INTERSIL EL8171

EL8171, EL8172
®
Data Sheet
July 27, 2009
Micropower, Single Supply, Rail-to-Rail
Input-Output Instrumentation Amplifiers
The EL8171 and EL8172 are micropower instrumentation
amplifiers optimized for single supply operation over the
+2.4V to +5.5V range. Inputs and outputs can operate
rail-to-rail. As with all instrumentation amplifiers, a pair of
inputs provide very high common-mode rejection and are
completely independent from a pair of feedback terminals.
The feedback terminals allow zero input to be translated to
any output offset, including ground. A feedback divider
controls the overall gain of the amplifier.
The EL8172 is compensated for a gain of 100 or more, and
the EL8171 is compensated for a gain of 10 or more. The
EL8171 and EL8172 have PMOS input devices that provide
sub-nA input bias currents.
The amplifiers can be operated from one lithium cell or two
Ni-Cd batteries. The EL8171 and EL8172 input range goes
from below ground to slightly above positive rail. The output
stage swings completely to ground (ground sensing) or
positive supply - no pull-up or pull-down resistors are
needed.
FN6293.5
Features
• 95µA maximum supply current
• Maximum input offset voltage
- 300µV (EL8172)
- 1500µV (EL8171)
• 50pA maximum input bias current
• 450kHz -3dB bandwidth (G = 10)
• 170kHz -3dB bandwidth (G = 100)
• Single supply operation
- Input voltage range is rail-to-rail
- Output swings rail-to-rail
- Ground sensing
• Pb-free (RoHS compliant)
Applications
• Battery- or solar-powered systems
• Strain gauges
• Current monitors
• Thermocouple amplifiers
Pinout
EL8171, EL8172
(8 LD SOIC)
TOP VIEW
DNC 1
IN- 2
+
+
Σ
IN+ 3
8 FB+
7 V+
6 VOUT
V- 4
5 FB-
1
Ordering Information
PART
NUMBER
(Note)
PART
MARKING
PACKAGE
(Pb-free)
PKG.
DWG. #
EL8171FSZ*
8171FSZ
8 Ld SOIC
MDP0027
EL8172FSZ*
8172FSZ
8 Ld SOIC
MDP0027
*Add “-T7” suffix for tape and reel. Please refer to TB347 for details
on reel specifications.
NOTE: These Intersil Pb-free plastic packaged products employ
special Pb-free material sets, molding compounds/die attach
materials, and 100% matte tin plate plus anneal (e3 termination
finish, which is RoHS compliant and compatible with both SnPb and
Pb-free soldering operations). Intersil Pb-free products are MSL
classified at Pb-free peak reflow temperatures that meet or exceed
the Pb-free requirements of IPC/JEDEC J STD-020.
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc.
Copyright © Intersil Americas Inc. 2005-2007, 2009. All Rights Reserved.
All other trademarks mentioned are the property of their respective owners.
EL8171, EL8172
Absolute Maximum Ratings (TA = +25°C)
Thermal Information
Supply Voltage, V+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5V
Differential Input Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5mA
Differential Input Voltage (EL8172) . . . . . . . . . . . . . . . . . . . . . . 0.5V
Differential Input Voltage (EL8171) . . . . . . . . . . . . . . . . . . . . . . 1.0V
ESD Rating
Human Body Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3kV
Thermal Resistance
θJA (°C/W)
8 Ld SOIC Package . . . . . . . . . . . . . . . . . . . . . . . .
122
Output Short-Circuit Duration . . . . . . . . . . . . . . . . . . . . . . .Indefinite
Ambient Operating Temperature . . . . . . . . . . . . . . .-40°C to +125°C
Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . .-65°C to +150°C
Pb-Free Reflow Profile. . . . . . . . . . . . . . . . . . . . . . . . .see link below
http://www.intersil.com/pbfree/Pb-FreeReflow.asp
CAUTION: Do not operate at or near the maximum ratings listed for extended periods of time. Exposure to such conditions may adversely impact product reliability and
result in failures not covered by warranty.
IMPORTANT NOTE: All parameters having Min/Max specifications are guaranteed. Typical values are for information purposes only. Unless otherwise noted, all tests
are at the specified temperature and are pulsed tests, therefore: TJ = TC = TA
Electrical Specifications
PARAMETER
V+ = +5V, V- = GND, VCM = 1/2V+, RL = Open, TA = +25°C, unless otherwise specified. Boldface limits apply
over the operating temperature range, -40°C to +125°C.
DESCRIPTION
CONDITIONS
MIN
(Note 1)
TYP
MAX
(Note 1)
UNIT
DC SPECIFICATIONS
VOS
TCVOS
Input Offset Voltage
Input Offset Voltage Temperature
Coefficient
EL8171
-1.5
-2
±0.47
1.5
2
mV
EL8172
-0.3
-0.7
±0.07
0.3
0.7
mV
EL8171
1.5
µV/°C
EL8172
0.14
µV/°C
IOS
Input Offset Current, ± IN, ± FB
-25
-500
±4
25
500
pA
pA
IB
Input Bias Current
-50
-4
±10
50
4
pA
nA
VIN
Input Voltage Range
Guaranteed by CMRR test
0
5
V
CMRR
Common Mode Rejection Ratio
VCM = 0V to +5V
75
100
dB
PSRR
Power Supply Rejection Ratio
EL8171, V+ = 2.4V to 5V
75
90
dB
EL8172, V+ = 2.4V to 5V
75
100
dB
EL8171, RL = 100kΩ to 2.5V
-0.7
±0.15
0.7
%
EL8172, RL = 100kΩ to 2.5V
-1
-1.5
±0.2
+1
1.5
%
%
4
10
10
mV
mV
0.13
0.2
0.25
V
V
EG
VOUT
Gain Error
Maximum Voltage Swing
Output low, 100kΩ to 2.5V
Output low, 1kΩ to 2.5V
Output high, 100kΩ to 2.5V
4.985
4.980
4.996
V
V
Output high, 1kΩ to GND
4.860
4.750
4.87
V
V
45
38
65
IS
Supply Current
VSUPPLY
Supply Operating Range
V+ to V-
2.4
IO+
Output Source Current into 10Ω to V+/2 V+ = 5V
23
19
32
mA
6
4.5
8
mA
V+ = 2.4V
2
95
110
µA
5.5
V
FN6293.5
July 27, 2009
EL8171, EL8172
Electrical Specifications
PARAMETER
IO-
V+ = +5V, V- = GND, VCM = 1/2V+, RL = Open, TA = +25°C, unless otherwise specified. Boldface limits apply
over the operating temperature range, -40°C to +125°C. (Continued)
DESCRIPTION
Output Sink Current into 10Ω to V+/2
CONDITIONS
MIN
(Note 1)
TYP
MAX
(Note 1)
UNIT
V+ = 5V
19
15
26
mA
V+ = 2.4V
5
4
7
mA
Gain = 10V/V
450
kHz
Gain = 20
210
kHz
Gain = 50
66
kHz
Gain = 100
33
kHz
Gain = 100
170
kHz
Gain = 200
70
kHz
Gain = 500
25
kHz
Gain = 1000
12
kHz
f = 0.1Hz to 10Hz
14
µVP-P
10
µVP-P
220
nV/√Hz
EL8172
80
nV/√Hz
EL8171, fo = 1kHz
0.9
pA/√Hz
EL8172, fo = 1kHz
0.2
pA/√Hz
EL8171
85
dB
100
dB
90
dB
92
dB
97
dB
92
dB
AC SPECIFICATIONS
-3dB BW
-3dB Bandwidth
EL8171
EL8172
eN
Input Noise Voltage
EL8171
EL8172
Input Noise Voltage Density
iN
Input Noise Current Density
CMRR @ 60Hz Input Common Mode Rejection Ratio
EL8171
EL8172
PSRR+ @
120Hz
Power Supply Rejection Ratio (V+)
PSRR- @
120Hz
Power Supply Rejection Ratio (V-)
EL8171
EL8172
EL8171
EL8172
fo = 1kHz
VCM = 1VPP,
RL = 10kΩ to VCM
V+, V- = ±2.5V,
VSOURCE = 1VPP,
RL = 10kΩ to VCM
V+, V- = ±2.5V,
VSOURCE = 1VPP,
RL = 10kΩ to VCM
TRANSIENT RESPONSE
SR
RL = 1kΩ to GND
Slew Rate
0.4
0.35
0.55
0.7
0.7
V/µs
NOTES:
1. Parameters with MIN and/or MAX limits are 100% tested at +25°C, unless otherwise specified. Temperature limits established by characterization
and are not production tested.
3
FN6293.5
July 27, 2009
EL8171, EL8172
Typical Performance Curves V+ = 5V, V- = 0V,VCM = 2.5V, RL = Open, unless otherwise specified.
70
90
COMMON-MODE INPUT = 1/2V+
60
COMMON-MODE INPUT = 1/2V+
GAIN = 10,000
GAIN = 1000
80
GAIN = 500
GAIN = 5,000
GAIN = 200
GAIN (dB)
GAIN (dB)
50
GAIN = 100
40
GAIN = 50
30
10
GAIN = 10
1
10
GAIN = 2,000
GAIN = 1,000
60
GAIN = 500
50
GAIN = 20
20
70
GAIN = 200
GAIN = 100
40
100
1k
10k
FREQUENCY (Hz)
100k
30
1M
1
FIGURE 1. EL8171 FREQUENCY RESPONSE vs CLOSED
LOOP GAIN
10
100
1k
10k
FREQUENCY (Hz)
100k
1M
FIGURE 2. EL8172 FREQUENCY RESPONSE vs CLOSED
LOOP GAIN
25
45
40
20
V+ = 5V
35
V+ = 5V
10
5
0
GAIN (dB)
GAIN (dB)
30
15
V+ = 2.4V
AV = 10
RL = 10kΩ
CL = 10pF
RF/RG = 10
RF = 1kΩ
RG = 100Ω
10
100
20
15
10
5
1k
10k
100k
V+ = 2.4V
25
0
1M
AV = 100
RL = 10kΩ
CL = 10pF
RF/RG = 100
RF = 10kΩ
RG = 100Ω
10
100
FREQUENCY (Hz)
1k
10k
100k
1M
FREQUENCY (Hz)
FIGURE 3. EL8171 FREQUENCY RESPONSE vs SUPPLY
VOLTAGE
FIGURE 4. EL8172 FREQUENCY RESPONSE vs SUPPLY
VOLTAGE
50
25
820pF
470pF
2200pF
45
20
15
10
5
100pF
AV = 10
R = 10kΩ
CL = 10pF
RF/RG = 10
RF = 10kΩ
RG = 100Ω
10
100
GAIN (dB)
GAIN (dB)
1200pF
220pF
40
35
30
25
1k
10k
100k
1M
FREQUENCY (Hz)
FIGURE 5. EL8171 FREQUENCY RESPONSE vs CLOAD
4
820pF
56pF
AV = 10
R = 10kΩ
CL = 10pF
RF/RG = 10
RF = 10kΩ
RG = 100Ω
10
100
1k
10k
100k
1M
FREQUENCY (Hz)
FIGURE 6. EL8172 FREQUENCY RESPONSE vs CLOAD
FN6293.5
July 27, 2009
EL8171, EL8172
Typical Performance Curves V+ = 5V, V- = 0V,VCM = 2.5V, RL = Open, unless otherwise specified. (Continued)
120
90
80
100
70
CMRR (dB)
CMRR (dB)
60
50
40
AV = 10
30
80
60
AV = 100
40
20
10
20
0
-10
10
100
1k
10k
100k
0
10
1M
100
120
120
100
100
80
PSRR+
PSRR (dB)
PSRR (dB)
100k
1M
FIGURE 8. EL8172 CMRR vs FREQUENCY
60
PSRR40
PSRR+
60
PSRR40
AV = 10
AV = 10
20
20
0
10
100
1k
10k
100k
0
10
1M
100
FREQUENCY (Hz)
10k
100k
1M
FIGURE 10. EL8172 PSRR vs FREQUENCY
1400
INPUT VOLTAGE NOISE (nV/√Hz)
700
1200
1000
800
600
AV = 10
400
200
0
1k
FREQUENCY (Hz)
FIGURE 9. EL8171 PSRR vs FREQUENCY
INPUT VOLTAGE NOISE (nV/√Hz)
10k
FREQUENCY (Hz)
FREQUENCY (Hz)
FIGURE 7. EL8171 CMRR vs FREQUENCY
80
1k
1
10
100
1k
10k
100k
FREQUENCY (Hz)
FIGURE 11. EL8171 VOLTAGE NOISE SPECTRAL DENSITY
5
600
500
400
300
AV = 100
200
100
0
1
10
100
1k
10k
100k
FREQUENCY (Hz)
FIGURE 12. EL8172 VOLTAGE NOISE SPECTRAL DENSITY
FN6293.5
July 27, 2009
EL8171, EL8172
Typical Performance Curves V+ = 5V, V- = 0V,VCM = 2.5V, RL = Open, unless otherwise specified. (Continued)
2.0
6
1.8
4
3
2
1.6
CURRENT NOISE (pA/√Hz)
CURRENT NOISE (pA/√Hz)
5
AV = 10
1
1.4
1.2
1.0
0.8
AV = 100
0.6
0.4
0.2
0
0.0
1
10
100
1k
10k
100k
1
10
100
FREQUENCY (Hz)
100k
FIGURE 14. EL8172 CURRENT NOISE SPECTRAL DENSITY
VOLTAGE NOISE (5µV/DIV)
VOLTAGE NOISE (2µV/DIV)
FIGURE 13. EL8171 CURRENT NOISE SPECTRAL DENSITY
TIME (1s/DIV)
TIME (1s/DIV)
FIGURE 15. EL8171 0.1Hz TO 10Hz INPUT VOLTAGE NOISE
(GAIN = 10)
FIGURE 16. EL8172 0.1Hz TO 10Hz INPUT VOLTAGE NOISE
(GAIN = 100)
80
90
N = 1000
75
70
65
MEDIAN
60
55
MIN
50
45
40
-40
N = 1500
85
MAX
SUPPLY CURRENT (μA)
SUPPLY CURRENT (μA)
10k
1k
FREQUENCY (Hz)
80
MAX
75
70
MEDIAN
65
60
MIN
55
50
45
-20
0
20
40
60
80
100
120
TEMPERATURE (°C)
FIGURE 17. EL8171 SUPPLY CURRENT vs TEMPERATURE,
V+, V- = ±2.5V, VIN = 0V
6
40
-40
-20
0
20
40
60
80
100
120
TEMPERATURE (°C)
FIGURE 18. EL8172 SUPPLY CURRENT vs TEMPERATURE,
V+, V- = ±2.5V, VIN = 0V
FN6293.5
July 27, 2009
EL8171, EL8172
Typical Performance Curves V+ = 5V, V- = 0V,VCM = 2.5V, RL = Open, unless otherwise specified. (Continued)
2.5
0.7
N = 1500
N = 1000
2.0
0.5
1.5
MAX
MAX
0.3
0.5
VOS (µV)
VOS (µV)
1.0
MEDIAN
0
-0.5
0.1
MEDIAN
-0.1
-0.3
-1.0
MIN
-0.5
-1.5
MIN
-2.0
-40
-20
0
20
40
60
80
100
-0.7
120
-40
-20
0
TEMPERATURE (°C)
FIGURE 19. EL8171 VOS vs TEMPERATURE, V+, V- = ±2.5V,
VIN = 0V
60
80
100
120
0.9
N = 1000
2.0
N = 1500
0.7
1.5
MAX
0.5
VOS (µV)
1.0
VOS (µV)
40
FIGURE 20. EL8172 VOS vs TEMPERATURE, V+, V- = ±2.5V,
VIN = 0V
2.5
0.5
MEDIAN
0
-0.5
-1.0
MAX
0.3
0.1
MEDIAN
-0.1
-0.3
-1.5
MIN
MIN
-0.5
-2.0
-2.5
-0.7
-40
-20
0
20
40
60
80
100
120
-40
-20
0
TEMPERATURE (°C)
40
60
80
100
120
FIGURE 22. EL8172 VOS vs TEMPERATURE, V+, V- = ±1.2V,
VIN = 0V
140
140
N = 1500
N = 1000
MAX
130
CMRR (dB)
110
MEDIAN
100
MAX
130
120
120
110
MEDIAN
100
90
90
MIN
MIN
80
-40
20
TEMPERATURE (°C)
FIGURE 21. EL8171 VOS vs TEMPERATURE, V+, V- = ±1.2V,
VIN = 0V
CMRR (dB)
20
TEMPERATURE (°C)
-20
0
20
40
60
80
100
TEMPERATURE (°C)
FIGURE 23. EL8171 CMRR vs TEMPERATURE,
VCM = +2.5V TO -2.5V, V+, V- = ±2.5V
7
120
80
-40
-20
0
20
40
60
80
100
120
TEMPERATURE (°C)
FIGURE 24. EL8172 CMRR vs TEMPERATURE,
VCM = +2.5V TO -2.5V, V+, V- = ±2.5V
FN6293.5
July 27, 2009
EL8171, EL8172
Typical Performance Curves V+ = 5V, V- = 0V,VCM = 2.5V, RL = Open, unless otherwise specified. (Continued)
140
140
MAX
130
130
120
120
110
110
PSRR (dB)
PSRR (dB)
N = 1000
100
MEDIAN
90
80
N = 1500
MAX
MEDIAN
100
90
MIN
80
MIN
70
60
70
-40
-20
0
20
40
60
80
100
60
120
-40
-20
0
20
FIGURE 25. EL8171 PSRR vs TEMPERATURE,
V+, V- = ±1.2V TO ±2.5V
0.7
80
100
120
100
120
1.5
N = 1000
N = 1500
1.3
0.5
GAIN ERROR (%)
GAIN ERROR (%)
60
FIGURE 26. EL8172 PSRR vs TEMPERATURE,
V+, V- = ±1.2V TO ±2.5V
0.6
MAX
0.4
0.3
0.2
MEDIAN
0.1
0
-0.1
-40
40
TEMPERATURE (°C)
TEMPERATURE (°C)
0
MAX
0.9
0.7
0.5
0.3
MEDIAN
0.1
MIN
-20
1.1
20
40
60
80
TEMPERATURE (°C)
100
-0.1
-40
120
MIN
-20
0
20
40
60
80
TEMPERATURE (°C)
FIGURE 27. EL8171% GAIN ERROR vs TEMPERATURE,
RL = 100k
FIGURE 28. EL8172% GAIN ERROR vs TEMPERATURE,
RL = 100k
4.91
4.91
N = 1000
N = 1500
4.90
4.90
4.89
4.89
4.88
VOUT (V)
VOUT (V)
MAX
4.87
4.86
MEDIAN
MAX
4.87
4.86
MEDIAN
4.85
4.85
MIN
MIN
4.84
4.84
4.83
-40
4.88
-20
0
20
40
60
80
TEMPERATURE (°C)
100
FIGURE 29. EL8171 VOUT HIGH vs TEMPERATURE,
RL = 1k, V+, V- = ±2.5V
8
120
4.83
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
100
120
FIGURE 30. EL8172 VOUT HIGH vs TEMPERATURE,
RL = 1k, V+, V- = ±2.5V
FN6293.5
July 27, 2009
EL8171, EL8172
Typical Performance Curves V+ = 5V, V- = 0V,VCM = 2.5V, RL = Open, unless otherwise specified. (Continued)
180
200
N = 1000
180
160
VOUT (mV)
VOUT (mV)
MAX
160
MEDIAN
140
MAX
150
140
MEDIAN
130
MIN
120
120
MIN
110
100
80
-40
N = 1000
170
100
-20
0
20
40
60
80
100
90
-40
120
-20
0
TEMPERATURE (°C)
0.65
0.60
MAX
0.58
N = 1000
+SLEW RATE (V/µs)
+SLEW RATE (V/µs)
0.60
MEDIAN
0.50
0.45
MIN
0.40
100
120
FIGURE 32. EL8172 VOUT LOW vs TEMPERATURE,
RL = 1k, V+, V- = ±2.5V
FIGURE 31. EL8171 VOUT LOW vs TEMPERATURE,
RL = 1k, V+, V- = ±2.5V
0.55
20
40
60
80
TEMPERATURE (°C)
MAX
N = 1500
0.56
0.54
0.52
MEDIAN
0.50
0.48
0.46
MIN
0.44
0.35
0.30
-40
0.42
-20
0
20
40
60
80
TEMPERATURE (°C)
100
FIGURE 33. EL8171 +SLEW RATE vs TEMPERATURE,
INPUT = ±0.015V @ GAIN + 100
0.70
0.40
-40
120
-20
0
20
40
60
80
TEMPERATURE (°C)
100
120
FIGURE 34. EL8172 +SLEW RATE vs TEMPERATURE,
INPUT = ±0.015V @ GAIN + 100
0.65
N = 1000
MAX
N = 1500
0.65
MAX
0.60
-SLEW RATE (V/µS)
- SLEW RATE (V/µS)
0.60
MEDIAN
0.55
0.50
0.45
MIN
0.40
0.55
MEDIAN
0.50
0.45
MIN
0.35
0.30
-40
-20
0
20
40
60
80
100
TEMPERATURE (°C)
FIGURE 35. EL8171 -SLEW RATE vs TEMPERATURE,
INPUT = ±0.015V @ GAIN + 100
9
120
0.40
-40
-20
0
20
40
60
80
100
120
TEMPERATURE (°C)
FIGURE 36. EL8172 -SLEW RATE vs TEMPERATURE,
INPUT = ±0.015V @ GAIN + 100
FN6293.5
July 27, 2009
EL8171, EL8172
Pin Descriptions
EL8171/EL8172
PIN NAME
EQUIVALENT CIRCUIT
PIN FUNCTION
1
DNC
2
IN-
Circuit 1A, Circuit 1B
3
IN+
Circuit 1A, Circuit 1B
4
V-
Circuit 3
5
FB-
Circuit 1A, Circuit 1B
8
FB+
Circuit 1A, Circuit 1B
7
V+
Circuit 3
Positive supply terminal.
6
VOUT
Circuit 2
Output Voltage.
Do Not Connect; Internal connection - Must be left floating.
High impedance input terminals. EL8172 input circuit is shown in Circuit 1A, and
the EL8171 input circuit is shown in Circuit 1B. EL8171: to avoid offset drift, it is
recommended that the terminals are not overdriven beyond 1V and the input
current must never exceed 5mA.
Negative supply terminal.
High impedance feedback terminals. EL8172 input circuit is shown in Circuit 1A,
and the EL8171 input circuit is shown in Circuit 1B. EL8171: to avoid offset drift, it
is recommended that the terminals are not overdriven beyond 1V and the input
current must never exceed 5mA.
V+
V+
IN+
FB+
INFB-
INFB-
V-
V+
IN+
FB+
OUT
V-
V-
V+
CAPACITIVELY
COUPLED
ESD CLAMP
V-
CIRCUIT 1A
CIRCUIT 1B
Description of Operation and Application
Information
Product Description
The EL8171 and EL8172 are micropower instrumentation
amplifiers (in-amps) which deliver rail-to-rail input amplification
and rail-to-rail output swing on a single 2.4V to 5.5V supply. The
EL8171 and EL8172 also deliver excellent DC and AC
specifications while consuming only 65µA typical supply
current. Because EL8171 and EL8172 provide an independent
pair of feedback terminals to set the gain and to adjust the
output level, these in-amps achieve high common-mode
rejection ratio regardless of the tolerance of the gain setting
resistors. The EL8171 is internally compensated for a minimum
closed loop gain of 10 or greater, well suited for moderate to
high gains. For higher gains, the EL8172 is internally
compensated for a minimum gain of 100.
Input Protection
All input and feedback terminals of the EL8171 and EL8172
have internal ESD protection diodes to both positive and
negative supply rails, limiting the input voltage to within one
diode drop beyond the supply rails. The inverting inputs and
FB- inputs have ESD diodes to the V-rail, and the non-inverting
inputs and FB+ terminals have ESD diodes to the V+ rail. The
EL8172 has additional back-to-back diodes across the input
terminals and also across the feedback terminals. If overdriving
the inputs is necessary, the external input current must never
exceed 5mA. On the other hand, the EL8171 has no clamps to
limit the differential voltage on the input terminals allowing
10
CIRCUIT 2
CIRCUIT 3
higher differential input voltages at lower gain applications. It is
recommended however, that the input terminals of the EL8171
are not overdriven beyond 1V to avoid offset drift. An external
series resistor may be used as an external protection to limit
excessive external voltage and current from damaging the
inputs.
Input Stage and Input Voltage Range
The input terminals (IN+ and IN-) of the EL8171 and EL8172
are single differential pair P-MOSFET devices aided by an
Input Range Enhancement Circuit (IREC) to increase the
headroom of operation of the common-mode input voltage.
The feedback terminals (FB+ and FB-) also have a similar
topology. As a result, the input common-mode voltage range
of both the EL8171 and EL8172 is rail-to-rail. These in-amps
are able to handle input voltages that are at or slightly
beyond the supply and ground making these in-amps well
suited for single 5V or 3.3V low voltage supply systems.
There is no need to move the common-mode input of the inamps to achieve symmetrical input voltage.
Output Stage and Output Voltage Range
A pair of complementary MOSFET devices drive the output
VOUT to within a few mV of the supply rails. At a 100kΩ load,
the PMOS sources current and pulls the output up to 4mV
below the positive supply, while the NMOS sinks current and
pulls the output down to 4mV above the negative supply, or
ground in the case of a single supply operation. The current
sinking and sourcing capability of the EL8171 and EL8172
are internally limited to less than 35mA.
FN6293.5
July 27, 2009
EL8171, EL8172
Gain Setting
2.4V TO 5.5V
VIN, the potential difference across IN+ and IN-, is replicated
(less the input offset voltage) across FB+ and FB-. The
obsession of the EL8171 and EL8172 in-amp is to maintain
the differential voltage across FB+ and FB- equal to IN+ and
IN-; (FB+ - FB-) = (IN+ - IN-). Consequently, the transfer
function can be derived. The gain of the EL8171 and EL8172
is set by two external resistors, the feedback resistor RF, and
the gain resistor RG.
2.4V TO 5.5V
7
2 INVIN/2
8 FB+
VCM
5 FB-
1
2 IN-
-
VIN/2
8 FB+
VCM
V+
+
5 FB-
2.4V TO 5.5V
EL8171/2
-
V-
RG
RF
V+
+
EL8171/2
6
VOUT
+
-
FIGURE 38. CIRCUIT 2 - GAIN SETTING AND REFERENCE
CONNECTION
RF ⎞
RF ⎞
⎛
⎛
V OUT = ⎜ 1 + --------⎟ ( V IN ) + ⎜ 1 + --------⎟ ( V REF )
R G⎠
R G⎠
⎝
⎝
V-
(EQ. 2)
susceptibility to external noise is reduced, however the VREF
source must be capable of sourcing or sinking the feedback
current from VOUT through RF and RG.
2.4V TO 5.5V
FIGURE 37. CIRCUIT 1 - GAIN IS BY EXTERNAL RESISTORS
RF AND RG
7
1
VIN/2
3 IN+
(EQ. 1)
2 INVIN/2
In Figure 37, the FB+ pin and one end of resistor RG are
connected to GND. With this configuration, Equation 1 is
only true for a positive swing in VIN; negative input swings
will be ignored and the output will be at ground.
8 FB+
VCM
Unlike a three-op amp instrumentation amplifier, a finite
series resistance seen at the REF terminal does not degrade
the EL8171 and EL8172's high CMRR performance,
eliminating the need for an additional external buffer
amplifier. Circuit 2 (Figure 38) uses the FB+ pin to provide a
high impedance REF terminal.
The FB+ pin is used as a REF terminal to center or to adjust
the output. Because the FB+ pin is a high impedance input,
an economical resistor divider can be used to set the voltage
at the REF terminal without degrading or affecting the CMRR
performance. Any voltage applied to the REF terminal will
shift VOUT by VREF times the closed loop gain, which is set
by resistors RF and RG. See Circuit 2 (Figure 38). Note that
any noise or unwanted signals on the reference supply will
be amplified at the output according to Equation 2.
The FB+ pin can also be connected to the other end of resistor,
RG. See Circuit 3 (Figure 39). Keeping the basic concept that
the EL8171 and EL8172 in-amps maintain constant differential
voltage across the input terminals and feedback terminals (IN+
- IN- = FB+ - FB-), the transfer function of Circuit 3 can be
derived. Note that the VREF gain term is eliminated and
5 FB-
V+
+
EL8171/2
6
VOUT
+
-
V4
Reference Connection
11
VOUT
4
R1
R2
RF
RF ⎞
⎛
V OUT = ⎜ 1 + --------⎟ V IN
R
⎝
G⎠
6
+
REF
4
RG
3 IN+
1
VIN/2
3 IN+
7
VIN/2
RG
RF
VREF
FIGURE 39. CIRCUIT 3 - REFERENCE CONNECTION WITH AN
AVAILABLE VREF
RF ⎞
⎛
V OUT = ⎜ 1 + --------⎟ ( V IN ) + ( V REF )
R
⎝
G⎠
(EQ. 3)
External Resistor Mismatches
Because of the independent pair of feedback terminals
provided by the EL8171 and EL8172, the CMRR is not
degraded by any resistor mismatches. Hence, unlike a three op
amp and especially a two op amp in-amp, the EL8171 and
EL8172 reduce the cost of external components by allowing the
use of 1% or more tolerance resistors without sacrificing CMRR
performance. The EL8171 and EL8172 CMRR will be
maintained regardless of the tolerance of the resistors used.
Gain Error and Accuracy
The EL8172 has a Gain Error (EG) of 0.2% typical. The
EL8171 has an EG of 0.15% typical. The gain error indicated
in the “Electrical Specifications” table on page 2 is the inherent
gain error of the EL8171 and EL8172 and does not include
FN6293.5
July 27, 2009
EL8171, EL8172
the gain error contributed by the resistors. There is an
additional gain error due to the tolerance of the resistors used.
The resulting non-ideal transfer function effectively becomes:
where:
RF ⎞
⎛
V OUT = ⎜ 1 + --------⎟ × [ 1 – ( E RG + E RF + E G ) ] × V IN
R G⎠
⎝
• PDMAX for each amplifier can be calculated as shown in
Equation 7:
(EQ. 4)
• PDMAXTOTAL is the sum of the maximum power
dissipation of each amplifier in the package (PDMAX)
V OUTMAX
PD MAX = 2*V S × I SMAX + ( V S - V OUTMAX ) × ---------------------------RL
(EQ. 7)
Where:
ERG = Tolerance of RG
ERF = Tolerance of RF
where:
EG
• TMAX = Maximum ambient temperature
= Gain Error of the EL8171 or EL8172
• θJA = Thermal resistance of the package
The term [1-(ERG +ERF +EG)] is the deviation from the
theoretical gain. Thus, (ERG +ERF +EG) is the total gain
error. For example, if 1% resistors are used for the EL8171,
the total gain error would be:
• PDMAX = Maximum power dissipation of 1 amplifier
= ± ( E RG + E RF + E G ( typical ) )
• IMAX = Maximum supply current of 1 amplifier
= ± ( 0.01 + 0.01 + 0.003 )
(EQ. 5)
= ± 2.3%
• VS = Supply voltage (Magnitude of V+ and V-)
• VOUTMAX = Maximum output voltage swing of the
application
• RL = Load resistance
Power Dissipation
It is possible to exceed the +150°C maximum junction
temperatures under certain load and power-supply
conditions. It is therefore important to calculate the
maximum junction temperature (TJMAX) for all applications
to determine if power supply voltages, load conditions, or
package type need to be modified to remain in the safe
operating area. These parameters are related in Equation 6:
T JMAX = T MAX + ( θ JA xPD MAXTOTAL )
(EQ. 6)
All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems.
Intersil Corporation’s quality certifications can be viewed at www.intersil.com/design/quality
Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without
notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and
reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result
from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries.
For information regarding Intersil Corporation and its products, see www.intersil.com
12
FN6293.5
July 27, 2009
EL8171, EL8172
Small Outline Package Family (SO)
A
D
h X 45°
(N/2)+1
N
A
PIN #1
I.D. MARK
E1
E
c
SEE DETAIL “X”
1
(N/2)
B
L1
0.010 M C A B
e
H
C
A2
GAUGE
PLANE
SEATING
PLANE
A1
0.004 C
0.010 M C A B
L
b
0.010
4° ±4°
DETAIL X
MDP0027
SMALL OUTLINE PACKAGE FAMILY (SO)
INCHES
SYMBOL
SO-14
SO16 (0.300”)
(SOL-16)
SO20
(SOL-20)
SO24
(SOL-24)
SO28
(SOL-28)
TOLERANCE
NOTES
A
0.068
0.068
0.068
0.104
0.104
0.104
0.104
MAX
-
A1
0.006
0.006
0.006
0.007
0.007
0.007
0.007
±0.003
-
A2
0.057
0.057
0.057
0.092
0.092
0.092
0.092
±0.002
-
b
0.017
0.017
0.017
0.017
0.017
0.017
0.017
±0.003
-
c
0.009
0.009
0.009
0.011
0.011
0.011
0.011
±0.001
-
D
0.193
0.341
0.390
0.406
0.504
0.606
0.704
±0.004
1, 3
E
0.236
0.236
0.236
0.406
0.406
0.406
0.406
±0.008
-
E1
0.154
0.154
0.154
0.295
0.295
0.295
0.295
±0.004
2, 3
e
0.050
0.050
0.050
0.050
0.050
0.050
0.050
Basic
-
L
0.025
0.025
0.025
0.030
0.030
0.030
0.030
±0.009
-
L1
0.041
0.041
0.041
0.056
0.056
0.056
0.056
Basic
-
h
0.013
0.013
0.013
0.020
0.020
0.020
0.020
Reference
-
16
20
24
28
Reference
-
N
SO-8
SO16
(0.150”)
8
14
16
Rev. M 2/07
NOTES:
1. Plastic or metal protrusions of 0.006” maximum per side are not included.
2. Plastic interlead protrusions of 0.010” maximum per side are not included.
3. Dimensions “D” and “E1” are measured at Datum Plane “H”.
4. Dimensioning and tolerancing per ASME Y14.5M-1994
13
FN6293.5
July 27, 2009