NOT RECOMMENDED FOR NEW DESIGNS
NO RECOMMENDED REPLACEMENT
contact our Technical Support Center at
1-888-INTERSIL or www.intersil.com/tsc
ISL28271, ISL28272
DATASHEET
Rev X.00
Dual Micropower, Single Supply, Rail-to-Rail Input and Output (RRIO)
Instrumentation Amplifier
The ISL28271 and ISL28272 are dual micropower
instrumentation amplifiers (in-amps) optimized for single
supply operation over the +2.4V to +5.5V range.
Both devices feature an Input Range Enhancement Circuit
(IREC) which maintains CMRR performance for input
voltages equal to the positive and negative supply rails. The
input signal is capable of swinging 10% above the positive
supply rail and to 100mV below the negative supply with only
a slight degradation of the CMRR performance. The output
operation is rail-to-rail.
The ISL28271 is compensated for a minimum gain of 10 or
more. For higher gain applications, the ISL28272 is
compensated for a minimum gain of 100. The in-amps have
CMOS input devices for maximum input common voltage
range. The amplifiers can be operated from one lithium cell
or two Ni-Cd batteries.
Ordering Information
PART NUMBER
(Note)
PART
MARKING
Features
• 120µA typical supply current for both channels
• 30pA max input bias current
• 100dB CMRR, PSRR
• 0.7µV/°C offset voltage temperature coefficient
• 180kHz 3dB Bandwidth - ISL28271
• 100kHz 3dB Bandwidth - ISL28272
• 0.5V/µs slew rate
• Single supply operation
• Rail-to-rail input and output (RRIO)
• Input is capable of swinging above V+ and below V(ground sensing)
• 0.081%1 typical gain error - ISL28271
• -0.19%1 typical gain error - ISL28272
PACKAGE
(Pb-free)
PKG. DWG. #
• Pb-free available (RoHS compliant)
ISL28271FAZ*
28271 FAZ
16 Ld QSOP MDP0040
Applications
ISL28272FAZ*
28272 FAZ
16 Ld QSOP MDP0040
• Battery- or solar-powered systems
ISL28271INEVAL1Z
Evaluation Platform
• Strain gauge
ISL28272INEVAL1Z
Evaluation Platform
• Sensor signal conditioning
*Add “-T7” suffix for tape and reel. Please refer to TB347 for details
on reel specifications.
• Medical devices
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.
• Industrial instrumentations
Related Literature
• AN1290, ISL2827xINEVAL1Z Evaluation Board User’s
Guide
• AN1298, Instrumentation Amplifier Application Note
Pinout
ISL28271, ISL28272
(16 LD QSOP)
TOP VIEW
16 V+
NC 1
15 OUT_B
OUT_A 2
FB+_A 3
- +
14 FB+_B
13 FB-_B
IN-_A 5
12 IN-_B
IN+_A 6
11 IN+_B
EN_A 7
10 EN_B
V- 8
Rev X.00
+ -
FB-_A 4
9
NC
Page 1 of 14
ISL28271, ISL28272
Absolute Maximum Ratings (TA = +25°C)
Thermal Information
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5V
Supply Turn-on Voltage Slew Rate . . . . . . . . . . . . . . . . . . . . . 1V/µs
Input Current (IN, FB) ISL28272 . . . . . . . . . . . . . . . . . . . . . . . . 5mA
Differential Input Voltage (IN, FB) ISL28272 . . . . . . . . . . . . . . . 0.5V
Input Current (IN, FB) ISL28271 . . . . . . . . . . . . . . . . . . . . . . . . 5mA
Differential Input (IN, FB) Voltage ISL28271 . . . . . . . . . . . . . . . 1.0V
Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . V- - 0.5V to V+ + 0.5V
ESD Rating
Human Body Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3kV
Machine Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .300V
Thermal Resistance
JA (°C/W)
16 Ld QSOP Package . . . . . . . . . . . . . . . . . . . . . . .
112
Output Short-Circuit Duration . . . . . . . . . . . . . . . . . . . . . . .Indefinite
Ambient Operating Temperature Range . . . . . . . . .-40°C to +125°C
Storage Temperature Range . . . . . . . . . . . . . . . . . .-65°C to +150°C
Operating Junction Temperature . . . . . . . . . . . . . . . . . . . . . +125°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
VOS
TCVOS
V+ = +5V, V- = GND, VFB+ = 1/2V+, RL = Open, TA = +25°C, unless otherwise specified. Boldface limits apply
over the operating temperature range, -40°C to +125°C.
DESCRIPTION
Input Offset Voltage
CONDITIONS
MIN
(Note 1)
TYP
MAX
(Note 1)
UNIT
ISL28271
-600
-1200
±35
600
1200
µV
ISL28272
-500
-750
±35
500
750
µV
Input Offset Voltage Temperature
Coefficient -40°C to +125°C
0.7
µV/°C
IOS
Input Offset Current between IN+ and
IN-, and between FB+ and FB-
See graphs for extended temperature range
-40°C to +85°C
-30
-80
±5
30
80
pA
IB
Input Bias Current (IN+, IN-, FB+, and
FB- terminals)
See graphs for extended temperature range
-40°C to +85°C
-30
-80
±10
30
80
pA
eN
Input Noise Voltage
ISL28271
f = 0.1Hz to 10Hz
ISL28272
Input Noise Voltage Density
ISL28271
fo = 1kHz
ISL28272
iN
Input Noise Current Density
ISL28271
fo = 1kHz
ISL28272
RIN
Input Resistance
VIN
Input Voltage Range
V+ = 2.4V to 5.0V
Common Mode Rejection Ratio
ISL28271
CMRR
PSRR
EG
µVP-P
6
µVP-P
240
nV/Hz
78
nV/Hz
0.92
pA/Hz
0.2
pA/Hz
1
G
0
VCM = 0V to 5V
V+
V
80
70
100
dB
ISL28272
80
75
100
dB
Power Supply Rejection Ratio
V+ = 2.4V to 5V
80
75
100
dB
Gain Error
ISL28271
+0.081
%
ISL28272
Rev X.00
10
RL = 100k to 2.5V
-0.19
Page 2 of 14
ISL28271, ISL28272
Electrical Specifications
PARAMETER
VOUT
V+ = +5V, V- = GND, VFB+ = 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
Maximum Voltage Swing
CONDITIONS
MIN
(Note 1)
Output low, RL = 100k
Output low, RL = 1k
SR
-3db BW
TYP
MAX
(Note 1)
UNIT
3
6
30
mV
130
175
225
mV
Output high, RL = 100k
4.980
4.980
4.99
V
Output high, RL = 1k
4.85
4.80
4.88
V
Slew Rate
RL = 1k to GND
0.4
0.35
0.5
-3dB Bandwidth
RL = 10k
0.7
0.75
V/µs
ISL28271
180
kHz
ISL28272
100
kHz
IS,EN
Supply Current, Enabled
Both A and B channels enabled, EN = V-
120
156
200
µA
IS,DIS
Supply Current, Disabled
Both A and B channels disabled, EN = V+
4
7
9
µA
VINH
EN Enable Pin High Level
VINL
EN Enable Pin Low Level
IENH
EN Input Current High
EN = V+
IENL
EN Input Current Low
EN = V-
Supply Operating Range
V+ to V- (Note 2)
2.4
ISC+
Short Circuit Output Current
V+ = 5V, RL = 10
28
25
31
mA
ISC-
Short Circuit Output Current
V+ = 5V, RL = 10
24
20
26
mA
VSUPPLY
2
V
0.8
V
0.8
1
1.3
µA
26
50
100
nA
5.5
V
NOTE:
1. Parts are 100% tested at +25°C. Over temperature limits established by characterization and are not production tested.
2. VSUPPLY = +5.25V max when VENL = +V (device in disable state).
Rev X.00
Page 3 of 14
ISL28271, ISL28272
Typical Performance Curves
70
GAIN = 500
GAIN (dB)
GAIN (dB)
GAIN = 100
40
GAIN = 50
30
GAIN = 10,000
80
GAIN = 200
50
GAIN = 20
GAIN = 5,000
70
GAIN = 1,000
60
GAIN = 500
50
GAIN = 200
GAIN = 100
40
1
10
100
1k
10k
100k
30
1M
1
10
FREQUENCY (Hz)
FIGURE 1. ISL28271 FREQUENCY RESPONSE vs CLOSED
LOOP GAIN, V+ = VCM = 5V
70
GAIN = 500
GAIN = 200
GAIN = 100
40
GAIN = 50
30
10
100
GAIN = 5,000
70
10k
100k
GAIN = 200
GAIN = 100
1
10
FREQUENCY (Hz)
70
GAIN = 1000
60
GAIN = 500
GAIN = 50
GAIN = 10
1
10
100
1k
10k
FREQUENCY (Hz)
100k
1M
100k
1M
GAIN = 1,000
60
30
VCM = +10mV
VOUT = 10mVP-P
RL = 10k
GAIN = 2,000
GAIN = 500
GAIN = 200
GAIN = 100
40
FIGURE 5. ISL28271 FREQUENCY RESPONSE vs CLOSED
LOOP GAIN, V+ = 5V, VCM = 10mV
Rev X.00
GAIN = 5,000
70
50
GAIN = 20
20
GAIN = 10,000
80
GAIN = 100
30
10
90
VCM = +10mV
VOUT = 10mVP-P
RL = 10k
GAIN = 200
40
100
1k
10k
FREQUENCY (Hz)
FIGURE 4. ISL28272 FREQUENCY RESPONSE vs CLOSED
LOOP GAIN, VCM = 1/2V+
GAIN (dB)
GAIN (dB)
50
VCM = 2.5V
VOUT = 10mVP-P
RL = 10k
GAIN = 500
30
1M
FIGURE 3. ISL28271 FREQUENCY RESPONSE vs CLOSED
LOOP GAIN, V+ = 5V, VCM = 1/2V+
1M
GAIN = 1,000
60
40
1k
100k
GAIN = 2,000
50
GAIN = 10
1
GAIN = 10,000
80
GAIN = 20
20
10
90
GAIN (dB)
GAIN (dB)
50
100
1k
10k
FREQUENCY (Hz)
FIGURE 2. ISL28272 FREQUENCY RESPONSE vs CLOSED
LOOP GAIN, VCM = V+
VCM = 2.5V
VOUT = 10mVP-P
RL = 10k
GAIN = 1000
60
VCM = 5V
VOUT = 10mVP-P
RL = 10k
GAIN = 2,000
GAIN = 10
20
10
90
VCM = 5V
VOUT = 10mVP-P
RL = 10k
GAIN = 1000
60
V+ = +5V, V- = GND, VFB+ = 1/2V+, RL = Open, TA = +25°C, unless otherwise specified.
1
10
100
1k
10k
FREQUENCY (Hz)
100k
1M
FIGURE 6. ISL28272 FREQUENCY RESPONSE vs CLOSED
LOOP GAIN, VCM = V-
Page 4 of 14
ISL28271, ISL28272
Typical Performance Curves
V+ = +5V, V- = GND, VFB+ = 1/2V+, RL = Open, TA = +25°C, unless otherwise specified.
45
25
30
V+ = 2.4V
15
10
AV = 10
RL = 10k
CL = 10pF
5
RF/RG = 10
RF = 1k
RG = 100
0
10
100
V+ = 5V
35
GAIN (dB)
GAIN (dB)
40
V+ = 5V
20
V+ = 2.4V
25
20
AV = 100
RL = 10k
CL = 10pF
RF/RG = 100
RF = 10k
RG = 100
15
10
5
1k
10k
100k
0
1M
10
100
1k
10k
100k
1M
FREQUENCY (Hz)
FREQUENCY (Hz)
FIGURE 7. ISL28271 FREQUENCY RESPONSE vs SUPPLY
VOLTAGE
25
FIGURE 8. ISL28272 FREQUENCY RESPONSE vs SUPPLY
VOLTAGE
50
470pF
820pF
2200pF
45
20
15
AV = 10
R = 10k
CL = 10pF
RF/RG = 10
RF = 1k
RG = 100
10
5
10
100
40
GAIN (dB)
GAIN (dB)
1200pF
220pF
100pF
820pF
35
AV = 100
R = 10k
CL = 10pF
RF/RG = 100
RF = 10k
RG = 100
30
1k
10k
100k
25
1M
10
100
56pF
1k
10k
100k
1M
FREQUENCY (Hz)
FREQUENCY (Hz)
FIGURE 9. ISL28271 FREQUENCY RESPONSE vs CLOAD
FIGURE 10. ISL28272 FREQUENCY RESPONSE vs CLOAD
90
120
80
100
70
CMRR (dB)
CMRR (dB)
60
50
40
AV = 10
30
20
10
80
60
AV = 100
40
20
0
-10
10
100
1k
10k
100k
FREQUENCY (Hz)
FIGURE 11. ISL28271 CMRR vs FREQUENCY
Rev X.00
1M
0
10
100
1k
10k
100k
1M
FREQUENCY (Hz)
FIGURE 12. ISL28272 CMRR vs FREQUENCY
Page 5 of 14
ISL28271, ISL28272
Typical Performance Curves
120
120
100
100
80
80
PSRR+
PSRR (dB)
PSRR (dB)
V+ = +5V, V- = GND, VFB+ = 1/2V+, RL = Open, TA = +25°C, unless otherwise specified.
60
PSRR40
AV = 10
PSRR+
60
PSRR-
40
AV = 100
20
20
0
10
100
1k
10k
100k
0
10
1M
100
FREQUENCY (Hz)
100k
1M
FIGURE 14. ISL28272 PSRR vs FREQUENCY
700
INPUT VOLTAGE NOISE (nV/Hz)
1400
INPUT VOLTAGE NOISE (nV/Hz)
10k
FREQUENCY (Hz)
FIGURE 13. ISL28271 PSRR vs FREQUENCY
1200
1000
800
600
AV = 10
400
200
0
1
1k
10
100
1k
10k
600
500
400
300
100
0
100k
AV = 100
200
1
10
FREQUENCY (Hz)
100
1k
10k
100k
FREQUENCY (Hz)
FIGURE 15. ISL28271 INPUT VOLTAGE NOISE SPECTRAL
DENSITY
FIGURE 16. ISL28272 INPUT VOLTAGE NOISE SPECTRAL
DENSITY
2.0
6
CURRENT NOISE (pA/Hz)
CURRENT NOISE (pA/Hz)
1.8
5
4
3
2
AV = 10
1
0
1
10
100
1k
10k
100k
FREQUENCY (Hz)
FIGURE 17. ISL28271 INPUT CURRENT NOISE SPECTRAL
DENSITY
Rev X.00
1.6
1.4
1.2
1.0
0.8
0.6
AV = 100
0.4
0.2
0.0
1
10
100
1k
10k
100k
FREQUENCY (Hz)
FIGURE 18. ISL28272 INPUT CURRENT NOISE SPECTRAL
DENSITY
Page 6 of 14
ISL28271, ISL28272
V+ = +5V, V- = GND, VFB+ = 1/2V+, RL = Open, TA = +25°C, unless otherwise specified.
VOLTAGE NOISE (5µV/DIV)
VOLTAGE NOISE (2µV/DIV)
Typical Performance Curves
TIME (1s/DIV)
TIME (1s/DIV)
FIGURE 19. ISL28271 0.1Hz TO 10Hz INPUT VOLTAGE NOISE,
GAIN = 10
FIGURE 20. ISL28272 0.1Hz TO 10Hz INPUT VOLTAGE NOISE,
GAIN = 100
160
n = 3000
MAX
170
150
MEDIAN
130
MAX
150
SUPPLY CURRENT (µA)
SUPPLY CURRENT (µA)
190 n = 3000
110
MIN
90
140
130
MEDIAN
120
110
MIN
100
70
50
-40
-20
0
20
40
60
80
100
90
-40
120
-20
0
5.0
100
120
6
4.0
SUPPLY CURRENT (µA)
SUPPLY CURRENT (µA)
80
n = 3000
MAX
4.5
MEDIAN
3.5
3.0
MIN
0
20
40
60
80
MAX
5
4
3
MIN
MEDIAN
2
1
100
120
TEMPERATURE (°C)
FIGURE 23. ISL28271 SUPPLY CURRENT DISABLED vs
TEMPERATURE, V+, V- = ±2.5V, VIN = 0V
Rev X.00
60
7
n = 3000
-20
40
FIGURE 22. ISL28272 SUPPLY CURRENT ENABLED vs
TEMPERATURE, V+, V- = ±2.5V, VIN = 0V
FIGURE 21. ISL28271 SUPPLY CURRENT ENABLED vs
TEMPERATURE, V+, V- = ±2.5V, VIN = 0V
2.5
-40
20
TEMPERATURE (°C)
TEMPERATURE (°C)
0
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
100
120
FIGURE 24. ISL28272 SUPPLY CURRENT DISABLED vs
TEMPERATURE, V+, V- = ±2.5V, VIN = 0V
Page 7 of 14
ISL28271, ISL28272
Typical Performance Curves
160
V+ = +5V, V- = GND, VFB+ = 1/2V+, RL = Open, TA = +25°C, unless otherwise specified.
190
n = 3000
150
170
MAX
MAX
130
CMRR (dB)
CMRR (dB)
140
120
MEDIAN
110
100
90
MIN
-20
0
20
40
60
80
150
130
MEDIAN
110
MIN
90
80
70
-40
n = 3000
100
70
-40
120
-20
0
FIGURE 25. ISL28271 CMRR vs TEMPERATURE, VCM = +2.5V
TO -2.5V
150
180
MAX
PSRR (dB)
PSRR (dB)
120
110
MEDIAN
90
80
100
120
n = 3000
MAX
140
120
MEDIAN
100
MIN
MIN
-20
0
20
40
60
80
100
60
-40
120
-20
0
TEMPERATURE (°C)
20
40
60
80
100
120
TEMPERATURE (°C)
FIGURE 27. ISL28271 PSRR vs TEMPERATURE, V+, V- = ±1.2V
TO ±2.5V
FIGURE 28. ISL28272 PSRR vs TEMPERATURE, V+, V- = ±1.2V
TO ±2.5V
4.91
4.91
n = 3000
n = 3000
4.90
4.90
MAX
MAX
4.89
VOUT (V)
4.89
VOUT (V)
80
80
70
60
-40
60
160
130
100
40
FIGURE 26. ISL28272 CMRR vs TEMPERATURE, VCM = +2.5V
TO -2.5V
n = 3000
140
20
TEMPERATURE (°C)
TEMPERATURE (°C)
4.88
4.87
MEDIAN
4.88
MEDIAN
4.87
MIN
4.86
4.86
MIN
4.85
4.84
-40
4.85
-20
0
20
40
60
80
100
120
TEMPERATURE (°C)
FIGURE 29. ISL28271 VOUT HIGH vs TEMPERATURE, RL = 1k,
V+, V- = ±2.5V
Rev X.00
4.84
-40
-20
0
20
40
60
80
100
120
TEMPERATURE (°C)
FIGURE 30. ISL28272 VOUT HIGH vs TEMPERATURE, RL = 1k,
V+, V- = ±2.5V
Page 8 of 14
ISL28271, ISL28272
Typical Performance Curves
4.9980
n = 3000
4.9975
VOUT (V)
4.9970
MAX
4.9965
MIN
4.9955
4.9950
-40
4.9970
MAX
4.9965
-20
0
MIN
4.9955
20
40
60
80
TEMPERATURE (°C)
100
120
4.9950
-40
-20
0
180
170
n = 3000
170
MAX
VOUT (mV)
130
MEDIAN
120
MAX
140
130
120
MEDIAN
110
110
100
MIN
100
MIN
90
90
-40
-20
0
20
40
60
80
100
80
-40
120
-20
0
6.0
5.8
MAX
VOUT (mV)
5.0
4.8
5.0
4.8
4.4
4.2
4.2
0
20
40
60
80
100
TEMPERATURE (°C)
FIGURE 35. ISL28271 VOUT LOW vs TEMPERATURE,
RL = 100k, V+, V- = ±2.5V
Rev X.00
120
MEDIAN
MIN
4.6
MIN
-20
100
5.2
4.4
4.0
-40
80
MAX
5.4
MEDIAN
4.6
60
n = 3000
5.6
5.4
5.2
40
FIGURE 34. ISL28272 VOUT LOW vs TEMPERATURE, RL = 1k,
V+, V- = ±2.5V
n = 3000
5.6
20
TEMPERATURE (°C)
TEMPERATURE (°C)
FIGURE 33. ISL28271 VOUT LOW vs TEMPERATURE, RL = 1k,
V+, V- = ±2.5V
VOUT (mV)
120
150
140
5.8
100
n = 3000
160
150
6.0
20
40
60
80
TEMPERATURE (°C)
FIGURE 32. ISL28272 VOUT HIGH vs TEMPERATURE,
RL = 100k, V+, V- = ±2.5V
FIGURE 31. ISL28271 VOUT HIGH vs TEMPERATURE,
RL = 100k, V+, V- = ±2.5V
VOUT (mV)
MEDIAN
4.9960
4.9960
160
n = 3000
4.9975
MEDIAN
VOUT (V)
4.9980
V+ = +5V, V- = GND, VFB+ = 1/2V+, RL = Open, TA = +25°C, unless otherwise specified.
120
4.0
-40
-20
0
20
40
60
80
100
120
TEMPERATURE (°C)
FIGURE 36. ISL28272 VOUT LOW vs TEMPERATURE,
RL = 100k, V+, V- = ±2.5V
Page 9 of 14
ISL28271, ISL28272
Pin Descriptions
ISL28271
16 Ld QSOP
ISL28272
16 Ld QSOP
2, 15
2, 15
OUT_A,
OUT_B
Circuit 3
Output Voltage. A complementary Class AB common-source output stage drives
the output of each channel. When disabled, the outputs are in a high impedance
state.
3, 14
3, 14
FB+_A,
FB+_B
Circuit 1A,
Circuit 1B
Positive Feedback high impedance terminals. ISL28272 input circuit is shown in
Circuit 1A, and the ISL28271 input circuit is shown in Circuit 1B.
PIN NAME
EQUIVALENT
CIRCUIT
PIN FUNCTION
ISL28271: to avoid offset drift, it is recommended that the terminals of the
ISL28271 are not overdriven beyond 1V and the input current must never
exceed 5mA.
4, 13
4, 13
FB-_A,
FB-_B
Circuit 1A,
Circuit 1B
Negative Feedback high impedance terminals. The FB- pins connect to an
external resistor divider to individually set the desired gain of the in-amp.
ISL28272 input circuit is shown in Circuit 1A, and the ISL28271 input circuit is
shown in Circuit 1B.
ISL28271: to avoid offset drift, it is recommended that the terminals of the
ISL28271 are not overdriven beyond 1V and the input current must never
exceed 5mA.
5, 12
5, 12
IN-_A,
IN-_B
Circuit 1A,
Circuit 1B
High impedance Inverting input terminals. Connect to the low side of the input
source signal. ISL28272 input circuit is shown in Circuit 1A, and the ISL28271
input circuit is shown in Circuit 1B.
ISL28271: to avoid offset drift, it is recommended that the terminals of the
ISL28271 are not overdriven beyond 1V and the input current must never
exceed 5mA.
6, 11
6, 11
IN+_A,
IN+_B
Circuit 1A,
Circuit 1B
High impedance Non-inverting input terminals. Connect to the high side of the
input source signal. ISL28272 input circuit is shown in Circuit 1A, and the
ISL28271 input circuit is shown in Circuit 1B.
ISL28271: to avoid offset drift, it is recommended that the terminals of the
ISL28271 are not overdriven beyond 1V and the input current must never
exceed 5mA.
7, 10
7, 10
EN_A,
EN_B
Circuit 2
Active LOW logic pins. When pulled above 2V, the corresponding channel turns
off and OUT is high impedance. A channel is enabled when pulled below 0.8V.
Built-in pull downs define each EN pin LOW when left floating.
16
16
V+
Circuit 4
Positive Supply terminal shared by all channels.
8
8
V-
Circuit 4
Negative Supply terminal shared by all channels. Grounded for single supply
operation.
1, 9
1, 9
NC
No Connect, pins can be left floating or grounded.
V+
V+
IN+
FB+
INFB-
V+
LOGIC
PIN
CAPACITIVELY
COUPLED
ESD CLAMP
OUT
V-
V-
V-
CIRCUIT 1A
V+
CIRCUIT 2
VCIRCUIT 3
CIRCUIT 4
V+
INFB-
IN+
FB+
V-
CIRCUIT 1B
Rev X.00
Page 10 of 14
ISL28271, ISL28272
Application Information
Product Description
charts. IREC also cures the abrupt change and even reverse
polarity of the input bias current over the whole range of input.
The ISL28271 and ISL28272 are dual channel micropower
instrumentation amplifiers (in-amps) which deliver rail-to-rail
input amplification and rail-to-rail output swing. The in-amps
also deliver excellent DC and AC specifications while
consuming only about 120µA for both channels. Because the
independent pair of feedback terminals set the gain and adjust
the output zero level, the ISL28271 and ISL28272 achieve high
CMRR regardless of the tolerance of the gain setting resistors.
The ISL28271 is internally compensated for a minimum gain of
10. The ISL28272 is internally compensated for a minimum
gain of 100.
Output Stage and Output Voltage Range
EN pins are available to independently enable or disable a
channel. When all channels are off, current consumption is
down to typically 4µA.
VIN, the potential difference across IN+ and IN-, is replicated
(less the input offset voltage) across FB+ and FB-. The
function of the 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
in-amp gain is set by two external resistors, the feedback
resistor RF, and the gain resistor RG.
Input Protection
All input terminals and feedback terminals have internal ESD
protection diodes to both positive and negative supply rails,
limiting the input voltage to within one diode beyond the supply
rails. Input signals originating from low impedance sources
should have current limiting resistors in series with the IN+ and
IN- pins to prevent damaging currents during power supply
sequencing and other transient conditions. The ISL28272 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.
External series resistors may be used as an external protection
to limit excessive external voltage and current from damaging
the inputs. On the other hand, the ISL28271 has no clamps to
limit the differential voltage on the input terminals allowing
higher differential input voltages at lower gain applications. It is
recommended however, that the terminals of the ISL28271 are
not overdriven beyond 1V to avoid offset drift.
Input Stage and Input Voltage Range
The input terminals (IN+ and IN-) of the in-amps are a single
differential pair of CMOS 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 is rail-to-rail
regardless of the feedback terminal settings and regardless of
the gain settings. They are able to handle input voltages that
are at or slightly beyond the supply and ground sensing
making these in-amps well suited for single 5V down to 2.4V
supply systems.
The IREC enables rail-to-rail input amplification without the
problems usually associated with the dual differential stage
topology. The IREC ensures that there are no drastic changes
in offset voltage over the entire range of the input. See Input
Offset Voltage vs Common-Mode Input Voltage in performance
Rev X.00
A Class AB common-source output stage drives the output.
The pair of complementary MOSFET devices drive the output
VOUT to within a few millivolts of the supply rails. At a 100k
load, the PMOS sources current and pulls the output up to
4mV below the positive supply. 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 are internally limited to 31mA.
When disabled, the outputs are in a high impedance state.
Gain Setting
2.4V TO 5.5V
IN+
IN+
IN-
IN-
FB+
FB-
VCM
RG
+
V+
EN
EN
-
VOUT
+
-
VISL28271
ISL28272
RF
FIGURE 37. GAIN IS SET BY TWO EXTERNAL RESISTORS,
RF AND RG
VIN = IN+ – INRF
VOUT = 1 + -------- VIN
R
G
(EQ. 1)
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 because the output will be at ground.
Reference Connection
Unlike a three op amp in-amp realization, a finite series
resistance seen at the REF terminal does not degrade the high
CMRR performance eliminating the need for an additional
external buffer amplifier. Figure 38 uses the FB+ pin to provide
a high impedance REF terminal.
Page 11 of 14
ISL28271, ISL28272
2.4V TO 5.5V
IN+
IN+
IN-
IN-
FB+
FB-
2.9V to 5.5V
VCM
R1
+
+
-
V+
EN
EN
VOUT
ISL28271
VISL28271
ISL28272
RG
RF
FIGURE 38. GAIN SETTING AND REFERENCE CONNECTION
.
VIN = IN+ – INRF
RF
VOUT = 1 + -------- VIN + 1 + -------- VREF
R
R
G
G
(EQ. 2)
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 Figure 38.
The FB+ pin can also be connected to the other end of resistor,
RG. See Figure 39. Keeping the basic concept that the in-amp
maintains constant differential voltage across the input terminals
and feedback terminals (FB- - FB+) = (IN+ - IN-), the transfer
function of Figure 39 can be derived.
2.4V TO 5.5V
IN+
IN+
IN-
IN-
FB+
FB-
VCM
+
+
-
V+
EN
EN
ISL28271
VOUT
VISL28271
ISL28272
Because of the independent pair of feedback terminals
provided by the in-amps, the CMRR is not degraded by any
resistor mismatches. Hence, unlike a three op amp and
especially a two op amp in-amp realization, the ISL28271 and
ISL28272 reduce the cost of external components by allowing
the use of 1% or more tolerance resistors without sacrificing
CMRR performance. The CMRR will be typically 110dB
regardless of the tolerance of the resistors used. Instead, a
resistor mismatch results in a higher deviation from the
theoretical gain - Gain Error.
Gain Error and Accuracy
The gain error indicated in the “Electrical Specifications” table
on page 2 is the inherent gain error alone. The gain error
specification listed does not include 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:
RF
VOUT = 1 + -------- 1 E RG + E RF + E G VIN
R
G
(EQ. 5)
Where:
ERG = Tolerance of RG
ERF = Tolerance of RF
EG
= Gain Error of the ISL28271
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, the total gain error
would be:
TotalGainError = E RG + E RF + E G typical
Disable/Power-Down
RG
RF
FIGURE 39. REFERENCE CONNECTION WITH AN AVAILABLE
VREF
VIN = IN+ – INRS + RF
VOUT = 1 + ---------------------- + VREF
RG
Rev X.00
A finite resistance RS in series with the VREF source, adds an
output offset of VIN*(RS/RG). As the series resistance RS
approaches zero, Equation 3 is simplified to Equation 4 for
Figure 39. VOUT is simply shifted by an amount VREF.
TotalGainError = 0.01 + 0.01 + 0.005 = 2.5%
RS
VREF
(EQ. 4)
External Resistor Mismatches
REF
R2
RF
VOUT = 1 + -------- VIN + VREF
R
G
The ISL28271 and ISL28272 have an enable/disable pin for
each channel. They can be powered down to reduce the
supply current to typically 4µA when all channels are off. When
disabled, the corresponding output is in a high impedance
state. The active low EN pin has an internal pull down and
hence can be left floating and the in-amp enabled by default.
When the EN is connected to an external logic, the in-amp will
shutdown when EN pin is pulled above 2V, and will power up
when EN bar is pulled below 0.8V.
(EQ. 3)
Page 12 of 14
ISL28271, ISL28272
Unused Channels
The ISL28271 and ISL28272 are Dual channel op amps. If the
application only requires one channel when using the
ISL28271 or ISL28272, the user must configure the unused
channel to prevent it from oscillating. The unused channel will
oscillate if the input and output pins are floating. This will result
in higher than expected supply currents and possible noise
injection into the channel being used. The proper way to
prevent this oscillation is to configure the feedback pins (FB+,
FB-) with the minimum gain stable values for the amplifier with
RF and RG resistors and tieing the input terminals to ground
(as shown in Figure 40).
IN+
INFB+
FB-
RG
+
+
RF
FIGURE 40. PREVENTING OSCILLATIONS IN UNUSED
CHANNELS
Rev X.00
Page 13 of 14
ISL28271, ISL28272
Quarter Size Outline Plastic Packages Family (QSOP)
MDP0040
A
QUARTER SIZE OUTLINE PLASTIC PACKAGES FAMILY
D
(N/2)+1
N
INCHES
SYMBOL QSOP16 QSOP24 QSOP28 TOLERANCE NOTES
E
PIN #1
I.D. MARK
E1
1
(N/2)
B
0.010
C A B
e
H
C
SEATING
PLANE
0.007
0.004 C
b
C A B
A
0.068
0.068
0.068
Max.
-
A1
0.006
0.006
0.006
±0.002
-
A2
0.056
0.056
0.056
±0.004
-
b
0.010
0.010
0.010
±0.002
-
c
0.008
0.008
0.008
±0.001
-
D
0.193
0.341
0.390
±0.004
1, 3
E
0.236
0.236
0.236
±0.008
-
E1
0.154
0.154
0.154
±0.004
2, 3
e
0.025
0.025
0.025
Basic
-
L
0.025
0.025
0.025
±0.009
-
L1
0.041
0.041
0.041
Basic
-
N
16
24
28
Reference
Rev. F 2/07
NOTES:
L1
A
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.
c
SEE DETAIL "X"
3. Dimensions “D” and “E1” are measured at Datum Plane “H”.
4. Dimensioning and tolerancing per ASME Y14.5M-1994.
0.010
A2
GAUGE
PLANE
L
A1
4°±4°
DETAIL X
© Copyright Intersil Americas LLC 2006-2007. All Rights Reserved.
All trademarks and registered trademarks are the property of their respective owners.
For additional products, see www.intersil.com/en/products.html
Intersil products are manufactured, assembled and tested utilizing ISO9001 quality systems as noted
in the quality certifications found at www.intersil.com/en/support/qualandreliability.html
Intersil products are sold by description only. Intersil may modify the circuit design and/or specifications of products at any time without notice, provided that such
modification does not, in Intersil's sole judgment, affect the form, fit or function of the product. Accordingly, the reader is cautioned to verify that datasheets 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
Rev X.00
Page 14 of 14
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