AD AD8479BRZ Very high common-mode voltage precision difference amplifier Datasheet

Very High Common-Mode Voltage
Precision Difference Amplifier
AD8479
Data Sheet
FEATURES
FUNCTIONAL BLOCK DIAGRAM
±600 V common-mode voltage range
Rail-to-rail output
Fixed gain of 1
Wide power supply range of ±2.5 V to ±18 V
550 μA typical power supply current
Excellent ac specifications
90 dB minimum CMRR
130 kHz bandwidth
High accuracy dc performance
5 ppm maximum gain nonlinearity
10 µV/°C maximum offset voltage drift
5 ppm/°C maximum gain drift
AD8479
REF(–) 1
+IN 3
1MΩ
NC
7
+VS
6
OUTPUT
5
REF(+)
1MΩ
–VS 4
NOTES
1. NC = NO CONNECT. DO NOT CONNECT TO THIS PIN.
11118-001
–IN 2
8
Figure 1.
APPLICATIONS
800
High voltage current sensing
Battery cell voltage monitors
Power supply current monitors
Motor controls
Isolation
VS = ±15V
The AD8479 is a difference amplifier with a very high input
common-mode voltage range. The AD8479 is a precision device
that allows the user to accurately measure differential signals in
the presence of high common-mode voltages up to ±600 V.
The AD8479 can replace costly isolation amplifiers in applications
that do not require galvanic isolation. The device operates over
a ±600 V common-mode voltage range and has inputs that are
protected from common-mode or differential mode transients
up to ±600 V.
400
VS = ±5V
200
0
–200
–400
–600
–800
–20
–15
–10
–5
0
VOUT (V)
5
10
15
20
11118-110
GENERAL DESCRIPTION
COMMON-MODE VOLTAGE (V)
600
Figure 2. Input Common-Mode Voltage vs. Output Voltage
The AD8479 has low offset voltage, low offset voltage drift,
low gain drift, low common-mode rejection drift, and excellent
common-mode rejection ratio (CMRR) over a wide frequency
range.
The AD8479 is available in a space-saving 8-lead SOIC package
and is operational over the −40°C to +125°C temperature range.
Rev. 0
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AD8479
Data Sheet
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications Information .............................................................. 12
Applications ....................................................................................... 1
Basic Connections ...................................................................... 12
General Description ......................................................................... 1
Single-Supply Operation ........................................................... 12
Functional Block Diagram .............................................................. 1
System-Level Decoupling and Grounding .............................. 12
Revision History ............................................................................... 2
Using a Large Shunt Resistor .................................................... 13
Specifications..................................................................................... 3
Output Filtering .......................................................................... 14
Absolute Maximum Ratings............................................................ 4
Gain of 60 Differential Amplifier ............................................. 14
ESD Caution .................................................................................. 4
Error Budget Analysis Example ............................................... 15
Pin Configuration and Function Descriptions ............................. 5
Outline Dimensions ....................................................................... 16
Typical Performance Characteristics ............................................. 6
Ordering Guide .......................................................................... 16
Theory of Operation ...................................................................... 11
REVISION HISTORY
4/13—Revision 0: Initial Version
Rev. 0 | Page 2 of 16
Data Sheet
AD8479
SPECIFICATIONS
VS = ±15 V, REF(−) = REF(+) = 0 V, RL = 2 kΩ, TA = 25°C, unless otherwise noted.
Table 1.
Parameter
GAIN
Nominal Gain
Gain Error
Gain Nonlinearity
Gain Drift
OFFSET VOLTAGE
Offset Voltage
Offset Voltage Drift
Power Supply Rejection
Ratio (PSRR)
INPUT
Common-Mode Rejection
Ratio (CMRR)
Operating Voltage Range
Input Operating
Impedance
Test Conditions/Comments
VOUT = ±10 V, RL = 2 kΩ
Min
TA = TMIN to TMAX
1
0.01
4
3
VS = ±15 V
VS = ±5 V
TA = TMIN to TMAX
VS = ±2.5 V to ±15 V
0.5
0.5
3
100
84
OUTPUT VOLTAGE NOISE
0.01 Hz to 10 Hz
Noise Spectral Density
POWER SUPPLY
Operating Voltage Range
Supply Current
TEMPERATURE RANGE
Specified Performance
Operational
Min
0.02
10
5
3
3
15
90
B Grade
Typ
Max
Unit
1
0.005
2
3
V/V
%
ppm
ppm/°C
0.5
0.5
3
100
0.01
5
5
1
1
10
mV
mV
µV/°C
dB
VCM = ±600 V dc
TA = 25°C
TA = TMIN to TMAX
VCM = 1200 V p-p, dc to 12 kHz
Common-mode
Differential
Common-mode
80
80
80
RL = 2 kΩ
90
90
90
80
96
500
500
dB
dB
dB
V
V
kΩ
2
2
MΩ
±600
±14.7
Differential
OUTPUT
Output Voltage Swing
Output Short-Circuit
Current
Capacitive Load
DYNAMIC RESPONSE
Small Signal −3 dB
Bandwidth
Slew Rate
Full Power Bandwidth
Settling Time
A Grade
Typ
Max
−VS + 0.3
Stable operation
+VS − 0.3
±600
±14.7
±55
−VS + 0.3
±55
+VS − 0.3
V
mA
500
500
pF
130
130
kHz
7.5
100
11
15.4
8
7.5
100
11
15.4
8
VOUT = 20 V p-p
0.01%, VOUT = 10 V step
0.001%, VCM = 10 V step
V/µs
kHz
µs
µs
30
1.6
35
30
1.6
35
f ≥ 100 Hz
µV p-p
μV/√Hz
±18
650
V
μA
μA
+85
+125
°C
°C
±2.5
VOUT = 0 V
TA = TMIN to TMAX
TA = TMIN to TMAX
550
850
−40
−40
Rev. 0 | Page 3 of 16
±18
650
±2.5
+85
+125
−40
−40
550
850
AD8479
Data Sheet
ABSOLUTE MAXIMUM RATINGS
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.
Table 2.
Parameter
Supply Voltage, VS
Input Voltage Range
Continuous
Common-Mode and Differential,
10 sec
Output Short-Circuit Duration
REF(−) and REF(+)
Maximum Junction Temperature
Operating Temperature Range
Storage Temperature Range
Lead Temperature (Soldering, 60 sec)
Rating
±18 V
±600 V
±900 V
Indefinite
−VS − 0.3 V to +VS + 0.3 V
150°C
−40°C to +125°C
−65°C to +150°C
300°C
ESD CAUTION
Rev. 0 | Page 4 of 16
Data Sheet
AD8479
REF(–) 1
–IN 2
AD8479
+IN 3
TOP VIEW
(Not to Scale)
–VS 4
8
NC
7
+VS
6
OUTPUT
5
REF(+)
NOTES
1. NC = NO CONNECT. DO NOT CONNECT TO THIS PIN.
Figure 3. Pin Configuration
Table 3. Pin Function Descriptions
Pin No.
1
2
3
4
5
6
7
8
Mnemonic
REF(−)
−IN
+IN
−VS
REF(+)
OUTPUT
+VS
NC
Description
Negative Reference Voltage Input.
Inverting Input.
Noninverting Input.
Negative Supply Voltage.
Positive Reference Voltage Input.
Output.
Positive Supply Voltage.
No Connect. Do not connect to this pin.
Rev. 0 | Page 5 of 16
11118-002
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
AD8479
Data Sheet
TYPICAL PERFORMANCE CHARACTERISTICS
VS = ±15 V, TA = 25°C, unless otherwise noted.
100
90
40
80
CMRR (dB)
50
30
70
20
60
10
50
0
–150
–100
50
0
–50
CMRR (µV/V)
100
40
1
10
100
1k
10k
100k
1M
FREQUENCY (Hz)
11118-006
N = 393
MEAN = –33.5249
SD = 30.5258
11118-003
HITS
60
Figure 7. CMRR vs. Frequency
Figure 4. CMRR Distribution
120
70
N = 395
MEAN = –29.0415
SD = 57.0658
100
60
+PSRR
80
PSRR (dB)
HITS
50
40
30
–PSRR
60
40
20
0
100
–100
GAIN ERROR (µV/V)
–200
200
300
11118-004
0
0.1
60
1k
10k
100k
1M
35
N = 377
MEAN = 344.277
SD = 1086.57
VS = ±15V
30
25
VOUT (V p-p)
40
30
20
15
20
10
10
5
–2000
0
2000
OFFSET VOLTAGE (µV)
4000
11118-005
HITS
100
Figure 8. PSRR vs. Frequency
50
0
–4000
10
FREQUENCY (Hz)
Figure 5. Gain Error Distribution
70
1
0
100
Figure 6. Offset Voltage Distribution
VS = ±5V
1k
10k
FREQUENCY (Hz)
100k
Figure 9. Large Signal Frequency Response
Rev. 0 | Page 6 of 16
1M
11118-008
0
–300
11118-007
20
10
Data Sheet
AD8479
150
10
VS = +5V, VREF = MIDSUPPLY
0
COMMON-MODE VOLTAGE (V)
–10
GAIN (dB)
100
–20
–30
–40
50
0
–50
1k
10k
100k
1M
10M
FREQUENCY (Hz)
–100
11118-009
–60
100
0
Figure 10. Small Signal Frequency Response
0.5
1.0
1.5
2.0
2.5
3.0
VOUT (V)
3.5
4.0
4.5
5.0
11118-112
–50
Figure 13. Input Common-Mode Voltage vs. Output Voltage, Single Supply,
VS = +5 V, VREF = Midsupply
800
VS = ±15V
COMMON-MODE VOLTAGE (V)
600
400
VS = ±5V
5V/DIV
200
11.0µs TO 0.01%
15.4µs TO 0.001%
0
–200
0.002%/DIV
–400
–15
–10
–5
0
VOUT (V)
5
10
15
20
11118-110
–800
–20
11118-113
–600
TIME (10µs/DIV)
Figure 11. Input Common-Mode Voltage vs. Output Voltage, Dual Supplies,
VS = ±15 V, ±5 V
Figure 14. Settling Time
250
20
VS = +5V, VREF = 0V
10
150
5
VOUT (V)
COMMON-MODE VOLTAGE (V)
RL = 2kΩ
CL = 1000pF
15
200
100
0
–5
50
–10
0
0
0.5
1.0
1.5
2.0
2.5
3.0
VOUT (V)
3.5
4.0
4.5
5.0
Figure 12. Input Common-Mode Voltage vs. Output Voltage, Single Supply,
VS = +5 V, VREF = 0 V
Rev. 0 | Page 7 of 16
–20
–8
11118-114
–50
11118-111
–15
–4
0
4
8
12
16
20
24
TIME (µs)
Figure 15. Large Signal Pulse Response
28
32
AD8479
Data Sheet
200
10
150
GAIN ERROR (µV/V)
15
0
–40°C
+25°C
+85°C
+105°C
+125°C
–10
–15
100
1k
10k
100k
100
50
0
–50
1M
RESISTANCE (Ω)
–100
–40
–25
–10
5
20
35
50
65
80
95
110
125
8
10
TEMPERATURE (°C)
11118-118
–5
11118-014
VOUT (V)
5
Figure 19. Gain Drift
Figure 16. Output Voltage vs. Load over Temperature
15
20
15
10
NONLINEARITY (ppm)
10
0
–40°C
+25°C
+85°C
+105°C
+125°C
–10
5
10
0
–5
–10
–15
–15
0
5
15
20
25
30
35
40
45
ILOAD (mA)
–20
–10
–8
–6
–4
–2
0
2
4
6
VOUT (V)
Figure 17. Output Voltage vs. Output Current over Temperature
11118-019
–5
11118-015
VOUT (V)
5
Figure 20. Gain Nonlinearity
30
8
NORMALIZED AT 25°C
REPRESENTATIVE DATA
NORMALIZED AT 0V; OFFSET TO SHOW
DIFFERENT POWER SUPPLIES
6
20
–10
0
–2
VS = ±18V
VS = ±15V
VS = ±12V
VS = ±10V
VS = ±5V
–4
–20
–6
–30
–40
–25
–10
5
20
35
50
65
TEMPERATURE (°C)
80
95
110
125
–8
–20
11118-117
CMRR (µV/V)
0
2
Figure 18. CMRR vs. Temperature, VCM = ±20 V
–16
–12
–8
–4
0
4
VOUT (V)
8
12
16
Figure 21. Output Error vs. Output Voltage, RL = 10 kΩ
Rev. 0 | Page 8 of 16
20
11118-020
OUTPUT ERROR (mV)
4
10
Data Sheet
AD8479
6
8
NORMALIZED AT 0V; OFFSET TO SHOW
DIFFERENT POWER SUPPLIES
6
4
2
VOUT (mV)
2
0
0
–2
–16
–12
–8
–4
0
4
8
12
16
–4
20
VOUT (V)
–6
–10
–5
5
10
15
20
25
30
6
NORMALIZED AT 0V; OFFSET TO SHOW
DIFFERENT POWER SUPPLIES
CL = 470pF
CL = 670pF
CL = 1.00nF
CL = 1.20nF
CL = 1.47nF
CL = 1.67nF
4
4
2
VOUT (mV)
2
0
0
–2
–16
–12
–8
–4
0
4
8
12
16
–4
20
VOUT (V)
–6
–10
0
5
10
15
20
25
30
35
40
45
50
TIME (µs)
Figure 26. Small Signal Pulse Response vs. Capacitive Load
Figure 23. Output Error vs. Output Voltage, RL = 1 kΩ
60
4
VS = ±5V
RL = 10kΩ
2
RL = 2kΩ
1
RL = 1kΩ
0
–4
–3
–2
–1
0
1
2
3
4
5
VOUT (V)
6
20
0
–20
–40
–60
–40
11118-023
–5
40
–ISC
–25
–10
5
20
35
50
65
80
95
110
TEMPERATURE (°C)
Figure 24. Output Error vs. Output Voltage, VS = ±5 V
Figure 27. Short-Circuit Current vs. Temperature
Rev. 0 | Page 9 of 16
125
11118-027
SHORT-CIRCUIT CURRENT (mA)
+ISC
3
–1
–6
–5
11118-026
–6
–8
–20
–2
VS = ±18V
VS = ±15V
VS = ±12V
VS = ±10V
VS = ±5V
–4
11118-022
OUTPUT ERROR (mV)
40
Figure 25. Small Signal Pulse Response
6
OUTPUT ERROR (mV)
35
TIME (µs)
Figure 22. Output Error vs. Output Voltage, RL = 2 kΩ
8
0
11118-025
–6
–8
–20
–2
VS = ±18V
VS = ±15V
VS = ±12V
VS = ±10V
VS = ±5V
–4
11118-021
OUTPUT ERROR (mV)
4
AD8479
Data Sheet
10
+SR
SLEW RATE (V/µs)
6
4
2
0
–2
–4
–6
–8
–10
–40
–25
–10
5
20
35
50
65
80
95
110
125
TEMPERATURE (°C)
11118-028
–SR
VS = ±15V
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
1
10
100
1k
10k
100k
FREQUENCY (Hz)
Figure 31. Voltage Noise Spectral Density vs. Frequency
Figure 28. Slew Rate vs. Temperature
600
580
540
NOISE (20µV/DIV)
SUPPLY CURRENT (µA)
560
520
500
480
460
440
2
4
6
8
10
12
14
16
18
SUPPLY VOLTAGE (±V)
Figure 32. 0.1 Hz to 10 Hz Noise
Figure 29. Supply Current vs. Supply Voltage
1000
900
VS = ±15V
VS = ±12V
VS = ±5V
600
500
400
300
200
100
0
–40
–25
–10
5
20
35
50
65
80
95
TEMPERATURE (°C)
110
125
11118-030
SUPPLY CURRENT (µA)
800
700
TIME (1s/DIV)
Figure 30. Supply Current vs. Temperature
Rev. 0 | Page 10 of 16
11118-032
400
11118-029
420
11118-031
8
VOLTAGE NOISE SPECTRAL DENSITY (µV/√Hz)
3.0
Data Sheet
AD8479
THEORY OF OPERATION
The AD8479 is a unity-gain, differential-to-single-ended
amplifier that can reject extremely high common-mode signals
in excess of 600 V with 15 V supplies. The AD8479 consists of
an operational amplifier (op amp) and a resistor network (see
Figure 33).
The complete transfer function is
AD8479
REF(–) 1
+IN 3
–VS 4
1MΩ
8
NC
7
+VS
6
OUTPUT
VOUT = V (+IN) − V (−IN)
Laser wafer-trimming provides resistor matching so that
common-mode signals are rejected and differential input
signals are amplified.
1MΩ
5
REF(+)
NOTES
1. NC = NO CONNECT. DO NOT CONNECT TO THIS PIN.
Figure 33. Functional Block Diagram
11118-033
–IN 2
To achieve the high common-mode voltage range, an internal
resistor divider—connected to Pin 3 and Pin 5—attenuates the
noninverting signal by a factor of 60. The internal resistors at
Pin 1 and Pin 2, as well as the feedback resistor, restore the gain
to provide a differential gain of unity.
To reduce output voltage drift, the op amp uses super beta transistors in its input stage. The input offset current and its associated
temperature coefficient contribute no appreciable output voltage
offset or drift, which has the added benefit of reducing voltage
noise because the corner where 1/f noise becomes dominant is
below 5 Hz. To reduce the dependence of gain accuracy on the
op amp, the open-loop voltage gain of the op amp exceeds
20 million V/V, and the PSRR exceeds 90 dB.
Rev. 0 | Page 11 of 16
AD8479
Data Sheet
APPLICATIONS INFORMATION
BASIC CONNECTIONS
1
RSHUNT
7
3
6
+VS
0.1µF
+IN
–VS
(SEE
TEXT)
2
NC
4
5
(SEE
TEXT)
VOUT = ISHUNT × RSHUNT
REF(+)
0.1µF
NC = NO CONNECT
–VS
–2.5V TO –18V
11118-034
ISHUNT
8
7
VX
+VS
0.1µF
+IN
3
6
VY
–VS
4
5
REF(+)
OUTPUT = VOUT – VREF
NC = NO CONNECT
VREF
Figure 34. Basic Connections
The differential input signal, which typically results from a
load current flowing through a small shunt resistor, is applied to
Pin 2 and Pin 3 with the polarity shown in Figure 34 to obtain a
positive gain. The common-mode voltage on the differential
input signal can range from −600 V to +600 V, and the maximum
differential voltage is ±14.7 V. When configured as shown in
Figure 34, the device operates as a simple gain-of-1, differentialto-single-ended amplifier; the output voltage is the shunt resistance
times the shunt current. The output is measured with respect to
Pin 1 and Pin 5.
Pin 1 and Pin 5 (REF(−) and (REF(+)) should be grounded for a
gain of unity and should be connected to the same low impedance
ground plane. Failure to do this results in degraded common-mode
rejection. Pin 8 is a no connect pin and should be left open.
When the AD8479 is operated with a single supply and a
reference voltage is applied to REF(+) and REF(−), the input
common-mode voltage range of the AD8479 is reduced. The
reduced input common-mode range depends on the voltage at
the inverting and noninverting inputs of the internal op amp,
labeled VX and VY in Figure 35. These nodes can swing to within
1 V of either rail. Therefore, for a single supply voltage of 10 V,
VX and VY can have a value from 1 V to 9 V. If VREF is set to 5 V,
the allowable common-mode voltage range is +245 V to −235 V.
The common-mode voltage range can be calculated as follows:
VCM(±) = 60 × (VX or VY(±)) − (59 × VREF)
SYSTEM-LEVEL DECOUPLING AND GROUNDING
The use of ground planes is recommended to minimize the
impedance of ground returns and, therefore, the size of dc errors.
Figure 36 shows how to use grounding in a mixed-signal environment, that is, with digital and analog signals present. To isolate
low level analog signals from a noisy digital environment, many
data acquisition components have separate analog and digital
ground returns. All ground pins from mixed-signal components,
such as ADCs, should return through a low impedance analog
ground plane. Digital ground lines of mixed-signal converters
should also be connected to the analog ground plane.
ANALOG POWER
SUPPLY
–5V
+5V
GND
SINGLE-SUPPLY OPERATION
DIGITAL
POWER SUPPLY
GND +5V
0.1µF
Figure 35 shows the connections for operating the AD8479 with
a single supply. Because the output can swing to within only about
0.3 V of either rail, an offset must be applied to the output. This
offset can be applied by connecting REF(+) and REF(−) to a low
impedance reference voltage that is capable of sinking current
(some ADCs provide this voltage as an output). Therefore, for a
single supply of 10 V, VREF can be set to 5 V for a bipolar input
signal, allowing the output to swing ±9.4 V around the central
5 V reference voltage. For unipolar input signals, VREF can be set
to approximately 1 V, allowing the output to swing from 1 V (for
a 0 V input) to within 0.3 V of the positive rail.
0.1µF
0.1µF 0.1µF
4
7
–VS
+IN
3
–IN
2
AD8479
+VS
OUTPUT 6
REF(–) REF(+)
1
5
VDD AGND DGND
VIN1
ADC
12
GND
VDD
MICROPROCESSOR
VIN2
Figure 36. Optimal Grounding Practice for a Dual Supply Environment
with Separate Analog and Digital Supplies
Rev. 0 | Page 12 of 16
11118-036
–IN
1
2
NC
Figure 35. Operation with a Single Supply
+VS
+2.5V TO +18V
AD8479
REF(–)
–IN
RSHUNT
ISHUNT
8
11118-035
Figure 34 shows the basic connections for operating the
AD8479 with a dual supply. A supply voltage from ±2.5 V to
±18 V is applied across Pin 7 and Pin 4. Both supplies should be
decoupled close to the pins using 0.1 μF capacitors. Electrolytic
capacitors of 10 μF, also located close to the supply pins, may be
required if low frequency noise is present on the power supply.
Although multiple amplifiers can be decoupled by a single set of
10 μF capacitors, each AD8479 should have its own set of 0.1 μF
capacitors so that the decoupling point can be located directly at
the IC power pins.
+VS
AD8479
REF(–)
Data Sheet
AD8479
Typically, analog and digital grounds should be separated. At
the same time, however, the voltage difference between digital
and analog grounds on a converter must also be minimized to
keep this difference as small as possible (typically <0.3 V). The
increased noise—caused by the digital return currents of the
converter flowing through the analog ground plane—is typically
negligible.
USING A LARGE SHUNT RESISTOR
The insertion of a large value shunt resistor across the input pins,
Pin 2 and Pin 3, unbalances the input resistor network, thereby
introducing common-mode error. The magnitude of the error
depends on the common-mode voltage and the magnitude of
the shunt resistor (RSHUNT).
Table 4 shows some sample error voltages generated by a
common-mode voltage of 600 V dc with shunt resistors from
20 Ω to 2000 Ω. Assuming that the shunt resistor is selected to
use the full ±10 V output swing of the AD8479, the error voltage
becomes quite significant as the value of RSHUNT increases.
Maximum isolation between analog and digital signals is
achieved by connecting the ground planes back to the supplies.
Note that Figure 36 suggests a star ground system for the analog
circuitry, with all ground lines connected, in this case, to the
analog ground of the ADC. However, when ground planes are
used, it is sufficient to connect ground pins to the nearest point
on the low impedance ground plane.
Table 4. Error Resulting from Large Values of RSHUNT
(Uncompensated Circuit)
RSHUNT (Ω)
20
1000
2000
If only one power supply is available, it must be shared by both
digital and analog circuitry. Figure 37 shows how to minimize
interference between the digital and analog circuitry. In Figure 37,
the reference of the ADC is used to drive the REF(+) and REF(−)
pins of the AD8479. This means that the reference must be capable
of sourcing and sinking a current equal to VCM/500 kΩ.
Error VOUT (V)
0.012
0.583
1.164
To measure low current or current near zero in a high commonmode voltage environment, an external resistor equal to the shunt
resistor value can be added to the low impedance side of the shunt
resistor, as shown in Figure 38.
0.1µF
0.1µF
0.1µF
–IN
2
+VS
AD8479
VDD
–VS
OUTPUT 6
REF(–) REF(+)
1
5
VIN1
AGND DGND
ADC
VDD
GND
ISHUNT
RCOMP
–IN
RSHUNT
+IN
MICROPROCESSOR
VIN2
11118-037
+IN
3
4
VREF
Figure 37. Optimal Grounding Practice for a Single-Supply Environment
As in the dual-supply environment, separate analog and digital
ground planes should be used (although reasonably thick traces
can be used as an alternative to a digital ground plane). These
ground planes should connect at the ground pin of the power
supply. Separate traces (or power planes) should run from the
power supply to the supply pins of the digital and analog circuits.
Ideally, each device should have its own power supply trace, but
these traces can be shared by a number of devices, as long as a
single trace is not used to route current to both digital and
analog circuitry.
Rev. 0 | Page 13 of 16
–VS
–VS
0.1µF
+VS
AD8479
REF(–)
1
8
2
7
3
6
4
5
NC
0.1µF
+VS
VOUT
REF(+)
NC = NO CONNECT
Figure 38. Compensating for Large Shunt Resistors
11118-038
POWER SUPPLY
GND
+5V
7
Error Indicated (mA)
0.6
0.6
0.6
AD8479
Data Sheet
OUTPUT FILTERING
GAIN OF 60 DIFFERENTIAL AMPLIFIER
To limit noise at the output, a simple two-pole, low-pass Butterworth filter can be implemented using the ADA4077-2 after the
AD8479, as shown in Figure 39.
Low level signals can be connected directly to the −IN and +IN
inputs of the AD8479. Differential input signals can also be connected to give a precise gain of 60 (see Figure 40); however, large
common-mode voltages are no longer permissible. Cold junction
compensation can be implemented using a temperature sensor,
such as the AD590.
+VS
8
1
NC
C1
0.1µF
–IN
7
2
+VS
ADA4077-2
R1
+IN
3
0.1µF
+VS
6
R2
0.1µF
THERMOCOUPLE
C2
5
4
0.1µF
–IN
REF(+)
1
8
2
7
3
6
4
5
NC
+VS
–VS
0.1µF
+IN
11118-039
–VS
+VS
AD8479
REF(–)
VOUT
NC = NO CONNECT
VOUT
VREF
Figure 39. Filtering Output Noise Using a Two-Pole Butterworth Filter
Table 5 provides recommended component values for various
corner frequencies, along with the peak-to-peak output noise
for each case.
REF(+)
NC = NO CONNECT
11118-041
AD8479
REF(–)
Figure 40. Gain of 60 Thermocouple Amplifier
Table 5. Recommended Values for Two-Pole Butterworth Filter
Corner Frequency
50 kHz
5 kHz
500 Hz
50 Hz
No Filter
R1
2.94 kΩ ± 1%
2.94 kΩ ± 1%
2.94 kΩ ± 1%
2.7 kΩ ± 10%
R2
1.58 kΩ ± 1%
1.58 kΩ ± 1%
1.58 kΩ ± 1%
1.58 kΩ ± 10%
C1
2.2 nF ± 10%
22 nF ± 10%
220 nF ± 10%
2.2 µF ± 20%
Rev. 0 | Page 14 of 16
C2
1 nF ± 10%
10 nF ± 10%
0.1 µF ± 10%
0.1 µF ± 20%
Output Noise (p-p)
2.9 mV
0.9 mV
0.296 mV
0.095 mV
4.7 mV
Data Sheet
AD8479
The calculations in Table 6 assume an induced noise level of
1 V p-p at 60 Hz on the lead wires, in addition to a full-scale dc
differential voltage of 10 V. The error budget table quantifies the
contribution of each error source. Note that the dominant error
source in this example is due to the dc common-mode voltage.
ERROR BUDGET ANALYSIS EXAMPLE
In the dc application described in this section, the 10 A output
current from a device with a high common-mode voltage (such
as a power supply or current-mode amplifier) is sensed across a
1 Ω shunt resistor (see Figure 41). The common-mode voltage is
600 V, and the resistor terminals are connected through a long
pair of lead wires located in a high noise environment, for example,
50 Hz/60 Hz, 440 V ac power lines.
OUTPUT
CURRENT
AD8479
REF(–)
10A
600V CMDC
TO GROUND
–IN
1
8
2
7
NC
+VS
0.1µF
1Ω
SHUNT
+IN
–VS
6
4
5
VOUT
REF(+)
11118-042
60Hz
POWER LINE
3
0.1µF
NC = NO CONNECT
Figure 41. Error Budget Analysis Example: VIN = 10 V Full Scale, VCM = 600 V DC,
RSHUNT = 1 Ω, 1 V p-p, 60 Hz Power Line Interference
Table 6. Error Budget Analysis Example (VCM = 600 V DC)
Error Source
ACCURACY, TA = 25°C
Initial Gain Error
Offset Voltage
DC CMR (Over Temperature)
TEMPERATURE DRIFT (85°C)
Gain Drift
Offset Voltage Drift
RESOLUTION
Noise, Typical, 0.01 Hz to 10 Hz, μV p-p
CMR, 60 Hz
Nonlinearity
Calculation of Error
Error (ppm of FS)
(0.0001 × 10)/10 V × 106
(0.001 V/10 V) × 106
(32 × 10−6 × 600 V)/10 V × 106
Total Accuracy Error
100
100
1920
2120
5 ppm/°C × 60°C
(10 μV/°C × 60°C) × 106/10 V
Total Temperature Drift Error
300
60
360
35 μV/10 V × 106
(32 × 10−6 × 1 V)/10 V × 106
(5 × 10−6 × 10 V)/10 V × 106
Total Resolution Error
Total Error
4
3
5
12
2492
Rev. 0 | Page 15 of 16
AD8479
Data Sheet
OUTLINE DIMENSIONS
5.00 (0.1968)
4.80 (0.1890)
1
5
6.20 (0.2441)
5.80 (0.2284)
4
1.27 (0.0500)
BSC
0.25 (0.0098)
0.10 (0.0040)
COPLANARITY
0.10
SEATING
PLANE
1.75 (0.0688)
1.35 (0.0532)
0.51 (0.0201)
0.31 (0.0122)
0.50 (0.0196)
0.25 (0.0099)
45°
8°
0°
0.25 (0.0098)
0.17 (0.0067)
1.27 (0.0500)
0.40 (0.0157)
COMPLIANT TO JEDEC STANDARDS MS-012-AA
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.
012407-A
8
4.00 (0.1574)
3.80 (0.1497)
Figure 42. 8-Lead Standard Small Outline Package [SOIC_N]
Narrow Body
(R-8)
Dimensions shown in millimeters and (inches)
ORDERING GUIDE
Model 1
AD8479ARZ
AD8479ARZ-RL
AD8479BRZ
AD8479BRZ-RL
1
Temperature Range
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
Package Description
8-Lead SOIC_N
8-Lead SOIC_N, 13-Inch Tape and Reel, 2,500 pieces
8-Lead SOIC_N
8-Lead SOIC_N, 13-Inch Tape and Reel, 2,500 pieces
Z = RoHS Compliant Part.
©2013 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D11118-0-4/13(0)
Rev. 0 | Page 16 of 16
Package Option
R-8
R-8
R-8
R-8