INA155
1999 Burr-Brown Corporation
PDS-1529A
Printed in U.S.A. October, 1999
FEATURES
q
RAIL-TO-RAIL OUTPUT SWING: Within 10mV
q
LOW OFFSET VOLTAGE:
200
V
q
LOW OFFSET DRIFT:
5
V/
C
q
INTERNAL FIXED GAIN = 10V/V OR 50V/V
q
SPECIFIED TEMPERATURE RANGE:
55
C to +125
C
q
LOW INPUT BIAS CURRENT: 0.2pA
q
WIDE BANDWIDTH: 550kHz in G = 10
q
HIGH SLEW RATE: 6.5V/
s
q
LOW COST
q
SO-8 AND TINY MSOP-8 PACKAGES
Single-Supply, Rail-to-Rail Output, CMOS
INSTRUMENTATION AMPLIFIER
DESCRIPTION
The INA155 is a low-cost CMOS instrumentation
amplifier with rail-to-rail output swing optimized for
low voltage, single-supply operation.
Wide bandwidth (550kHz in G = 10) and high slew
rate (6.5V/
s) make the INA155 suitable for driving
sampling A/D converters as well as general purpose
and audio applications. Fast settling time allows use
with higher speed sensors and transducers and rapid
scanning data acquisition systems.
APPLICATIONS
q
INDUSTRIAL SENSOR AMPLIFIERS
Bridge, RTD, Thermocouple, Flow, Position
q
MEDICAL EQUIPMENT
ECG, EEG, EMG Amplifiers
q
DRIVING A/D CONVERTERS
q
PCMCIA CARDS
q
AUDIO PROCESSING
q
COMMUNICATIONS
q
TEST EQUIPMENT
q
LOW COST AUTOMOTIVE INSTRUMENTATION
International Airport Industrial Park Mailing Address: PO Box 11400, Tucson, AZ 85734 Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 Tel: (520) 746-1111
Twx: 910-952-1111 Internet: http://www.burr-brown.com/ Cable: BBRCORP Telex: 066-6491 FAX: (520) 889-1510 Immediate Product Info: (800) 548-6132
INA155
INA155
For most current data sheet and other product
information, visit www.burr-brown.com
Gain can be set to 10V/V or 50V/V by pin strapping.
Gains between these two values can be obtained with
the addition of a single resistor. The INA155 is fully
specified over the supply range of +2.7 to +5.5V.
The INA155 is available in MSOP-8 and SO-8 sur-
face-mount packages. Both are specified for operation
over the temperature range 55
C to 125
C.
22.2k
200k
V
IN
V
IN
+
Ref
R
G
INA155
V
O
22.2k
5k
5k
200k
R
G
V+
V
1
5
2
3
8
7
4
6
A1
A2
G = 10 pins open
G = 50 pins connected
V
O
= (V
IN
V
IN
) G + V
REF
+
2
INA155
SPECIFICATIONS: V
S
= +2.7V to +5.5V
Boldface limits apply over the specified temperature range, T
A
= 40
C to +85
C
At T
A
= +25
C, R
L
= 10k
connected to V
S
/2. R
G
pins open (G = 10), and Ref = V
S
/2, unless otherwise noted.
INA155E, U
INA155EA, UA
PARAMETER
CONDITION
MIN
TYP
MAX
MIN
TYP
MAX
UNITS
INPUT
Offset Voltage, RTI
V
OS
V
S
= +5.0V, V
CM
= V
S
/2
0.2
1
V
V
mV
Over Temperature
1.5
V
mV
Drift
dV
OS
/d
T
5
V
V/
C
vs Power Supply
PSRR
V
S
= +2.7V to +6V, V
CM
= 0.2 V
S
50
200
V
V
V/ V
Over Temperature
250
V
V/V
vs Time
0.4
V
V/mo
INPUT VOLTAGE RANGE
Safe Input Voltage
(V) 0.5
(V+) + 0.5
V
V
V
Common-Mode Range
(1)
V
CM
V
S
= 5.5V
0.3
5.2
(2)
V
V
V
V
S
= 2.7V
0.15
2.5
(2)
V
V
V
Common-Mode Rejection Ratio
CMRR
V
S
= 5.5V, 0.6V < V
CM
< 3.7V, G = 10
92
100
80
V
dB
Over Temperature
85
79
dB
V
S
= 5.5V,0.6V < V
CM
< 3.7V, G = 50
86
90
77
V
dB
Over Temperature
85
76
dB
INPUT IMPEDANCE
Differential
10
13
|| 3
V
|| pF
Common-Mode
10
13
|| 3
V
|| pF
INPUT BIAS CURRENT
Input Bias Current
I
B
1
10
V
V
pA
Offset Current
I
OS
1
10
V
V
pA
NOISE, RTI
R
S
= 0
, G = 10 or 50
Voltage Noise: f = 0.1Hz to 10Hz
4.5
V
V/Vp-p
Voltage Noise Density: f = 10Hz
260
V
nV/
Hz
f = 100Hz
99
V
nV/
Hz
f = 1kHz
40
V
nV/
Hz
Current Noise: f = 1kHz
2
V
fA/
Hz
GAIN
10
50
V
V
V/V
Gain Equation
G = 10 + 400k
/(10k
+ R
G
)
V
V/V
Gain Error
(3)
V
S
= 5.5V, V
O
= 0.01V to 5.49V, G = 10
0.02
0.1
V
V
%
vs Temperature
2
10
V
V
ppm/
C
V
S
= 5.5V, V
O
= 0.05V to 5.45V, G = 50
0.05
0.25
V
V
%
vs Temperature
15
30
V
V
ppm/
C
Nonlinearity
V
S
= 5.5V, G = 10 or 50
0.005
0.05
% of FSR
Over Temperature
0.05
V
% of FSR
OUTPUT
Voltage Output Swing from Rail
R
L
= 10k
, G
ERR
< 0.1%
5
10
V
V
mV
Over Temperature
10
V
mV
Short-Circuit Current
Short Circuit to Ground
50
V
mA
Capacitance Load (stable operation)
See Typical Curve
V
FREQUENCY RESPONSE
Bandwidth, 3dB
BW
G = 10
550
V
kHz
G = 50
110
V
kHz
Slew Rate
SR
V
S
= 5.5V, C
L
= 100pF
6.5
V
V/
s
Settling Time: 0.1%
t
S
V
S
= 5.5V, V
O
= 2V Step, C
L
= 100pF, G = 10
5
V
s
V
S
= 5.5V, V
O
= 2V Step, C
L
= 100pF, G = 50
11
V
s
0.01%
V
S
= 5.5V, V
O
= 2V Step, C
L
= 100pF, G = 10
8
V
s
V
S
= 5.5V, V
O
= 2V Step, C
L
= 100pF, G = 50
15
V
s
Overload Recovery
50% Input Overload
0.2
V
s
Total Harmonic Distortion + Noise
THD+N
See Typical Curve
V
POWER SUPPLY
Specified Voltage Range
+2.7
+5.5
V
V
V
Operating Voltage Range
+2.5 to +6
V
V
Quiescent Current
V
IN
= 0, I
O
= 0
1.7
2.1
V
V
mA
Over Temperature
V
IN
= 0, I
O
= 0
2.6
V
mA
TEMPERATURE RANGE
Specified Range
40
+85
V
V
C
Operating Range
65
+150
V
V
C
Storage Range
65
+150
V
V
C
Thermal Resistance
JA
MSOP-8 Surface Mount
150
V
C/W
SO-8 Surface Mount
150
V
C/W
V
Same as INA155E, U.
NOTES: (1) For further information, refer to typical performance curves on common-mode input range. (2) Operation beyond (V+) 1.8V (max) results in reduced common-mode
rejection. See discussion and Figure 6 in the text of this data sheet. (3) Does not include error and TCR of additional optional gain-setting resistor in series with R
G
, if used.
3
INA155
SPECIFICATIONS: V
S
= +2.7V to +5.5V
Boldface limits apply over the specified temperature range, T
A
= 55
C to +125
C
At T
A
= +25
C, R
L
= 10k
connected to V
S
/2. R
G
pins open (G = 10), and Ref = V
S
/2, unless otherwise noted.
INA155E, U
INA155EA, UA
PARAMETER
CONDITION
MIN
TYP
MAX
MIN
TYP
MAX
UNITS
INPUT
Offset Voltage, RTI
V
OS
V
S
= +5.0V, V
CM
= V
S
/2
0.2
1
V
V
mV
Over Temperature
2
V
mV
Drift
dV
OS
/d
T
5
V
V/
C
vs Power Supply
PSRR
V
S
= +2.7V to +6V, V
CM
= 0.2 V
S
50
200
V
V
V/ V
Over Temperature
250
V
V/V
vs Time
0.4
V
V/mo
INPUT VOLTAGE RANGE
Safe Input Voltage
(V) 0.5
(V+) + 0.5
V
V
V
Common-Mode Range
(1)
V
CM
V
S
= 5.5V
0.3
5.2
(2)
V
V
V
V
S
= 2.7V
0.15
2.5
(2)
V
V
V
Common-Mode Rejection Ratio
CMRR
V
S
= 5.5V, 0.6V < V
CM
< 3.7V, G = 10
92
100
80
V
dB
Over Temperature
82
78
dB
V
S
= 5.5V, 0.6V < V
CM
< 3.7V, G = 50
86
90
77
V
dB
Over Temperature
84
76
dB
INPUT IMPEDANCE
Differential
10
13
|| 3
V
|| pF
Common-Mode
10
13
|| 3
V
|| pF
INPUT BIAS CURRENT
Input Bias Current
I
B
1
10
V
V
pA
Offset Current
I
OS
1
10
V
V
pA
NOISE, RTI
R
S
= 0
, G = 10 or 50
Voltage Noise: f = 0.1Hz to 10Hz
4.5
V
V/Vp-p
Voltage Noise Density: f = 10Hz
260
V
nV/
Hz
f = 100Hz
99
V
nV/
Hz
f = 1kHz
40
V
nV/
Hz
Current Noise: f = 1kHz
2
V
fA/
Hz
GAIN
10
50
V
V
V/V
Gain Equation
G = 10 + 400k
/(10k
+ R
G
)
V
V/V
Gain Error
(3)
V
S
= 5.5V, V
O
= 0.01V to 5.49V, G = 10
0.02
0.1
V
V
%
vs Temperature
2
10
V
V
ppm/
C
V
S
= 5.5V, V
O
= 0.05V to 5.45V, G = 50
0.05
0.25
V
V
%
vs Temperature
15
30
V
V
ppm/
C
Nonlinearity
V
S
= 5.5V, G = 10 or 50
0.005
0.05
% of FSR
Over Temperature
0.05
V
% of FSR
OUTPUT
Voltage Output Swing from Rail
R
L
= 10k
, G
ERR
< 0.1%
5
10
V
V
mV
Over Temperature
10
V
mV
Short-Circuit Current
Short Circuit to Ground
50
V
mA
Capacitance Load (stable operation)
See Typical Curve
V
FREQUENCY RESPONSE
Bandwidth, 3dB
BW
G = 10
550
V
kHz
G = 50
110
V
kHz
Slew Rate
SR
V
S
= 5.5V, C
L
= 100pF
6.5
V
V/
s
Settling Time: 0.1%
t
S
V
S
= 5.5V, V
O
= 2V Step, C
L
= 100pF, G = 10
5
V
s
V
S
= 5.5V, V
O
= 2V Step, C
L
= 100pF, G = 50
11
V
s
0.01%
V
S
= 5.5V, V
O
= 2V Step, C
L
= 100pF, G = 10
8
V
s
V
S
= 5.5V, V
O
= 2V Step, C
L
= 100pF, G = 50
15
V
s
Overload Recovery
50% Input Overload
0.2
V
s
Total Harmonic Distortion + Noise
THD+N
See Typical Curve
V
POWER SUPPLY
Specified Voltage Range
+2.7
+5.5
V
V
V
Operating Voltage Range
+2.5 to +6
V
V
Quiescent Current
V
IN
= 0, I
O
= 0
1.7
2.1
V
V
mA
Over Temperature
V
IN
= 0, I
O
= 0
2.8
V
mA
TEMPERATURE RANGE
Specified Range
55
+125
V
V
C
Operating Range
65
+150
V
V
C
Storage Range
65
+150
V
V
C
Thermal Resistance
JA
MSOP-8 Surface Mount
150
V
C/W
SO-8 Surface Mount
150
V
C/W
V
Same as INA155E, U.
NOTES: (1) For further information, refer to typical performance curves on common-mode input range. (2) Operation beyond (V+) 1.8V (max) results in reduced common-mode
rejection. See discussion and Figure 6 in the text of this data sheet. (3) Does not include error and TCR of additional optional gain-setting resistor in series with R
G
, if used.
4
INA155
PIN CONFIGURATION
ELECTROSTATIC
DISCHARGE SENSITIVITY
This integrated circuit can be damaged by ESD. Burr-Brown
recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling
and installation procedures can cause damage.
ESD damage can range from subtle performance degradation
to complete device failure. Precision integrated circuits may
be more susceptible to damage because very small parametric
changes could cause the device not to meet its published
specifications.
The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes
no responsibility for the use of this information, and all use of such information shall be entirely at the user's own risk. Prices and specifications are subject to change
without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant
any BURR-BROWN product for use in life support devices and/or systems.
Top View
SO-8 (U), MSOP-8 (E)
Supply Voltage, V+ to V ................................................................... 7.5V
Signal Input Terminals, Voltage
(2)
.................. (V) 0.5V to (V+) + 0.5V
Current
(2)
.................................................... 10mA
Output Short-Circuit
(3)
.............................................................. Continuous
Operating Temperature .................................................. 65
C to +150
C
Storage Temperature ..................................................... 65
C to +150
C
Junction Temperature .................................................................... +150
C
Lead Temperature (soldering, 10s) ............................................... +300
C
NOTE: (1) Stresses above these ratings may cause permanent damage.
Exposure to absolute maximum conditions for extended periods may degrade
device reliability. These are stress ratings only, and functional operation of the
device at these or any other conditions beyond those specified is not implied.
(2) Input terminals are diode-clamped to the power supply rails. Input signals
that can swing more that 0.5V beyond the supply rails should be current limited
to 10mA or less. (3) Short circuit to ground.
ABSOLUTE MAXIMUM RATINGS
(1)
PACKAGE
SPECIFIED
DRAWING
TEMPERATURE
PACKAGE
ORDERING
TRANSPORT
PRODUCT
PACKAGE
NUMBER
RANGE
MARKING
NUMBER
(1)
MEDIA
INA155U
SO-8
182
55
C to +125
C
INA155U
INA155U
Rails
"
"
"
"
"
INA155U/2K5
Tape and Reel
INA155UA
SO-8
182
55
C to +125
C
INA155UA
INA155UA
Rails
"
"
"
"
"
INA155UA/2K5
Tape and Reel
INA155E
MSOP-8
337
55
C to +125
C
A55
INA155E/250
Tape and Reel
"
"
"
"
"
INA155E/2K5
Tape and Reel
INA155EA
MSOP-8
337
55
C to +125
C
A55
INA155EA/250
Tape and Reel
"
"
"
"
"
INA155EA/2K5
Tape and Reel
NOTES: (1) Models with a slash (/) are available only in Tape and Reel in the quantities indicated (e.g., /2K5 indicates 2500 devices per reel). Ordering 2500 pieces
of "INA155UA/2K5" will get a single 2500-piece Tape and Reel.
PACKAGE/ORDERING INFORMATION
R
G
V
IN
V
IN
V
R
G
V+
V
OUT
Ref
1
2
3
4
8
7
6
5
INA155
+
5
INA155
TYPICAL PERFORMANCE CURVES
At T
A
= +25
C, V
S
= 5.5V, R
L
= 10k
connected to V
S
/2. R
G
pins open (G = 10), and Ref = V
S
/2, unless otherwise noted.
GAIN vs FREQUENCY
Frequency (Hz)
Gain (dB)
1
100
10
1k
10k
1M
10M
40
35
30
25
20
15
10
5
0
100k
G = 50
G =10
COMMON-MODE REJECTION RATIO vs FREQUENCY
Frequency (Hz)
CMRR (dB)
0.1
1
10
10k
100k
120
100
80
60
40
20
0
100
1k
G = 10
G = 50
POWER SUPPLY REJECTION RATIO vs FREQUENCY
Frequency (Hz)
PSRR (dB)
1
10
10k
100k
1M
100
90
80
70
60
50
40
30
20
10
0
100
1k
MAXIMUM OUTPUT VOLTAGE vs FREQUENCY
Frequency (Hz)
Maximum Output Voltage (Vp-p)
1
10
10k
100k
1M
6
5
4
3
2
1
0
100
1k
V
S
= 5.5V
SHORT-CIRCUIT CURRENT AND QUIESCENT CURRENT
vs POWER SUPPLY
Supply Voltage (V)
I
SC
(mA)
2.5
3
4.0
3.5
55
50
45
40
35
30
25
I
Q
(mA)
1.8
1.75
1.7
1.65
1.6
1.55
1.5
4.5
5.5
6
5
I
Q
+I
SC
I
SC
QUIESCENT CURRENT AND SHORT-CIRCUIT CURRENT
vs TEMPERATURE
Temperature (
C)
I
Q
(mA)
Short-Circuit Current (mA)
75
50
0
25
2.5
2.0
1.5
1.0
0.5
0
100
80
60
40
20
0
25
100
125
150
50
75
I
Q
+I
SC
I
SC
6
INA155
TYPICAL PERFORMANCE CURVES
(Cont.)
At T
A
= +25
C, V
S
= 5.5V, R
L
= 10k
connected to V
S
/2. R
G
pins open (G = 10), and Ref = V
S
/2, unless otherwise noted.
0.1Hz TO 10Hz VOLTAGE NOISE
500ms/div
1
V/div
Input-Referred
TOTAL HARMONIC DISTORTION + NOISE
vs FREQUENCY
1
0.1
0.01
0.001
THD+N (%)
10
100
10k
1k
Frequency (Hz)
R
L
= 600
R
L
= 600
R
L
= 10k
R
L
= 2k
G = 50
G = 10
R
L
=10k
R
L
= 2k
INPUT BIAS CURRENT vs TEMPERATURE
Temperature (
C)
Input Bias Current (pA)
75
50
25
0
10k
1k
100
10
1
0.1
25
100
125
150
50
75
SLEW RATE vs POWER SUPPLY
Supply Voltage (V)
Slew Rate (V
s)
2.5
3
4
3.5
7
6.5
6
5.5
5
4.5
4
4.5
6
5
5.5
SLEW RATE vs TEMPERATURE
Temperature (
C)
Slew Rate (V/
s)
75
50
0
25
10
9
8
7
6
5
4
3
2
1
0
25
100
125
150
50
75
INPUT VOLTAGE AND CURRENT NOISE DENSITY
vs FREQUENCY
Frequency (Hz)
Voltage Noise (nV/
Hz)
0.1
1
10
10k
1k
100
10
100
10
1
0.1
100
100k
1k
10k
Current Noise (fA/
Hz)
e
n
i
n
7
INA155
TYPICAL PERFORMANCE CURVES
(Cont.)
At T
A
= +25
C, V
S
= 5.5V, R
L
= 10k
connected to V
S
/2. R
G
pins open (G = 10), and Ref = V
S
/2, unless otherwise noted.
OFFSET VOLTAGE
PRODUCTION DISTRIBUTION
Percent of Amplifiers (%)
Offset Voltage (mV)
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
14
12
10
8
6
4
2
0
SETTLING TIME vs LOAD CAPACITANCE
Load Capacitance (pF)
Settling Time (
s)
10
100
10k
20
18
16
14
12
10
8
6
4
2
0
1k
0.01%, G = 50
0.1%, G = 50
0.01%, G = 10
0.1%, G = 10
OVERSHOOT vs LOAD CAPACITANCE
Load Capacitance (pF)
Overshoot (%)
10
100
10k
60
50
40
30
20
10
0
1k
G = 10
G = 50
5
s/div
100mV/div
SMALL-SIGNAL STEP RESPONSE
G = 10, C
L
= 100pF, R
L
= 10k
5
s/div
100mV/div
SMALL-SIGNAL STEP RESPONSE
G = 50, C
L
= 100pF, R
L
= 10k
OFFSET VOLTAGE DRIFT
PRODUCTION DISTRIBUTION
Percent of Amplifiers (%)
Offset Voltage Drift (
V/
C)
20
18
16
14
12
10
8
6
4
2
0
2
4
6
8
10
12
14
16
18
20
18
16
14
12
10
8
6
4
2
0
8
INA155
TYPICAL PERFORMANCE CURVES
(Cont.)
At T
A
= +25
C, V
S
= 5.5V, R
L
= 10k
connected to V
S
/2. R
G
pins open (G = 10), and Ref = V
S
/2, unless otherwise noted.
1
s/div
1V/div
LARGE-SIGNAL STEP RESPONSE
G = 10, G = 50, C
L
= 100pF, R
L
= 10k
INPUT COMMON-MODE RANGE
vs OUTPUT VOLTAGE, G = 50
V
OUT
(V)
V
CM
(V)
0
0.5
1
2
1.5
6
5
4
3
2
1
0
2.5
5.5
3
3.5
4
4.5
5
Ref = 0V
Ref = 2.75V
Ref = 5.5V
G = 50
0.9V + 0.04V
OUT
+ 0.06Ref < V
CM
< 0.9V
+
+ 0.04V
OUT
+ 0.06Ref
5ms/div
1V/div
COMMON-MODE REJECTION AT 60Hz
2mV/div
INPUT COMMON-MODE RANGE
vs REFERENCE VOLTAGE, G = 10
V
REF
(V)
V
CM
(V)
0
0.5
1
2
1.5
6
5
4
3
2
1
0
2.5
5.5
3
3.5
4
4.5
5
G = 10
0.9V
+ 0.1V
REF
< V
CM
< 0.9V
+
0.1Ref
9
INA155
APPLICATIONS INFORMATION
Figure 1 shows the basic connections required for operation
of the INA155. Applications with noisy or high impedance
power supplies may require decoupling capacitors close to
the device pins as shown.
The output is referred to the output reference terminal, Ref,
which is normally set to V
S
/2. This must be a low-imped-
ance connection to ensure good common-mode rejection. A
resistance of 200
in series with the Ref pin will cause a
typical device to degrade to approximately 80dB CMRR.
In addition, for the G = 50 configuration, the connection
between pins 1 and 8 must be low-impedance. A connection
impedance of 20
can cause a 0.2% shift in gain error.
OPERATING VOLTAGE
The INA155 is fully specified and guaranteed over the supply
range +2.7V to +5.5V, with key parameters guaranteed over
the temperature range of 55
C to +125
C. Parameters that
vary significantly with operating voltages, load conditions or
temperature are shown in the Typical Performance Curves.
The INA155 can be operated from either single or dual
power supplies. By adjusting the voltage applied to the
reference terminal, the input common-mode voltage range
and the output range can be adjusted within the bounds
shown in the Typical Performance Curves. Figure 2 shows
a bridge amplifier circuit operated from a single +5V power
supply. The bridge provides a relatively small differential
voltage on top of an input common-mode voltage near 2.5V.
FIGURE 1. Basic Connections.
FIGURE 2. Single-Supply Bridge Amplifier.
Bridge
Sensor
INA155
V
REF
(1)
+5V
3
2
4
5
7
6
V
OUT
= 0.01V to 4.99V
(2)
NOTES: (1) V
REF
should be adjusted for the desired output level,
keeping in mind that the value of V
REF
affects the common-mode
input range. See Typical Performance Curve. (2) For best
performance, the common-mode input voltage should be kept away
from the transition range of (V+) 1.8V to (V+) 0.8V.
1
8
V
IN
+
V
IN
Ref
22.2k
200k
5k
Gain Pins Open:
G = 10
External Resistor R
G
:
10 < G < 50
Gain Pins Connected:
G = 50
5k
200k
22.2k
4
3
2
5
7
1
8
V
0.1
F
Single Supply
Also drawn in simplified form:
Dual Supply
INA155
INA155
6
1
3
8
2
V
OUT
6
7
4
5
Ref
0.1
F
V+
V+
V
DESIRED GAIN
R
G
(V/V)
(
)
10
Open
20
30k
30
10k
40
3.3k
50
Short
G = 10 +
400k
10k
+ R
G
V
IN
V
IN
+
A1
A2
V
IN
+
V
IN
V
OUT
= (V
IN
V
IN
) G + V
REF
+
10
INA155
SETTING THE GAIN
Gain of 10 is achieved simply by leaving the two gain pins
(1 and 8) open. Gain of 50 is achieved by connecting the
gain pins together directly. In the G = 10 configuration, the
gain error is less than 0.1%. In the G = 50 configuration, the
gain error is less than 0.25%.
Gain can be set to any value between 10 and 50 by connect-
ing a resistor R
G
between the gain pins according to the
following equation:
10 + 400k
/(10k
+ R
G
)
(1)
This is demonstrated in Figure 1 and is shown with the com-
monly used gains and resistor R
G
values. However, because the
absolute value of internal resistors is not guaranteed, using the
INA155 in this configuration will increase the gain error and
gain error drift with temperature, as shown in Figure 3.
FIGURE 3. Typical Gain Error and Gain Error Drift with
External Resistor.
OFFSET TRIMMING
The INA155 is laser trimmed for low offset voltage. In most
applications, no external offset adjustment is required. How-
ever, if necessary, the offset can be adjusted by applying a
correction voltage to the reference terminal. Figure 4 shows
an optional circuit for trimming the output offset voltage.
The voltage applied to the Ref terminal is added to the
output signal. An op amp buffer is used to provide low
impedance at the Ref terminal to preserve good common-
mode rejection.
INPUT BIAS CURRENT RETURN
The input impedance of the INA155 is extremely high--
approximately 10
13
, making it ideal for use with high-imped-
ance sources. However, a path must be provided for the input
bias current of both inputs. This input bias current is less than
10pA and is virtually independent of the input voltage.
Input circuitry must provide a path for this input bias current
for proper operation. Figure 5 shows various provisions for
an input bias current path. Without a bias current path, the
inputs will float to a potential that exceeds the common-
mode range and the input amplifier will saturate.
If the differential source resistance is low, the bias current
return path can be connected to one input (see the thermo-
couple in Figure 5). With higher source impedance, using
two equal resistors provides a balanced input with advan-
tages of lower input offset voltage due to bias current and
better high-frequency common-mode rejection.
FIGURE 4. Optional Trimming of Output Offset Voltage.
FIGURE 5. Providing an Input Common-Mode Current Path.
10k
OPA336
10mV
Adjustment Range
100
100
100
A
1/2 REF200
100
A
1/2 REF200
V+
V
INA155
Ref
3
6
2
5
V
O
V
REF
(1)
V
IN
+
(2)
V
IN
(2)
NOTES: (1) V
REF
should be adjusted for the
desired output level. The value of V
REF
affects the common-mode input range. (2)
For best performance, common-mode input
voltage should be less than (V+) 1.8V or
greater than (V+)
0.8V.
1
8
Gain (V/V)
Gain Error (%)
10
15
20
30
25
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
Gain Error Drift (ppm/
C)
400
360
320
280
250
200
160
120
80
40
0
35
40
50
45
Gain Error Drift
Gain Error
INA155
3
6
6
6
6
2
47k
5
V
REF
47k
Microphone,
Hydrophone, etc.
INA155
3
2
3
2
5
V
REF
Center-tap
provides bias
current return
Low-resistance
thermocouple
provides bias
current return.
Bridge resistance
provides bias
current return
INA155
3
2
10k
5
V
REF
Thermocouple
INA155
5
V
REF
Bridge
Sensor
1
8
1
8
1
8
1
8
11
INA155
INPUT COMMON-MODE RANGE
The input common-mode range of the INA155 for various
operating conditions is shown the in Typical Performance
Curves. The common-mode input range is limited by the
output voltage swing of A1, an internal circuit node. For the G
= 10 configuration, output voltage of A1 can be expressed as:
V
OUTA1
=
1
/
9
V
REF
+ (1 +
1
/
9
) V
IN
(2)
Using this equation given that the output of A1 can swing to
within 10mV of either rail, the input common-mode voltage
range can be calculated. When the input common-mode range
is exceeded (A1's output is saturated), A2 can still be in linear
operation and respond to changes in the non-inverting input
voltage. However, the output voltage will be invalid.
The common-mode range for the G = 50 configuration is
included in the Typical Performance Curve, "Input Com-
mon-Mode Range vs Output Voltage."
INPUT RANGE FOR BEST ACCURACY
The internal amplifiers have rail-to-rail input stages, achieved
by using complementary n- and p-channel input pairs. The
common-mode input voltage determines whether the
p-channel or the n-channel input stage is operating. The
transition between the input stages is gradual and occurs
between (V+) 1.8V to (V+) 0.8V. Due to these charac-
teristics operating the INA155 with input voltages within the
transition region of (V+) 1.8V to (V+) 0.8V results in a
shift in input offset voltage and reduced common-mode and
power supply rejection performance. Typical patterns of the
offset voltage change throughout the input common-mode
range are illustrated in Figure 6. The INA155 can be
operated below or above the transition region with excellent
results. Figure 7 demonstrates the use of the INA155 in a
single-supply, high-side current monitor. In this applica-
tion, the INA155 is operated above the transition region.
RAIL-TO-RAIL OUTPUT
A class AB output stage with common-source transistors
is used to achieve rail-to-rail output. For resistive loads
greater than 10k
, the output voltage can swing to within
a few millivolts of the supply rail while maintaining low
gain error. For heavier loads and over temperature, see the
typical performance curve "Output Voltage Swing vs Out-
put Current." The INA155's low output impedance at high
frequencies makes it suitable for directly driving Capaci-
tive Digital-to-Analog (CDAC) input A/D converters, as
shown in Figure 9.
INPUT PROTECTION
Device inputs are protected by ESD diodes that will conduct
if the input voltages exceed the power supplies by more than
500mV. Momentary voltages greater than 500mV beyond
the power supply can be tolerated if the current on the input
pins is limited to 10mA. This is easily accomplished with
input resistors R
LIM
as shown in Figure 8. Many input
signals are inherently current-limited to less than 10mA,
therefore, a limiting resistor is not required.
FIGURE 6. Input Offset Voltage Changes with Common-
Mode Voltage.
FIGURE 7. Single-Supply, High-Side Current Monitor.
FIGURE 8. Input Current Protection for Voltages Exceed-
ing the Supply Voltage.
Input Common-Mode Voltage (V)
Input Offset Voltage (mV)
0.0
0.5
1.0
2.5
3.0
1.5
2.0
1.00
0.80
0.60
0.40
0.20
0.00
0.20
0.40
0.60
0.80
0.100
3.5
4.0
5.5
4.5
5.0
Transistion
Region
P-Channel Operation
V
S
= 1.8V
V
S
= 5.5V
V
S
= 0.8V
N-Channel
Operation
FIGURE 9. INA155 Directly Drives Capacitive-Input,
High-Speed A/D Converter.
INA155
5
V
OUT
V
REF
R
LIM
R
LIM
I
OVERLOAD
10mA max
3
6
2
1
8
+5V
INA155
ADS7818
or
ADS7834
12-Bits
f
SAMPLE
= 500kHz
6
7
4
4
2
3
NOTE: G = 10 configuration
1
8
INA155
7
6
4
5
I
L
2.5A
G = 10
Pins 1 and 8 Open
V+
NOTE: Output is referred to V+.
2
3
1
8
0.02
Load
50mV
PDF 
ZIP