drift from -40C to +85C at 2.6 V Supply
50
40
25
UNITS (%)
20 15 10
UNITS (%)
30
20
10
5 0
0
0.0030
0.0035
0.0040
0.0050 0.0060 0.0070 0.0045 0.0055 0.0065 NONLINEARITY (%)
06745-027
-35
-15
5
25
45
65
85
105
125
DRIFT (V/C)
Figure 16. Percent Nonlinearity at 3.6 V Supply
45 40 35 30
Figure 19. Output Offset Voltage Drift from -40C to +85C at 3.6 V Supply
50
40
UNITS (%)
25 20 15 10 5
06745-028
UNITS (%)
30
20
10
0
0
0.0030
0.0045
0.0060
0.0075 0.0105 NONLINEARITY (%)
0.0090
0.0120
0.0135
0.0150
-35
-15
5
25
45
65
85
105
125
DRIFT (V/C)
Figure 17. Percent Nonlinearity at 5.0 V Supply
Figure 20. Output Offset Voltage Drift from -40C to +85C at 5.0 V Supply
Rev. B | Page 9 of 20
AD8290
45 40 35 30 40 35 30 25
UNITS (%)
25 20 15 10 5
06745-035
UNITS (%)
20 15 10 5
06745-039 06745-041 06745-040
0
5
20
35
50
65
80
95
110
125
0
10
20
30
40
50
60
70
80
90
DRIFT (ppm/C)
DRIFT (ppm/C)
Figure 21. Excitation Current Drift from -40C to +85C at 2.6 V Supply, RSET = 3 k
45 40 35 30
Figure 24. Excitation Current Drift from -40C to +85C at 2.6 V Supply, RSET = 692
40 35 30 25
UNITS (%)
25 20 15 10 5
06745-036
UNITS (%)
20 15 10 5 0
0
5
20
35
50
65
80
95
110
125
10
20
30
40
50
60
70
80
90
DRIFT (ppm/C)
DRIFT (ppm/C)
Figure 22. Excitation Current Drift from -40C to +85C at 3.6 V Supply, RSET = 3 k
45 40 35 30
Figure 25. Excitation Current Drift from -40C to +85C at 3.6 V Supply, RSET = 692
40 35 30 25
UNITS (%)
25 20 15 10 5
06745-037
UNITS (%)
20 15 10 5 0
0
5
20
35
50
65
80
95
110
125
10
20
30
40
50
60
70
80
90
DRIFT (ppm/C)
DRIFT (ppm/C)
Figure 23. Excitation Current Drift from -40C to +85C at 5.0 V Supply, RSET = 3 k
Figure 26. Excitation Current Drift from -40C to +85C at 5.0 V Supply, RSET = 692
Rev. B | Page 10 of 20
AD8290
40 35 30 25 100
GAIN (V/V)
UNITS (%)
20 15 10 5
06745-045
10
-16.0 -15.5 -15.0 -14.5 -14.0 -13.5 -13.0 -12.5 -12.0 DRIFT (ppm/C)
1
10
100 FREQUENCY (Hz)
1k
10k
Figure 27. Gain Drift from -40C to +85C at 2.6 V Supply
40 35 30 25
Figure 30. Frequency Response for Supply Range of 2.6 V to 5.0 V (External CFILTER = 6.8 nF, Antialiasing Capacitor = 68 nF)
310 308 306
EXCITATION CURRENT (A)
304 302 300 298 296 294 292
UNITS (%)
20 15 10 5
06745-046
-16.0 -15.5 -15.0 -14.5 -14.0 -13.5 -13.0 -12.5 -12.0 DRIFT (ppm/C)
POWER SUPPLY (V)
Figure 28. Gain Drift from -40C to +85C at 3.6 V Supply
40 35 30 25
Figure 31. Low Excitation Current vs. Power Supply
1.310 1.308
EXCITATION CURRENT (mA)
1.306 1.304 1.302 1.300 1.298 1.296 1.294 1.292
UNITS (%)
20 15 10 5
06745-047
-16.0 -15.5 -15.0 -14.5 -14.0 -13.5 -13.0 -12.5 -12.0 DRIFT (ppm/C)
POWER SUPPLY (V)
Figure 29. Gain Drift from -40C to +85C at 5.0 V Supply
Figure 32. High Excitation Current vs. Power Supply
Rev. B | Page 11 of 20
06745-020
0
1.290 2.50 2.75 3.00 3.25 3.50 3.75 4.00 4.25 4.50 4.75 5.00 5.25 5.50
06745-019
0
290 2.50 2.75 3.00 3.25 3.50 3.75 4.00 4.25 4.50 4.75 5.00 5.25 5.50
06745-018
0
1
AD8290
310 50.0
305
49.9
EXCITATION CURRENT (A)
300
295
2.6V SUPPLY 3.6V SUPPLY
GAIN (V/V)
49.8
2.6V SUPPLY
49.7
5V SUPPLY 3.6V SUPPLY
290 5.0V SUPPLY 285 49.6
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
06745-021
5
15 25 35 45 55 65 75 85 95
PIN VOLTAGE (V)
TEMPERATURE (C)
Figure 33. Low Excitation Current vs. Excitation Current Pin Voltage
1.32 0.305 0.304 1.31
Figure 36. Gain vs. Temperature
EXCITATION CURRENT (mA)
EXCITATION CURRENT (mA)
0.303 0.302 5.0V SUPPLY 0.301 0.300 0.299 0.298 0.297 0.296 3.6V SUPPLY 2.6V SUPPLY
1.30
1.29
2.6V SUPPLY 3.6V SUPPLY
1.28 5.0V SUPPLY 1.27
06745-022
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5
15
25
35
45
55
65
75
85
95
PIN VOLTAGE (V)
TEMPERATURE (C)
Figure 34. High Excitation Current vs. Excitation Current Pin Voltage
0.905 0.904
Figure 37. Excitation Current vs. Temperature, RSET = 3 k
1.315
OUTPUT OFFSET (V)
0.902 0.901 0.900 0.899 0.898 5.0V SUPPLY 0.897 0.896
2.6V SUPPLY
EXCITATION CURRENT (mA)
0.903
1.310
1.305
5.0V SUPPLY
3.6V SUPPLY
1.300
2.6V SUPPLY 3.6V SUPPLY
1.295
1.290
06745-034
5
15
25
35
45
55
65
75
85
95
5
15
25
35
45
55
65
75
85
95
TEMPERATURE (C)
TEMPERATURE (C)
Figure 35. Output Offset Voltage vs. Temperature
Figure 38. Excitation Current vs. Temperature, RSET = 692
Rev. B | Page 12 of 20
06745-042
0.895 -45 -35 -25 -15 -5
1.285 -45 -35 -25 -15 -5
06745-038
1.26
0.295 -45 -35 -25 -15 -5
06745-052
280
49.5 -55 -45 -35 -25 -15 -5
AD8290
1.5 1.4 1000
QUIESCENT CURRENT (mA)
1.3 1.2 1.1 1.0 0.9 0.8 0.7
5.0V SUPPLY 3.6V SUPPLY 100
2.6V SUPPLY
NOISE (nV Hz)
10
5
15
25
35
45
55
65
75
85
95
06745-043
0.1
1
10
100
1000
TEMPERATURE (C)
FREQUENCY (Hz)
Figure 39. Quiescent Current vs. Temperature (Excludes 2x Excitation Current)
1.0 0.9
Figure 41. Input-Referred Noise vs. Frequency
INPUT-REFERRED NOISE (100nV/DIV)
0.8 0.7 0.6
ENBL PIN VOLTAGE (0V TO 5V)
OUTPUT OFFSET VOLTAGE
VOLTS (V)
0.5 0.4 0.3 0.2 0.1 0
06745-049
-5
0
5 TIME (ms)
10
15
20
TIME (10s/DIV)
Figure 40. 0.01 Hz to 10 Hz Input-Referred Noise
Figure 42. ENBL Pin Voltage for 5.0 V Supply vs. Output Offset Voltage Start-Up Time
Rev. B | Page 13 of 20
06745-050
-0.1 -10
06745-051
0.6 -45 -35 -25 -15 -5
1 0.01
AD8290 THEORY OF OPERATION
AMPLIFIER
The amplifier of the AD8290 is a precision current-mode correction instrumentation amplifier. It is internally set to a fixed gain of 50. The current-mode correction topology results in excellent accuracy. Figure 43 shows a simplified diagram illustrating the basic operation of the instrumentation amplifier within the AD8290 (without correction). The circuit consists of a voltage-to-current amplifier (M1 to M6), followed by a current-to-voltage amplifier (R2 and A1). Application of a differential input voltage forces a current through R1, resulting in a conversion of the input voltage to a signal current. Transistors M3 to M6 transfer twice the signal current to the inverting input of the op amp, A1. A1 and R2 form a current-to-voltage converter to produce a rail-torail output voltage, VOUT. Op Amp A1 is a high precision auto-zero amplifier. This amplifier preserves the performance of the autocorrecting, current-mode amplifier topology while offering the user a true voltage-in, voltage-out instrumentation amplifier. Offset errors are corrected internally. An internal 0.9 V reference voltage is applied to the noninverting input of A1 to set the output offset level. External Capacitor CFILTER is used to filter out correction noise.
VCC CFILTER I R1 I - IR1 IR1 = VINP M1 (VINP - VINN) R1 M2 VINN M3 M4 I M5 M6 I - IR1 I + IR1 VBIAS A1 VREF = 0.9V 2IR1 R3 VOUT = VREF R2
HIGH POWER SUPPLY REJECTION (PSR) AND COMMON-MODE REJECTION (CMR)
PSR and CMR indicate the amount that the offset voltage of an amplifier changes when its common-mode input voltage or power supply voltage changes. The autocorrection architecture of the AD8290 continuously corrects for offset errors, including those induced by changes in input or supply voltage, resulting in exceptional rejection performance. The continuous autocorrection provides great CMR and PSR performances over the entire operating temperature range (-40C to +85C).
1/f NOISE CORRECTION
Flicker noise, also known as 1/f noise, is noise inherent in the physics of semiconductor devices and decreases 10 dB per decade. The 1/f corner frequency of an amplifier is the frequency at which the flicker noise is equal to the broadband noise of the amplifier. At lower frequencies, flicker noise dominates causing large errors in low frequency or dc applications. Flicker noise appears as a slowly varying offset error that is reduced by the autocorrection topology of the AD8290, allowing the AD8290 to have lower noise near dc than standard low noise instrumentation amplifiers.
+
2R2 R1
VINP - VINN
EXTERNAL
Figure 43. Simplified Schematic of the Instrumentation Amplifier Within the AD8290
Rev. B | Page 14 of 20
06745-023
2I
2I
AD8290
CURRENT SOURCE
The AD8290 generates an excitation current that is programmable with an external resistor, RSET, as shown in Figure 44. A1 and M1 are configured to produce 0.9 V across RSET, which is based on an internal 0.9 V reference and creates a current equal to 0.9 V/RSET internal to the AD8290. This current is passed to a precision current mirror and a replica of the current is sourced from the IOUT pin. This current can be used for the excitation of a sensor bridge. CBRIDGE is used to filter noise from the current excitation circuit.
PRECISION CURRENT MIRROR
A1 VREF = 0.9V
M1
GND
RSET RSET
IOUT
CBRIDGE
06745-024
SENSOR BRIDGE
Figure 44. Current Excitation
Rev. B | Page 15 of 20
AD8290 APPLICATIONS INFORMATION
TYPICAL CONNECTIONS
Figure 45 shows the typical connections for single-supply operation when used with a sensor bridge. For bandwidths greater than 10 Hz, an additional single-pole RC filter of 235 Hz is required on the output, which is also recommended when driving an ADC requiring an antialiasing filter. Internal to the AD8290 is a series 10 k resistor at the output (R3 in Figure 43) and using an external 68 nF capacitor to ground produces an RC filter of 235 Hz on the output as well. These two filters produce an overall bandwidth of approximately 160 Hz for the output signal. In addition, when driving low impedances, the internal series 10 k resistor creates a voltage divider at the output. If it is necessary to access the output of the internal amplifier prior to the 10 k resistor, it is available at the CF2 pin. For applications with low bandwidths (<10 Hz), only the first filter capacitor (CFILTER) is required. In this case, the high frequency noise from the auto-zero amplifier (output amplifier) is not filtered before the following stage.
CURRENT EXCITATION
In Figure 45, RSET is used to set the excitation current sourced at the IOUT pin. The formula for the excitation current IOUT is IOUT = (900/RSET) mA where RSET is the resistor between Pin 10 (GND) and Pin 11 (RSET). The AD8290 is internally set by the factory to provide the current excitation described by the previous formula (within the tolerance range listed in Table 1). The range of RSET is 692 to 3 k, resulting in a corresponding IOUT of 1300 A to 300 A, respectively.
ENABLE/DISABLE FUNCTION
Pin 3 (ENBL) provides the enabling/disabling function of the AD8290 to conserve power when the device is not needed. A Logic 1 turns the part on and allows it to operate normally. A Logic 0 disables the output and excitation current and reduces the quiescent current to less than 10 A. The turn-on time upon switching Pin 3 high is dominated by the output filters. When the device is disabled, the output becomes high impedance, enabling the muxing application of multiple AD8290 instrumentation amplifiers.
CLOCK FEEDTHROUGH
The AD8290 uses two synchronized clocks to perform autocorrection. The input voltage-to-current amplifiers are corrected at 60 kHz. Trace amounts of these clock frequencies can be observed at the output. The amount of feedthrough is dependent upon the gain because the autocorrection noise has an input- and outputreferred term. The correction feedthrough is also dependent upon the values of the external capacitors, C2 and CFILTER.
OUTPUT FILTERING
Filter Capacitor CFILTER is required to limit the amount of switching noise present at the output. The recommended bandwidth of the filter created by CFILTER and an internal 100 k is 235 Hz. Select CFILTER based on CFILTER = 1/(235 x 2 x x 100 k) = 6.8 nF
CFILTER 6.8nF 5.0V RSET 692 TO 3k
11 6 5 3
RSET
CF1
CF2
ENBL VCC 2 C1 0.1F
13 IOUT
14
VINN
AD8290
GND 10 VOUT 4 VOUT C2 68nF
15 VINP
CBRIDGE
NC
1
NC
7
NC
8
NC
9
NC
12
NC
16
NC = NO CONNECT NOTES LAYOUT CONSIDERATIONS: 1. KEEP C1 CLOSE TO PIN 2 AND PIN 10. 2. KEEP RSET CLOSE TO PIN 11.
Figure 45. Typical Single-Supply Connections
Rev. B | Page 16 of 20
06745-025
AD8290
MAXIMIZING PERFORMANCE THROUGH PROPER LAYOUT
To achieve the maximum performance of the AD8290, care should be taken in the circuit board layout. The PCB surface must remain clean and free of moisture to avoid leakage currents between adjacent traces. Surface coating of the circuit board reduces surface moisture and provides a humidity barrier, reducing parasitic resistance on the board. RSET should be placed close to RSET (Pin 11) and GND (Pin 10). The paddle on the bottom of the package should not be connected to any potential and should be floating. For high impedance sources, the PCB traces from the AD8290 inputs should be kept to a minimum to reduce input bias current errors.
DUAL-SUPPLY OPERATION
The AD8290 can be configured to operate in dual-supply mode. An example of such a circuit is shown in Figure 46, where the AD8290 is powered by 1.8 V supplies. When operating with dual supplies, pins that are normally referenced to ground in the single-supply mode, now need to be referenced to the negative supply. These pins include the following: Pin 1, Pin 7, Pin 8, Pin 9, Pin 10, Pin 12, and Pin 16. External components, such as RSET, the sensing bridge, and the antialiasing filter capacitor at the output, should also be referenced to the negative supply. Additionally, two bypass capacitors should be added beyond what is necessary for single-supply operation: one between the negative supply and ground, and the other between the positive and negative supplies. When operating in dual-supply mode, the specifications change and become relative to the negative supply. The input voltage range minimum shifts from 0.2 V to 0.2 V above the negative supply (in this example: -1.6 V), the output voltage range shifts from a minimum of 0.075 V to 0.075 V above the negative supply (in this example: -1.725 V), and the excitation current pin voltage minimum shifts from 0 V to -1.8 V in this example. The maximum specifications of these three parameters are specified relative to VCC in Table 1 and do not change. For other specifications, both the minimum and maximum specifications change. The output offset shifts from a minimum of +865 mV and maximum of +935 mV to a minimum of -935 mV and a maximum of -865 mV in the example. In addition, the logic levels for the ENBL operation should be adjusted accordingly.
CFILTER 6.8nF 1.8V
POWER SUPPLY BYPASSING
The AD8290 uses internally generated clock signals to perform autocorrection. As a result, proper bypassing is necessary to achieve optimum performance. Inadequate or improper bypassing of the supply lines can lead to excessive noise and offset voltage. A 0.1 F surface-mount capacitor should be connected between Pin 2 (VCC) and Pin 10 (GND) when operating with a single supply and should be located as close as possible to those two pins.
RSET 692 TO 3k -1.8V
13
11
6
5
3
C3 0.1F
RSET
CF1
CF2
ENBL VCC 2 C1 0.1F -1.8V C5 0.1F
IOUT GND 10 VINN VINP VOUT 4
14
AD8290
15
VOUT C2 68nF
CBRIDGE
NC
1
NC
7
NC
8
NC
9
NC
12
NC
16
-1.8V NC = NO CONNECT NOTES LAYOUT CONSIDERATIONS: 1. KEEP C1 CLOSE TO PIN 2 AND PIN 10. 2. KEEP C3 CLOSE TO PIN 2. 3. KEEP C5 CLOSE TO PIN 10. 4. KEEP RSET CLOSE TO PIN 11.
-1.8V
Figure 46. Typical Dual-Supply Connections
Rev. B | Page 17 of 20
06745-029
AD8290
PRESSURE SENSOR BRIDGE APPLICATION
Given its excitation current range, the AD8290 provides a good match with pressure sensor circuits. Two such sensors are the Fujikura FGN-615PGSR and the Honeywell HPX050AS. Figure 47 shows the AD8290 paired with the Honeywell bridge and the appropriate connections. In this example, a resistor, RP, is added to the circuit to ensure that the maximum output voltage of the AD8290 is not exceeded. Depending on the sensors specifications, RP may not be necessary. The specifications for the bridge are show in Table 5 and the chosen conditions for the AD8290 are listed in Table 6. Given these specifications, calculations should be made to ensure that the AD8290 is operating within its required ranges. The combination of the excitation current and RP must be chosen to ensure that the conditions stay within the minimum and maximum specifications of the AD8290. For this example, because the specifications of the HPX050AS are for a bridge excitation voltage of 3.0 V, care must be taken to scale the resulting voltage calculations to the actual bridge voltage. The required calculations are shown in Table 7.
CFILTER 6.8nF 3.3V RSET 2.7k
11 6 5 3
RSET
CF1
CF2
ENBL VCC 2
13
IOUT VINN VINP
RP 2k
CBRIDGE 0.1F
2
8
HPX050AS
6
14
AD8290
GND 10
C1 0.1F
15 4 5
VOUT 4 NC
1
NC
7
NC
8
NC
9
NC
12
NC
16
C2 68nF
NC = NO CONNECT
Figure 47. HPX050AS Pressure Sensor Application
Table 5. HPX050AS Specifications
Bridge Impedance () Minimum Maximum 4000 6000 Rated Offset (mV) Minimum Maximum -30 +30 Rated Output Span (mV) Minimum Maximum 0 80 Bridge Excite Voltage (V) 3.0
Table 6. Typical AD8290 Conditions for Pressure Sensor Circuit
AD8290 VCC (V) 3.3 (2.6 to 5.5) Excitation Current (A) 333.3 (300 to 1300) Parallel Resistor RP () 2000
Table 7. Pressure Sensor Circuit Calculations Compared to AD8290 Minimum/Maximum Specifications
Specification Supply Current Current Setting Resistor (RSET) Minimum Equivalent Resistance to IOUT Pin Maximum Equivalent Resistance to IOUT Pin Minimum Current into Bridge Maximum Current into Bridge Minimum Bridge Midpoint Voltage (Excluding Offset/Span) Maximum Bridge Midpoint Voltage (Excluding Offset/Span) Minimum Voltage at Current Output Pin (IOUT) Maximum Voltage at Current Output Pin (IOUT) Input Voltage Minimum Input Voltage Maximum Output Voltage Minimum Output Voltage Maximum Calculation 1.867 2700 1333 1500 83.333 111.111 0.222 0.250 0.444 0.500 0.218 0.266 0.643 1.852
Rev. B | Page 18 of 20
Unit mA A A V V V V V V V V
Allowable Range of AD8290 692 to 3000
>0.0 V <2.3 V >0.2 V <1.6 V >0.075 V <3.225 V
06745-030
AD8290
TEMPERATURE SENSOR APPLICATION
The AD8290 can be used with a temperature sensor. Figure 48 shows the AD8290 in conjunction with an RTD, in this example, a 2-wire PT100. The specifications for the sensor are shown in Table 8 and the chosen conditions for the AD8290 are listed in Table 9. Once again, care must be taken when picking the excitation current and RG such that the minimum and maximum specifications of the AD8290 are not exceeded. Sample calculations are shown in Table 10.
ADC/MICROCONTROLLER
In both of the previous applications, an ADC or a microcontroller can be used to follow the AD8290 to convert the output analog signal to digital. For example, if there are multiple sensors in the system, the six channel ADuC814ARU microcontoller is an excellent candidate to interface with multiple AD8290s.
CFILTER 6.8nF 3.3V RSET 3k
11 6 5 3
RSET
CF1
CF2
ENBL VCC 2
13 IOUT
CBRIDGE 0.1F RTD
15
VINP
AD8290
GND 10
C1 0.1F
14 VINN
RG 698
VOUT 4 NC
1
NC
7
NC
8
NC
9
NC
12
NC
16
C2 68nF
NC = NO CONNECT
Figure 48. PT100 Temperature Sensor Application Connections
Table 8. PT100 Specifications
RTD Minimum @ 0C 100 RTD Maximum @ 100C 138.5
Table 9. Typical AD8290 Conditions for Temperature Sensor Circuit
AD8290 VCC (V) 3.30 (2.6 to 5.5) Excitation Current (A) 300 (300 to 1300) Resistor from RTD to GND, RG () 698
Table 10. Temperature Sensor Circuit Calculations Compared to AD8290 Minimum/Maximum Specifications
Specification Supply Current Current Setting Resistor (RSET) Minimum Equivalent Resistance to IOUT Pin Maximum Equivalent Resistance to IOUT Pin Minimum Voltage @ Current Output Pin (IOUT) Maximum Voltage @ Current Output Pin (IOUT) Input Voltage Minimum Input Voltage Maximum Output Voltage Minimum Output Voltage Maximum Calculation 1.8 3000 798 836.5 0.239 0.251 0.209 0.251 2.365 3.013 Unit mA V V V V V V Allowable Range of AD8290 692 to 3000
>0.0 V <2.3 V >0.2 V <1.6 V >0.075 V <3.225 V
Rev. B | Page 19 of 20
06745-044
AD8290 OUTLINE DIMENSIONS
INDEX AREA 3.00 BSC SQ
13 12 16 EXPOSED PAD 9 4
PIN 1 INDICATOR
1
1.80 1.70 SQ 1.55
5
0.50 BSC TOP VIEW 0.60 0.55 0.51 SEATING PLANE 0.30 0.25 0.18 0.05 MAX 0.02 NOM 0.08 REF
8
BOTTOM VIEW
0.40 MAX 0.30 NOM
COMPLIANT TO JEDEC STANDARDS MO-248-UEED.
Figure 49. 16-Lead Lead Frame Chip Scale Package [LFCSP_UQ] 3 mm x 3 mm Body, Ultra Thin Quad (CP-16-12) Dimensions shown in millimeters
ORDERING GUIDE
Model AD8290ACPZ-R2 1 AD8290ACPZ-R71 AD8290ACPZ-RL1
1
Temperature Range -40C to +85C -40C to +85C -40C to +85C
Package Description 16-Lead LFCSP_UQ 16-Lead LFCSP_UQ 16-Lead LFCSP_UQ
Package Option CP-16-12 CP-16-12 CP-16-12
053106-B
Branding Y0J Y0J Y0J
Z = RoHS Compliant Part.
(c)2007-2008 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D06745-0-2/08(B)
Rev. B | Page 20 of 20

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