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Low Cost, Zero-Drift In-Amp with Filter and Fixed Gain AD8293G80/AD8293G160
FEATURES
Small package: 8-lead SOT-23 Reduced component count Incorporates gain resistors and filter resistors Low offset voltage: 20 V maximum Low offset drift: 0.3 V/C maximum Low gain drift: 25 ppm/C maximum High CMR: 140 dB typical Low noise: 0.7 V p-p from 0.01 Hz to 10 Hz Single-supply operation: 1.8 V to 5.5 V Rail-to-rail output Available in 2 fixed-gain models
FUNCTIONAL BLOCK DIAGRAM
7 5 6
+VS +IN R1 4k
1
FILT R2
OUT
8
IN-AMP
R3 5k ADC OUT
4
-IN
OUTPUT TO ADC WITH ANTIALIASING FILTER
07451-001
GND REF
2 3
AD8293Gxx
Figure 1.
+5V
APPLICATIONS
Current sensing Strain gauges Laser diode control loops Portable medical instruments Thermocouple amplifiers
0.1F
7 5
C2
6
+VS LOAD
8
FILT R2
OUT
+IN R1 4k IN-AMP
I
RSHUNT
1
R3 5k ADC OUT
4
ADC C3 +3.3V REF
-IN GND REF
2 3
1.8V DC-DC
Figure 2. Measuring Current Using the AD8293G80/AD8293G160
Table 1. AD8293Gxx Models and Gains
Model AD8293G80 AD8293G160 Gain 80 160
GENERAL DESCRIPTION
The AD8293G80/AD8293G160 are small, low cost, precision instrumentation amplifiers that have low noise and rail-to-rail outputs. They are available in two fixed-gain models: 80 and 160. They incorporate the gain setting resistors and filter resistors, reducing the number of ancillary components. For example, only two external capacitors are needed to implement a 2-pole filter. The AD8293G80/AD8293G160 also feature low offset voltage, offset drift, and gain drift coupled with high commonmode rejection. They are capable of operating on a supply of 1.8 V to 5.5 V. With a low offset voltage of 20 V (AD8293G160B), an offset voltage drift of 0.3 V/C, and a voltage noise of only 0.7 V p-p (0.01 Hz to 10 Hz), the AD8293G80/AD8293G160 are ideal for applications where error sources cannot be tolerated. Precision instrumentation, position and pressure sensors, medical instrumentation, and strain gauge amplifiers benefit from the low noise, low input bias current, and high commonmode rejection. The small footprint and low cost are ideal for high volume applications. The small package and low power consumption allow the maximum channel density and the minimum board size required for portable systems. Designed for ease of use, these instrumentation amplifiers, unlike more traditional ones, have a buffered reference, eliminating the need for an additional op amp to set the reference voltage to midsupply. The AD8293G80/AD8293G160 are specified over the industrial temperature range from -40C to +85C. The AD8293G80/ AD8293G160 are available in a halogen-free, Pb-free, 8-lead SOT-23.
Rev. 0
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: 781.461.3113 (c)2008 Analog Devices, Inc. All rights reserved.
07451-002
AD8293Gxx
0.1F
10F
AD8293G80/AD8293G160 TABLE OF CONTENTS
Features .............................................................................................. 1 Applications ....................................................................................... 1 Functional Block Diagram .............................................................. 1 General Description ......................................................................... 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 Electrical Characteristics ............................................................. 3 Absolute Maximum Ratings............................................................ 5 Thermal Resistance ...................................................................... 5 ESD Caution .................................................................................. 5 Pin Configuration and Function Descriptions ............................. 6 Typical Performance Characteristics ............................................. 7 Theory of Operation ...................................................................... 10 High PSR and CMR ................................................................... 10 1/f Noise Correction .................................................................. 10 Applications Information .............................................................. 11 Overview ..................................................................................... 11 Reference Connection ............................................................... 11 Output Filtering .......................................................................... 11 Clock Feedthrough..................................................................... 12 Power Supply Bypassing ............................................................ 12 Input Overvoltage Protection ................................................... 12 Outline Dimensions ....................................................................... 13 Ordering Guide .......................................................................... 13
REVISION HISTORY
8/08--Revision 0: Initial Version
Rev. 0 | Page 2 of 16
AD8293G80/AD8293G160 SPECIFICATIONS
ELECTRICAL CHARACTERISTICS
VCC = 5.0 V, VCM = -0 V, VREF = 3.3 V, VIN = VINP - VINN, TA = 25C, tested at ADC OUT, unless otherwise noted. Temperature specifications guaranteed by characterization. Table 2. A Grade
Parameter COMMON-MODE REJECTION NOISE PERFORMANCE Voltage Noise Voltage Noise Density INPUT CHARACTERISTICS Input Offset Voltage vs. Temperature Input Bias Current Input Offset Current Input Operating Impedance Differential Common Mode Input Voltage Range DYNAMIC RESPONSE Small Signal Bandwidth 1 Slew Rate Settling Time 2 0.1% 0.01% Internal Clock Frequency GAIN Gain Error Gain Drift Nonlinearity OUTPUT CHARACTERISTICS Output Voltage High Output Voltage Low Short-Circuit Current REFERENCE CHARACTERISTICS VREF Range REF Pin Current POWER SUPPLY Operating Range Power Supply Rejection Supply Current TEMPERATURE RANGE Specified Range
1 2
Symbol CMR
Conditions VCM = 0 V to 3.3 V, -40C TA +85C f = 0.01 Hz to 10 Hz f = 1 kHz
Min 94
AD8293G80A Typ Max 140
Min 94
AD8293G160A Typ Max 140
Unit dB
en p-p en VOS VOS/T IB IOS
0.7 35 9 0.02 0.4 50 0.3 2 4
0.7 35 9 0.02 0.4 50 0.3 2 4
V p-p nV/Hz V V/C nA nA M||pF G||pF V Hz
-40C TA +85C -40C TA +85C
50||1 10||10 0 BW SR ts Filter limited VCC - 1.7 500 Filter limited 1.9 2.4 60 80 0.3 5 0.003 VCC - 0.075 0.075 35 0.8 IREF 1.8 94 0.01 VCC - 0.8 1 5.5 120 1.0 1.3 1.5 +85 -40 0.8 0
50||1 10||10 VCC - 1.7 500 Filter limited 1.9 2.4 60 160 0.3 5 0.003 VCC - 0.075 0.075 35 VCC - 0.8 1 5.5 120 1.0 1.3 1.5 +85
500 Hz filter, VO = 2 V step
ms ms kHz 1 25 0.03 % ppm/C % FS V V mA V nA V dB mA mA C
VO = 0.075 V to 4.925 V -40C TA +85C VO = 0.075 V to 4.925 V VOH VOL ISC
1 25 0.03
0.01 1.8 94
PSR ISY
VCC = 1.8 V to 5.5 V, VCM = 0 V IO = 0 mA, VIN = 0 V -40C TA +85C
-40
Higher bandwidths result in higher noise. Settling time is determined by filter setting.
Rev. 0 | Page 3 of 16
AD8293G80/AD8293G160
VCC = 2.7 V to 5.0 V, VCM = -0 V, VREF = VCC/2, VIN = VINP - VINN, TA = 25C, tested at OUT with 10 k load and ADC OUT, unless otherwise noted. Temperature specifications guaranteed by characterization. Table 3. B Grade (Tested and Guaranteed over a Wider Supply Range to More Stringent Specifications Than the A Grade)
Parameter COMMON-MODE REJECTION Symbol CMR Conditions VCC = 5 V, VCM = 0 V to 3.3 V; -40C TA +85C VCC = 2.7 V, VCM = 0 V to 1 V; -40C TA +85C f = 0.01 Hz to 10 Hz f = 1 kHz Min 110 106 AD8293G80B Typ Max 140 140 Min 110 106 AD8293G160B Typ Max 140 140 Unit dB dB
NOISE PERFORMANCE Voltage Noise Voltage Noise Density INPUT CHARACTERISTICS Input Offset Voltage vs. Temperature vs. Temperature Input Bias Current Input Offset Current Input Operating Impedance Differential Common Mode Input Voltage Range DYNAMIC RESPONSE Small Signal Bandwidth 1 Slew Rate Settling Time 2 0.1% 0.01% Internal Clock Frequency GAIN Gain Error Gain Drift Nonlinearity OUTPUT CHARACTERISTICS Output Voltage High Output Voltage Low Short-Circuit Current REFERENCE CHARACTERISTICS VREF Range REF Pin Current POWER SUPPLY Operating Range Power Supply Rejection Supply Current TEMPERATURE RANGE Specified Range
1 2
en p-p en VOS VOS/T VOS/T IB IOS
0.7 35 5 0.02 0.01 0.4 30 0.3 0.5 2 4
0.7 35 3 0.02 0.01 0.4 20 0.3 0.5 2 4
V p-p nV/Hz V V/C V/C nA nA M||pF G||pF V Hz
-40C TA +85C, VCC = 5 V -40C TA +85C, VCC = 2.7 V -40C TA +85C
50||1 10||10 0 BW SR ts 500 Hz filter, VO = 2 V step; measured at ADC OUT Filter limited; measured at ADC OUT 500 Filter limited 1.9 2.4 60 80 0.3 5 0.003 VCC - 0.075 0.075 VCC = 5 V VCC = 2.7 V 0.8 IREF 1.8 100 0.01 35 25 VCC - 0.8 1 5.5 120 1.0 1.3 1.5 +85 -40 0.8 VCC - 1.7 0
50||1 10||10 VCC - 1.7 500 Filter limited 1.9 2.4 60 160 0.3 5 0.003 VCC - 0.075 0.075 35 25 VCC - 0.8 1 5.5 120 1.0 1.3 1.5 +85
ms ms kHz 0.5 25 0.009 % ppm/C % FS V V mA mA V nA V dB mA mA C
VO = 0.075 V to 4.925 V -40C TA +85C VO = 0.075 V to 4.925 V VOH VOL ISC
0.5 25 0.009
0.01 1.8 100
PSR ISY
VCC = 1.8 V to 5.5 V, VCM = 0 V IO = 0 mA, VIN = 0 V -40C TA +85C
-40
Higher bandwidths result in higher noise. Settling time is determined by filter setting.
Rev. 0 | Page 4 of 16
AD8293G80/AD8293G160 ABSOLUTE MAXIMUM RATINGS
Table 4.
Parameter Supply Voltage Input Voltage Differential Input Voltage1 Output Short-Circuit Duration to GND Storage Temperature Range (RJ Package) Operating Temperature Range Junction Temperature Range (RJ Package) 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 5.
Package Type 8-Lead SOT-23 (RJ)
1
Differential input voltage is limited to 5.0 V, the supply voltage, or whichever is less.
JA1 211.5
JC 91.99
Unit C/W
JA is specified for the nominal conditions, that is, JA is specified for the device soldered on a circuit board.
ESD CAUTION
Rev. 0 | Page 5 of 16
AD8293G80/AD8293G160 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
-IN GND REF ADC OUT
1
AD8293Gxx
8
+IN +VS OUT FILT
07451-003
2
7
3
6
4
5
TOP VIEW (Not to Scale)
Figure 3. Pin Configuration
Table 6. Pin Function Descriptions
Pin No. 1 2 3 4 5 6 7 8 Mnemonic -IN GND REF ADC OUT FILT OUT +VS +IN Description Inverting Input Terminal (True Differential Input) Ground Reference Voltage Terminal (Drive This Terminal to Level-Shift the Output) Output with Series 5 k Resistor for Use with an Antialiasing Filter Place a capacitor across FILT and OUT to limit the amount of switching noise at the output (see Applications Information) Output Terminal Without Integrated Filter Positive Power Supply Terminal Noninverting Input Terminal (True Differential Input)
Rev. 0 | Page 6 of 16
AD8293G80/AD8293G160 TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25C, VCC = 5 V, and VREF = VCC/2; G = 80, C2 = 1300 pF, and C3 = 39 nF; G = 160, C2 = 680 pF, and C3 = 39 nF, unless otherwise specified.
60 VCC = 2.7V, 5V FILTER = 500Hz
60 G = 160 40
VCC = 2.7V, 5V FILTER = 10kHz
40 G = 160 20 G = 80 0
GAIN (dB)
GAIN (dB)
G = 80 20
0
-20
07451-004
100
1k FREQUENCY (Hz)
10k
100k
100
1k FREQUENCY (Hz)
10k
100k
Figure 4. Gain vs. Frequency
180 160 140 120
CMR (dB)
180 160 140 120
Figure 7. Gain vs. Frequency
VCC = 2.7V, 5V GAIN = 80, 160 FILTER = 500Hz
VCC = 2.7V, 5V GAIN = 80, 160 FILTER = 10kHz
100 80 60 40 20 10
CMR (dB)
100 80 60 40 20 10
100
1k FREQUENCY (Hz)
10k
100k
FREQUENCY (Hz)
Figure 5. Common-Mode Rejection (CMR) vs. Frequency
4 (0.02V, 3.3V)
INPUT COMMON-MODE VOLTAGE (V)
4
Figure 8. Common-Mode Rejection (CMR) vs. Frequency
(4.98V, 3.3V) VCC = 5V, VREF = VCC/2
INPUT COMMON-MODE VOLTAGE (V)
3
(0.02V, 3V)
(4.98V, 3V)
3
VCC = 5V, VREF = VCC/2 2 (0.02V, 1V) 1 VCC = 2.7V, VREF = VCC/2 (0.02V, 0V) -1 -1 0 1 2 3 4
2
(0.02V, 1V) 1
(2.68V, 1V)
(2.68V, 1V)
VCC = 2.7V, VREF = VCC/2 (2.68V, 0V) (0.02V, 0V) (4.98V, 0V)
0
0
(2.68V, 0V) (4.98V, 0V) 5 6
07451-019
0
1
2
3
4
5
6
07451-018
-1 -1
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
Figure 6. Input Common-Mode Voltage Range vs. Output Voltage, G = 80
Figure 9. Input Common-Mode Voltage Range vs. Output Voltage, G = 160
Rev. 0 | Page 7 of 16
07451-008
100
1k
10k
100k
07451-005
07451-007
-40 10
-20 10
AD8293G80/AD8293G160
10 POWER SUPPLY ON 5 0 -5 -10 -15 -20 -25 -0.2 GAIN = 160
10 POWER SUPPLY ON
INPUT OFFSET VOLTAGE (5mV/DIV)
4V OFFSET
INPUT OFFSET VOLTAGE (5mV/DIV)
5 4V OFFSET 0
-5
GAIN = 160 GAIN = 80
GAIN = 80
-10 VCC = 2.7V VCC = 5V 0 0.05 0.10 0.15 0.20
07451-012
07451-011
VCC = 2.7V VCC = 5V 0 0.2 0.4 0.6 TIME (ms) 0.8 1.0 1.2 1.4
07451-010
-15 -0.05
TIME (ms)
Figure 10. Input Offset Voltage vs. Turn-On Time, Filter = 500 Hz
1000
Figure 13. Input Offset Voltage vs. Turn-On Time, Filter = 10 kHz
NOISE (nV/ Hz)
100 GAIN = 160
GAIN = 80 10
0.1
1
10
100
1k
10k
100k
07451-009
TIME (10s/DIV)
FREQUENCY (Hz)
Figure 11. Voltage Noise Density
160 140 120
Figure 14. 0.01 Hz to 10 Hz Voltage Noise
0.30 0.25
VCC = 2.7V, 5V G = 80, 160
GAIN = 160
0.20 0.15 10kHz FILTER
50mV/DIV
PSR (dB)
100 GAIN = 80 80 60
0.10 0.05 0
-0.05
40 20 10 500Hz FILTER 10kHz FILTER 100 1k FREQUENCY (Hz) 10k 100k
07451-024
-0.10 -0.15
500Hz FILTER
1ms/DIV
Figure 12. Power Supply Rejection (PSR) vs. Frequency
Figure 15. Small Signal Step Response
Rev. 0 | Page 8 of 16
07451-025
1 0.01
VOLTAGE NOISE (200nV/DIV)
AD8293G80/AD8293G160
VCC = 2.7V G = 80, 160
VCC = 5V G = 80, 160
500mV/DIV
10kHz FILTER 1V/DIV 500Hz FILTER
07451-013
10kHz FILTER
500Hz FILTER
07451-017
1ms/DIV
1ms/DIV
Figure 16. Large Signal Step Response
Figure 17. Large Signal Step Response
Rev. 0 | Page 9 of 16
AD8293G80/AD8293G160 THEORY OF OPERATION
The AD8293G80/AD8293G160 are precision current-mode correction instrumentation amplifiers capable of single-supply operation. The current-mode correction topology results in excellent accuracy. Figure 18 shows a simplified diagram illustrating the basic operation of the AD8293G80/AD8293G160 (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 External Resistor R1, resulting in conversion of the input voltage to a signal current. Transistor M3 to Transistor M6 transfer twice this signal current to the inverting input of the op amp A1. Amplifier A1 and External Resistor R2 form a current-to-voltage converter to produce a rail-to-rail output voltage at 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 external reference voltage is applied to the noninverting input of A1 to set the output reference level. External Capacitor C2 is used to filter out correction noise.
HIGH PSR AND CMR
Common-mode rejection and power supply rejection 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 AD8293G80/AD8293G160 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). The parasitic resistance in series with R2 does not degrade CMR, but causes a small gain error and a very small offset error. Therefore, an external buffer amplifier is not required to drive VREF to maintain excellent CMR performance. This helps reduce system costs over conventional instrumentation amplifiers.
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 is seen effectively as a slowly varying offset error, which is reduced by the autocorrection topology of the AD8293G80/AD8293G160. This allows the AD8293G80/ AD8293G160 to have lower noise near dc than standard low noise instrumentation amplifiers.
VCC C2 I R1 I - IR1 IR1 = VINP M1 (VINP - VINN) R1 M2 VINN M3 M4 I M5 M6 I - IR1 I + IR1 VBIAS A1 VREF 2IR1 R3 C3
07451-020
R2
VOUT = VREF
+
2R2 R1
VINP - VINN
2I
2I
EXTERNAL
Figure 18. Simplified Schematic
Rev. 0 | Page 10 of 16
AD8293G80/AD8293G160 APPLICATIONS INFORMATION
OVERVIEW
The AD8293G80/AD8293G160 reduce board area by integrating filter components, such as Resistors R1, R2, and R3, as shown in Figure 19. Two outputs are available to the user: OUT (Pin 6) and ADC OUT (Pin 4). The difference between the two is the inclusion of a series 5 k resistor at ADC OUT. With the addition of an external capacitor, C3, ADC OUT forms a second filter, comprising of the 5 k resistor and C3, which can be used as an ADC antialiasing filter. In contrast, OUT is the direct output of the instrumentation amplifier. When using the antialiasing filter, there is slightly less switching ripple at ADC OUT than when obtaining the signal directly from OUT.
+5V 0.1F
7 5
+5V 0.1F
7 5
C2 OUTPUT
6
+VS
FILT R2
OUT
8
+IN R1 4k IN-AMP R3 5k ADC OUT
4
1
-IN
GND REF
2 3
AD8293Gxx
0.1F VOLTAGE REFERENCE
07451-022
1F
C2 680pF
0.1F
6
+VS +IN R1 4k
1
FILT R2 320k IN-AMP
OUT
Figure 20. Operating on a Single Supply Using an External Voltage Reference (The Output Can Be Used Without an Antialiasing Filter if the Signal Bandwidth Is <10 Hz)
OUTPUT TO ADC WITH ANTIALIASING FILTER ADC OUT
4
8
R3 5k
OUTPUT FILTERING
The output of the AD8293G80/AD8293G160 can be filtered to reduce switching ripple. Two filters can be used in conjunction to set the filter frequency. In the example that follows, two 700 Hz filters are used in conjunction to form a 500 Hz (recommended) bandwidth. Because the filter resistors are integrated in the AD8293G80/AD8293G160, only external capacitors are needed to set the filter frequencies. The primary filter is needed to limit the amount of switching noise at the output. Regardless of the output that is being used, OUT or ADC OUT, the primary filter comprising R2 and C2 must be implemented. The R2 value depends on the model; Table 7 shows the R2 value for each model. Table 7. Internal R2 Values
Model AD8293G80 AD8293G160 R2 (k) 160 320
-IN
C3 39nF
GND REF
2 3
AD8293G160
+5V
07451-021
100k
0.1F
100k
Figure 19. AD8293G160 with Antialiasing Filter and Level-Shifted Output (Using the Resistor Divider at the REF Pin, the Output Is Biased at 2.5 V)
REFERENCE CONNECTION
Unlike traditional 3-op-amp instrumentation amplifiers, parasitic resistance in series with REF (Pin 3) does not degrade CMR performance. The AD8293G80/AD8293G160 can attain extremely high CMR performance without the use of an external buffer amplifier to drive the REF pin, which is required by industrystandard instrumentation amplifiers. Reducing the need for buffer amplifiers to drive the REF pin helps to save valuable printed circuit board (PCB) space and minimizes system costs. For optimal performance in single-supply applications, REF should be set with a low noise precision voltage reference, such as the ADR44x (see Figure 20). However, for a lower system cost, the reference voltage can be set with a simple resistor voltage divider between the supply and GND (see Figure 19). This configuration results in degraded output offset performance if the resistors deviate from their ideal values. In dual-supply applications, VREF can simply be connected to GND. The REF pin current is approximately 10 pA, and as a result, an external buffer is not required.
The following equation results in the C2 value needed to set a 700 Hz primary filter. For a gain of 160, substitute R2 with 320 k; for a gain of 80, substitute R2 with 160 k. C2 = 1/(700 x 2 x x R2) Adding an external capacitor, C3, and measuring the output from ADC OUT further reduces the correction ripple. The internal 5 k resistor, labeled R3 in Figure 18, forms a low-pass filter with C3. This low-pass filter is the secondary filter. Set to 700 Hz, the secondary filter equation for C3 is as follows: C3 = 1/(700 x 2 x x 5 k)
Rev. 0 | Page 11 of 16
AD8293G80/AD8293G160
The addition of another single pole of 700 Hz on the output (from the secondary filter in Figure 18) is required for bandwidths greater than 10 Hz. These two filters, together, produce an overall bandwidth of 500 Hz. The internal resistors, R2 and R3, have an absolute tolerance of 20%. Table 8 lists the standard capacitors needed to create a filter with an overall bandwidth of 500 Hz. Table 8. Standard Capacitors Used to Form a Filter with an Overall Bandwidth of 500 Hz
Model AD8293G80 AD8293G160 C2 (pF) 1300 680 C3 (nF) 39 39
POWER SUPPLY BYPASSING
The AD8293G80/AD8293G160 use 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 the supply lines. This capacitor is necessary to minimize ripple from the correction clocks inside the IC. For dual-supply operation, a 0.1 F (ceramic) surface-mount capacitor should be connected from each supply pin to GND. For single-supply operation, a 0.1 F surface-mount capacitor should be connected from the supply line to GND. All bypass capacitors should be positioned as close to the DUT supply pins as possible, especially the bypass capacitor between the supplies. Placement of the bypass capacitor on the back of the board directly under the DUT is preferred.
For applications with low bandwidths (<10 Hz), only the primary filter is required. In such an event, the high frequency noise from the auto-zero amplifier (output amplifier) is not filtered before the following stage.
CLOCK FEEDTHROUGH
The AD8293G80/AD8293G160 use two synchronized clocks to perform the autocorrection. The input voltage-to-current amplifiers are corrected at 60 kHz. Trace amounts of these clock frequencies can be observed at the OUT pin. The amount of visible correction feedthrough is dependent on the values of the filters set by R2/C2. Use ADC OUT to create a filter using R3/C3 to further reduce correction feedthrough as described in the Output Filtering section.
INPUT OVERVOLTAGE PROTECTION
All terminals of the AD8293G80/AD8293G160 are protected against ESD. In the case of a dc overload voltage beyond either supply, a large current would flow directly through the ESD protection diodes. If such a condition can occur, an external resistor should be used in series with the inputs to limit current for voltages beyond the supply rails. The AD8293G80/AD8293G160 can safely handle 5 mA of continuous current, resulting in an external resistor selection of REXT = (VIN - VS)/5 mA
+5V C2 1.3nF
7 5 6
0.1F
+VS LOAD
8
FILT R2 160k IN-AMP
OUT
+IN R1 4k
I
RSHUNT
1
R3 5k ADC OUT
4
-IN
C3 39nF
ADC REF
1.8V DC-DC GND REF
2 3
+3.3V
AD8293G80
0.1F
10F
07451-023
Figure 21. Measuring Current Through a Shunt Resistor (Filter Is Set to 500 Hz)
Rev. 0 | Page 12 of 16
AD8293G80/AD8293G160 OUTLINE DIMENSIONS
2.90 BSC
8
7
6
5
1.60 BSC
1 2 3 4
2.80 BSC
PIN 1 INDICATOR 0.65 BSC 1.30 1.15 0.90 1.95 BSC
1.45 MAX 0.38 0.22
0.22 0.08 8 4 0
0.15 MAX
SEATING PLANE
0.60 0.45 0.30
COMPLIANT TO JEDEC STANDARDS MO-178-BA
Figure 22. 8-Lead Small Outline Transistor Package [SOT-23] (RJ-8) Dimensions shown in millimeters
ORDERING GUIDE
Model AD8293G80ARJZ-R2 1 AD8293G80ARJZ-R71 AD8293G80ARJZ-RL1 AD8293G80BRJZ-R21 AD8293G80BRJZ-R71 AD8293G80BRJZ-RL1 AD8293G160ARJZ-R21 AD8293G160ARJZ-R71 AD8293G160ARJZ-RL1 AD8293G160BRJZ-R21 AD8293G160BRJZ-R71 AD8293G160BRJZ-RL1
1
Gain 80 80 80 80 80 80 160 160 160 160 160 160
Temperature Range -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C
Package Description 8-Lead SOT-23 8-Lead SOT-23 8-Lead SOT-23 8-Lead SOT-23 8-Lead SOT-23 8-Lead SOT-23 8-Lead SOT-23 8-Lead SOT-23 8-Lead SOT-23 8-Lead SOT-23 8-Lead SOT-23 8-Lead SOT-23
Package Option RJ-8 RJ-8 RJ-8 RJ-8 RJ-8 RJ-8 RJ-8 RJ-8 RJ-8 RJ-8 RJ-8 RJ-8
Branding Y1H Y1H Y1H Y1N Y1N Y1N Y11 Y11 Y11 Y1K Y1K Y1K
Z = RoHS Compliant Part.
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AD8293G80/AD8293G160 NOTES
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AD8293G80/AD8293G160 NOTES
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AD8293G80/AD8293G160 NOTES
(c)2008 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D07451-0-8/08(0)
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