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Final Electrical Specifications
FEATURES
s s
LT1168 Low Power, Single Resistor Gain Programmable, Micropower Precision Instrumentation Amplifier DESCRIPTIO March 2000
The LT (R)1168 is a micropower, precision instrumentation amplifier that requires only one external resistor to set gains of 1 to 10,000. The low voltage noise of 10nV/Hz (at 1kHz) is not compromised by low power dissipation (350A typical for 15V supplies). The wide supply range of 2.3V to 18V allows the LT1168 to fit into a wide variety of industrial as well as battery-powered applications. The high accuracy of the LT1168 is due to a 20ppm maximum nonlinearity and 0.4% max gain error (G = 10). Previous monolithic instrumentation amps cannot handle a 2k load resistor whereas the nonlinearity of the LT1168 is specified for loads as low as 2k. The LT1168 is laser trimmed for very low input offset voltage (40V max), drift (0.3V/C), high CMRR (90dB, G = 1) and PSRR (103dB, G = 1). Low input bias currents of 250pA max are achieved with the use of superbeta processing. The output can handle capacitive loads up to 1000pF in any gain configuration while the inputs are ESD protected up to 13kV (human body). The LT1168 with two external 5k resistors passes the IEC 1000-4-2 level 4 specification. The LT1168 is a pin-for-pin improved second source for the AD620 and INA118. The LT1168, offered in 8-pin PDIP and SO packages, requires significantly less PC board area than discrete op amp resistor designs. These advantages make the LT1168 the most cost effective solution for precision instrumentation amplifier applications.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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Supply Current: 530A Max Meets IEC 1000-4-2 Level 4 ESD Tests with Two External 5k Resistors Single Gain Set Resistor: G = 1 to 10,000 Gain Error: G = 10, 0.4% Max Input Offset Voltage Drift: 0.3V/C Max Gain Nonlinearity: G = 10, 20ppm Max Input Offset Voltage: 40V Max Input Bias Current: 250pA Max PSRR at AV =1: 103dB Min CMRR at AV = 1: 90dB Min Wide Supply Range: 2.3V to 18V 1kHz Voltage Noise: 10nV/Hz 0.1Hz to 10Hz Noise: 0.28VP-P Available in 8-Pin PDIP and SO Packages
APPLICATIO S
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Bridge Amplifiers Strain Gauge Amplifiers Thermocouple Amplifiers Differential to Single-Ended Converters Differential Voltage to Current Converters Data Acquisition Battery-Powered and Portable Equipment Medical Instrumentation Scales
TYPICAL APPLICATIO
5V 1 3.5k 3.5k 3 8 R1 G = 200 249 1 2
Single Supply* Pressure Monitor
BI TECHNOLOGIES 67-8-3 R40KQ, (0.02% RATIO MATCH) NONLINEARITY (100ppm/DIV)
+
40k 7 REF LT1168 5 6 20k 3 40k 2 IN ADC LTC(R)1286 1 AGND DIGITAL DATA OUTPUT
3.5k
3.5k
-
+
1/2 LT1112
4
-
G = 1000
1168 TA01
*See Theory of Operation section Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
U
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Gain Nonlinearity
OUTPUT VOLTAGE (2V/DIV)
1168 TA01a
RL = 2K VOUT = 10V
1
LT1168
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
ORDER PART NUMBER
TOP VIEW RG 1 -IN 2 +IN 3 -VS 4 N8 PACKAGE 8-LEAD PDIP S8 PACKAGE 8-LEAD PLASTIC SO
TJMAX = 150C, JA = 130C/ W (N8) TJMAX = 150C, JA = 190C/ W (S8)
Supply Voltage ...................................................... 20V Differential Input Voltage (Within the Supply Voltage) ..................................................... 40V Input Voltage (Equal to Supply Voltage) ................ 20V Input Current (Note 2) ....................................... 20mA Output Short-Circuit Duration (Note 3) ............ Indefinite Operating Temperature Range (Note 4) .. - 40C to 85C Specified Temperature Range LT1168AC/LT1168C (Note 5) ............. - 40C to 85C LT1168AI/LT1168I ............................. - 40C to 85C Storage Temperature Range ................. - 40C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
8 - + 7 6 5
RG +VS OUTPUT REF
LT1168ACN8 LT1168ACS8 LT1168AIN8 LT1168AIS8 LT1168CN8 LT1168CS8 LT1168IN8 LT1168IS8 S8 PART MARKING 1168A 1168AI 1168 1168I
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
SYMBOL G PARAMETER Gain Range Gain Error
TA = 25C. VS = 15V, VCM = 0V, RL = 10k unless otherwise noted.
LT1168AC/LT1168AI MIN TYP MAX 1 0.008 0.04 0.04 0.08 2 10 20 4 20 40 15 40 90 40 10k 0.02 0.4 0.5 0.5 6 20 40 15 40 75 40 200 300 250 LT1168C/LT1168I MIN TYP MAX 1 0.015 0.05 0.05 0.08 3 15 25 5 30 50 20 50 100 80 2.00 0.28 15 220 10 165 5 74 200 1000 15 220 10k 0.03 0.5 0.6 0.6 10 25 60 20 60 90 60 300 450 500 % % % % ppm ppm ppm ppm ppm ppm V V pA pA VP-P VP-P nV/Hz nV/Hz pAP-P fA/Hz G UNITS
CONDITIONS (Note 6) G = 1 + (49.4k/RG) G=1 G = 10 (Note 7) G = 100 (Note 7) G = 1000 (Note 7) VO = 10V, G = 1 VO = 10V,G = 10 and 100 VO = 10V, G = 1000 VO = 10V, G = 1, RL = 2k VO = 10V,G = 10 and 100, RL = 2k VO = 10V, G = 1000, RL = 2k
Gain Nonlinearity (Notes 7, 8)
VOST VOSI VOSO IOS IB en
Total Input Referred Offset Voltage VOST = VOSI + VOSO/G Input Offset Voltage Output Offset Voltage Input Offset Current Input Bias Current Input Noise Voltage, RTI Input Noise Voltage Density, RTI 0.1Hz to 10Hz, G = 1 0.1Hz to 10Hz, G = 1000 fO = 1kHz G = 1000, VS = 5V to 15V G = 1, VS = 5V to 15V
2.00 0.28 10 165 5 74 300 1000
in RIN
Output Noise Voltage Density, RTI fO = 1kHz (Note 9) Input Noise Current fO = 0.1Hz to 10Hz Input Noise Current Density Input Resistance fO = 10Hz VIN = 10V
2
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W
U
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WW
W
LT1168
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER CIN(DIFF) CIN(CM) VCM Differential Input Capacitance Common Mode Input Capacitance Input Voltage Range fO = 100kHz fO = 100kHz
TA = 25C. VS = 15V, VCM = 0V, RL = 10k unless otherwise noted.
LT1168AC/LT1168AI MIN TYP MAX 1.6 1.6 LT1168C/LT1168I MIN TYP MAX 1.6 1.6 UNITS pF pF
CONDITIONS (Note 6)
G = 1, Other Input Grounded VS = 2.3V to 5V VS = 5V to 18V 1k Source Imbalance, VCM = 0V to 10V G=1 G = 10 G = 100 G = 1000 VS = 2.3V to 18V G=1 G = 10 G = 100 G = 1000 VS = 2.3V to 18V RL = 10k VS = 2.3V to 5V VS = 5V to 18V G=1 G = 10 G = 100 G = 1000 G = 1, VOUT = 10V 10V Step G = 1 to 100 G = 1000 VREF = 0V
-VS + 1.9 -VS + 1.9
+VS - 1.2 -VS + 1.9 +VS - 1.4 -VS + 1.9
+VS - 1.2 +VS - 1.4
V V
CMRR
Common Mode Rejection Ratio
90 106 120 126 103 122 131 135
95 115 135 140 108 128 145 150 350 530
85 100 110 120 100 118 126 130
95 115 135 140 108 128 145 150 350 530 +VS - 1.2 +VS - 1.3 27 400 200 13 1
dB dB dB dB dB dB dB dB A V V mA kHz kHz kHz kHz V/s s s k A +VS - 1.6 V
PSRR
Power Supply Rejection Ratio
IS VOUT
Supply Current Output Voltage Swing
-VS + 1.1 -VS + 1.2 20 27 400 200 13 1 0.3 0.5 30 200 60 18 -VS + 1.6 1 0.0001
+VS - 1.2 -VS + 1.1 +VS - 1.3 -VS + 1.2 20
IOUT BW
Output Current Bandwidth
SR
Slew Rate Settling Time to 0.01%
0.3
0.5 30 200 60 18
REFIN IREFIN VREF AVREF
Reference Input Resistance Reference Input Current Reference Voltage Range Reference Gain to Output
+VS - 1.6 -VS + 1.6 1 0.0001
The q denotes the specifications which apply over the 0C TA 70C temperature range. VS = 15V, VCM = 0V, RL = 10k unless otherwise noted.
SYMBOL PARAMETER Gain Error CONDITIONS (Note 6) G=1 G = 10 (Note 7) G = 100 (Note 7) G = 1000 (Note 7) VOUT = 10V, G = 1 VOUT = 10V, G = 10 and 100 VOUT = 10V, G = 1000 G < 1000 (Note 7)
q q q q q q q q
MIN
LT1168AC TYP 0.01 0.40 0.45 0.50 2 7 25 100
MAX 0.03 1.5 1.6 1.7 15 30 60 200
MIN
LT1168C TYP 0.012 0.500 0.550 0.600 3 10 30 100
MAX 0.04 1.6 1.7 1.8 20 35 80 200
UNITS % % % % ppm ppm ppm ppm/C
Gain Nonlinearity (Notes 7, 8) G/T Gain vs Temperature
3
LT1168
The q denotes the specifications which apply over the 0C TA 70C temperature range. VS = 15V, VCM = 0V, RL = 10k unless otherwise noted.
SYMBOL PARAMETER VOST VOSI VOSIH VOSO VOSOH VOSI/T VOSO/T IOS IOS/T IB IB/T VCM Input Offset Voltage Input Offset Voltage Hysteresis Output Offset Voltage Input Offset Drift (RTI) Output Offset Drift Input Offset Current Input Offset Current Drift Input Bias Current Input Bias Current Drift Input Voltage Range CONDITIONS (Note 6) VOST = VOSI + VOSO/G
q q q q q q q q q q
ELECTRICAL CHARACTERISTICS
MIN
LT1168AC TYP 18 3.0 60 30 0.05 0.7 100 0.3 65 1.4
MAX 60 380 0.3 3 400 350
MIN
LT1168C TYP 23 3.0 70 30 0.06 0.8 120 0.4 105 1.4
MAX 80 500 0.4 4 550 600
UNITS V V V V V/C V/C pA pA/C pA pA/C
Total Input Referred Offset Voltage
VS = 5V to 15V (Notes 7, 10) VS = 5V to 15V (Note 9) (Note 9)
Output Offset Voltage Hysteresis (Notes 7, 10)
G = 1, Other Input Grounded VS = 2.3V to 5V q -VS + 2.1 q -VS + 2.1 VS = 5V to 18V 1k Source Imbalance, VCM = 0V to 10V G=1 G = 10 G = 100 G = 1000 VS = 2.3V to 18V G=1 G = 10 G = 100 G = 1000 VS = 2.3V to 18V RL = 10k VS = 2.3V to 5V VS = 5V to 18V G = 1, VOUT = 10V (Note 9)
+VS - 1.3 -VS + 2.1 +VS - 1.4 -VS + 2.1
+VS - 1.3 +VS - 1.4
V V
CMRR
Common Mode Rejection Ratio
q q q q q q q q q
88 100 115 117 102 123 127 129
92 110 120 135 115 130 135 145 390 615
83 97 113 114 98 118 124 126
92 110 120 135 115 130 135 145 390 615 +VS - 1.3 +VS - 1.5 21 0.48 +VS - 1.6
dB dB dB dB dB dB dB dB A V V mA V/s V
PSRR
Power Supply Rejection Ratio
IS VOUT
Supply Current Output Voltage Swing
q -VS + 1.4 q -VS + 1.6 q q
IOUT SR VREF
Output Current Slew Rate Voltage Range
16 0.25
21 0.48
+VS - 1.3 -VS + 1.4 +VS - 1.5 -VS + 1.6 16 0.25 +VS - 1.6 -VS + 1.6
q -VS + 1.6
The q denotes the specifications which apply over the - 40C TA 85C temperature range. VS = 15V, VCM = 0V, RL = 10k unless otherwise noted. (Note 8)
SYMBOL PARAMETER Gain Error CONDITIONS (Note 6) G=1 G = 10 (Note 7) G = 100 (Note 7) G = 1000 (Note 7) VO = 10V, G = 1 VO = 10V, G = 10 and 100 VO = 10V, G = 1000 G < 1000 (Note 7)
q q q q q q q q
MIN
LT1168AI TYP 0.014 0.600 0.600 0.600 3 10 30 100
MAX 0.04 1.9 2.0 2.1 20 35 70 200
MIN
LT1168I TYP 0.015 0.700 0.700 0.700 5 15 35 100
MAX 0.05 2.0 2.1 2.2 25 40 100 200
UNITS % % % % ppm ppm ppm ppm/C
GN
Gain Nonlinearity (Notes 7, 8) Gain vs Temperature
G/T
4
LT1168
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER VOST VOSI VOSIH VOSO VOSOH VOSI/T VOSO/T IOS IOS/T IB IB/T VCM CMRR Input Offset Voltage Input Offset Voltage Hysteresis Output Offset Voltage Output Offset Voltage Hysteresis (Notes 7, 10) Input Offset Drift (RTI) Output Offset Drift Input Offset Current Input Offset Current Drift Input Bias Current Input Bias Current Drift Input Voltage Range Common Mode Rejection Ratio VS = 2.3V to 5V VS = 5V to 18V (Note 9) (Note 9) (Notes 7, 10)
The q denotes the specifications which apply over the - 40C TA 85C temperature range. VS = 15V, VCM = 0V, RL = 10k unless otherwise noted. (Note 5)
CONDITIONS (Note 6) VOST = VOSI + VOSO/G
q q q q q q q q q q q q
MIN
LT1168AI TYP 20 3.0 180 30 0.05 0.8 110 0.3 120 1.4
MAX 75 500 0.3 5 550 500
MIN
LT1168I TYP 25 3.0 200 30 0.06 1 120 0.3 220 1.4
MAX 100 600 0.4 6 700 800 +VS - 1.3 +VS - 1.4
UNITS V V V V V/C V/C pA pA/C pA pA/C V V
Total Input Referred Offset Voltage
-VS + 2.1 -VS + 2.1
+VS - 1.3 -VS + 2.1 +VS - 1.4 -VS + 2.1
1k Source Imbalance, VCM = 0V to 10V G=1 G = 10 G = 100 G = 1000 VS = 2.3V to 18V G=1 G = 10 G = 100 G = 1000 VS = 2.3V to 5V VS = 5V to 18V
q q q q q q q q q q q q q
86 98 114 116 100 120 125 128 -VS + 1.4 -VS + 1.6 15 0.22 -VS + 1.6
90 105 118 133 112 125 132 140 420 650
81 95 112 112 95 115 120 125 +VS - 1.3 -VS + 1.4 +VS - 1.5 -VS + 1.6 15 0.22 +VS - 1.6 -VS + 1.6
90 105 118 133 112 125 132 140 420 650 +VS - 1.3 +VS - 1.5 20 0.42 +VS - 1.6
dB dB dB dB dB dB dB dB A V V mA V/s V
PSRR
Power Supply Rejection Ratio
IS VOUT IOUT SR VREF
Supply Current Output Voltage Swing Output Current Slew Rate Voltage Range (Note 9)
20 0.41
q
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be imparied. Note 2: If the input voltage exceeds the supplies, the input current should be limited to less than 20mA. Note 3: A heat sink may be required to keep the junction temperature below absolute maximum. Note 4: The LT1168AC/LT1168C are guaranteed functional over the operating temperature range of - 40C and 85C. Note 5: The LT1168AC/LT1168C are guaranteed to meet specified performance from 0C to 70C. The LT1168AC/LT1168C are designed, characterized and expected to meet specified performance from - 40C and 85C but are not tested or QA sampled at these temperatures. The LT1168AI/LT1168I are guaranteed to meet specified performance from - 40C to 85C.
Note 6: Typical parameters are defined as the 60% of the yield parameter distribution. Note 7: Does not include the tolerance of the external gain resistor RG. Note 8: This parameter is measured in a high speed automatic tester that does not measure the thermal effects with longer time constants. The magnitude of these thermal effects are dependent on the package used, heat sinking and air flow conditions. Note 9: This parameter is not 100% tested. Note 10: Hysteresis in offset voltage is created by package stress that differs depending on whether the IC was previously at a higher or lower temperature. Offset voltage hysteresis is always measured at 25C, but the IC is cycled to 85C I-grade (or 70C C-grade) or - 40C I-grade (0C C-grade) before successive measurement. 60% of the parts will pass the typical limit on the data sheet.
5
LT1168 TYPICAL PERFOR A CE CHARACTERISTICS
Gain vs Frequency
60 50 40
GAIN (dB)
G = 1000
VOLTAGE NOISE DENSITY (nV/Hz)
VS = 15V TA = 25C
30 20
G = 100
100 1/f CORNER = 7Hz GAIN = 10 GAIN = 100, 1000 10 1/f CORNER = 3Hz BW LIMIT GAIN = 1000 1 10 100 1k FREQUENCY (Hz) BW LIMIT GAIN = 100
G = 10 10 0 G=1 -10 -20 0.01 0.1 1 10 FREQUENCY (kHz) 100 1000
1
NOISE VOLTAGE (2V/DIV)
0.1Hz to 10Hz Noise Voltage, RTI G = 1000
CURRENT NOISE DENSITY (fA/Hz) VS = 15V TA = 25C
NOISE VOLTAGE (0.2V/DIV)
100
1/f CORNER = 55Hz 10
NOISE CURRENT (5pA/DIV)
0
1
2
3
456 TIME (SEC)
7
Short-Circuit Current vs Time
50 40 VS = 15V
OUTPUT CURRENT (mA) (SINK) (SOURCE)
TA = - 40C
30 20 10 0 - 10 - 20 - 30 - 40 - 50
OUTPUT IMPEDANCE ()
TA = 25C TA = 85C
OVERSHOOT (%)
TA = 85C TA = 25C TA = - 40C
2 1 0 3 TIME FROM OUTPUT SHORT TO GROUND (MINUTES)
1168 G15
6
UW
LT1168 * G02
Voltage Noise Density vs Frequency
1000 1/f CORNER = 2Hz GAIN = 1 VS = 15V TA = 25C
0.1Hz to 10Hz Noise Voltage, G=1
VS = 15V TA = 25C
10k
100k
0
1
2
3
456 TIME (SEC)
7
8
9
10
LT1168 * G01
1168 G11
Current Noise Density vs Frequency
1000 VS = 15V TA = 25C
0.1Hz to 10Hz Current Noise
VS = 15V TA = 25C
RS
8
9
10
1
10 100 FREQUENCY (Hz)
1000
1168 G13
0
1
2
3
456 TIME (SEC)
7
8
9
10
1168 G12
1168 G14
Output Impedance vs Frequency
1k VS = 15V TA = 25C G = 1 TO 1000
100 90 80 70 60 50 40 30 20 10
Overshoot vs Capacitive Load
VS = 15V VOUT = 50mV RL =
100
10
G=1
1
G = 10
0.1 1k 10k 100k FREQUENCY (Hz) 1M
1168 G17
0 10
G = 100, 1000 100 1000 CAPACITIVE LOAD (pF) 10000
1168 G16
LT1168 TYPICAL PERFOR A CE CHARACTERISTICS
Settling Time vs Step Size
10 8 6 VS = 15 G=1 TA = 25C CL = 30pF RL = 1k
TO 0.1% TO 0.01%
SETTLING TIME (s)
OUTPUT STEP (V)
4 2 0 -2 -4 -6 -8 -10
100
SETTLING TIME (s)
0V 0V
TO 0.01% TO 0.1% 8 10 12 14 16 18 20 22 24 26 28 30 32 SETTLING TIME (s)
1168 G19
Falling Edge Settling Time (0.10%)
VIN (V) VIN (V) 0 -5 -10 0.10 SETTLING (%) 0.05 0 VOUT (V) 0 -5 -10 5s/DIV t=0 TA = 25C VS = 15V RL = 2k CL = 15pF
1168 G29
0.10
VOUT (V)
Settling Time (0.01%) vs Load Capacitance
36 PEAK-TO-PEAK OUTPUT SWING (V) 34 32 SETTLING TIME (s) 30 28 G = 10, FALLING EDGE 26 24 22 20 18 10 G = 10, RISING EDGE VS = 15V TA = 25C RL = 1k STEP SIZE = 10V G = 1, FALLING EDGE G = 1, RISING EDGE G = 100, FALLING EDGE G = 100, RISING EDGE 35 30 25 20 15 10 5 0 30 100 300 LOAD CAPACITANCE (pF) 1000
1168 G26
UW
VOUT VOUT
Settling Time vs Gain
1000 VS = 15V TA = 25C VOUT = 10V TO 0.01%
34 32 30 28 26 24 22 20 18
Settling Time (0.1%) vs Load Capacitance
G = 1, FALLING EDGE G = 1, RISING EDGE G = 100, FALLING EDGE
G = 100, RISING EDGE VS = 15V TA = 25C RL = 1k STEP SIZE = 10V 10
G = 10, FALLING EDGE G = 10, RISING EDGE
10
1 1 10 GAIN
1168 G18
100
1000
16
30 100 300 LOAD CAPACITANCE (pF)
1000
1168 G25
Rising Edge Settling Time (O.10%)
10 5 0 0.10 SETTLING (%) 0.05 0 10 5 0 5s/DIV t=0 TA = 25C VS = 15V RL = 2k CL = 15pF
1168 G28
0.05
0.05 0.10
Undistorted Output Swing vs Frequency
G = 10, 100, 1000 VS = 15V TA = 25C
G=1
1
10 100 FREQUENCY (kHz)
1000
1168 G31
7
LT1168 TYPICAL PERFOR A CE CHARACTERISTICS
Output Voltage Swing vs Load Current
REFERRED TO SUPPLY VOLTAGE (SOURCE)
+ VS VS = 15V + VS - 0.5 + VS - 1.0 + VS - 1.5 + VS - 2.5 - VS + 2.5 - VS + 2.0 - VS + 1.5 - VS + 1.0 - VS + 0.5 - VS 0.01 1 10 0.1 OUTPUT CURRENT (mA) 100
1168 G20
OUTPUT VOLTAGE SWING (V) (SINK)
5V/DIV
+ VS - 2.0
G=1 VS = 15V RL = 2k CL = 60pF
50s/DIV
1168 G03
20mV/DIV
Large-Signal Transient Response
20mV/DIV
5V/DIV
G = 10 VS = 15V RL = 2k CL = 60pF
50s/DIV
1168 G05
G = 10 VS = 15V RL = 2k CL = 60pF
10s/DIV
1168 G06
5V/DIV
Small-Signal Transient Response
20mV/DIV
20mV/DIV
5V/DIV
G = 100 VS = 15V RL = 2k CL = 60pF
10s/DIV
8
UW
1168 G08
Large-Signal Transient Response
85C 25C - 40C
Small-Signal Transient Response
G=1 VS = 15V RL = 2k CL = 60pF
10s/DIV
1168 G04
Small-Signal Transient Response
Large-Signal Transient Response
G = 100 VS = 15V RL = 2k CL = 60pF
50s/DIV
1168 G07
Large-Signal Transient Response
Small-Signal Transient Response
G = 1000 VS = 15V RL = 2k CL = 60pF
200s/DIV
1168 G09
G = 1000 VS = 15V RL = 2k CL = 60pF
200s/DIV
1168 G10
LT1168 TYPICAL PERFOR A CE CHARACTERISTICS
Negative Power Supply Rejection Ratio vs Frequency
NEGATIVE POWR SUPPLY REJECTION RATIO (dB)
POSITIVE POWR SUPPLY REJECTION RATIO (dB)
160 G = 1000 140 120 100 80 60 40 20 0 0.1 V + = 15V TA = 25C 1 10 100 1k FREQUENCY (Hz) 10k 100k
1168 G21
G = 100 G = 10 G=1
140 120 100 80 60 40 20 0 0.1 1
COMMON MODE REJECTION RATIO (dB)
Warm-Up Drift
35
INPUT BIAS AND OFFSET CURRENT (pA)
CHANGE IN OFFSET VOLTAGE (V)
30 25 SO-8 20 15 N-8 10 5 0 0 1 2 3 4 TIME AFTER POWER-ON (MINUTES) 5
BLOCK DIAGRAM
-IN 2
V-
RG 1 RG 8 V+ VB
+
A2
R7 30k
R4 400 +IN 3 Q2
-
C2 V- R2 24.7k 7 4 PREAMP STAGE DIFFERENCE AMPLIFIER STAGE V+ V-
V-
Figure 1. Block Diagram
+
-
UW
R3 400
Positive Power Supply Rejection Ratio vs Frequency
160 G = 1000 G = 100 G = 10 G=1 160 140 120
Common Mode Rejection Ratio vs Frequency (1k Source Impedance)
G = 1000 G = 100 G = 10 100 G=1 80 60 40 20 0 VS = 15V TA = 25C 1k SOURCE IMBALANCE 0.1 1 10 100 1k FREQUENCY (Hz) 10k 100k
1168 G23
V - = -15V TA = 25C 10 100 1k FREQUENCY (Hz) 10k 100k
1168 G22
Input Bias and Offset Current vs Temperature
500 400 300 200 100 0 -100 -200 -300 -400 -500 -75 -50 -25 0 25 50 TEMPERATURE 75 100 125
1168 G30
VS = 15V VCM = 0V
IOS IB
1168 G24
W
V+
VB
+
A1
R5 30k
R6 30k 6 OUTPUT
-
C1 Q1 R1 24.7k
A3
V- R8 30k 5 REF
1168 F01
9
LT1168
THEORY OF OPERATIO
The LT1168 is a modified version of the three op amp instrumentation amplifier. Laser trimming and monolithic construction allow tight matching and tracking of circuit parameters over the specified temperature range. Refer to the block diagram (Figure 1) to understand the following circuit description. The collector currents in Q1 and Q2 are trimmed to minimize offset voltage drift, thus assuring a high level of performance. R1 and R2 are trimmed to an absolute value of 24.7k to assure that the gain can be set accurately (0.6% at G = 100) with only one external resistor RG. The value of RG in parallel with R1 (R2) determines the transconductance of the preamp stage. As RG is reduced for larger programmed gains, the transconductance of the input preamp stage increases to that of the input transistors Q1 and Q2. This increases the open-loop gain when the programmed gain is increased, reducing the input referred gain related errors and noise. The input voltage noise at gains greater than 50 is determined only by Q1 and Q2. At lower gains the noise of the difference amplifier and preamp gain setting resistors increase the noise. The gain bandwidth product is determined by C1, C2 and the preamp transconductance which increases with programmed gain. Therefore, the bandwidth does not drop proportionally with gain. The input transistors Q1 and Q2 offer excellent matching, which is inherent in NPN bipolar transistors, as well as picoampere input bias current due to superbeta processing. The collector currents in Q1 and Q2 are held constant due to the feedback through the Q1-A1-R1 loop and Q2-A2-R2 loop which in turn impresses the differential input voltage across the external gain set resistor RG. Since the current that flows through RG also flows through R1 and R2, the ratios provide a gained-up differential voltage,G = (R1 + R2)/RG, to the unity-gain difference amplifier A3. The common mode voltage is removed by A3, resulting in a single-ended output voltage referenced to the voltage on the REF pin. The resulting gain equation is: G = (49.4k / RG) + 1 solving for the gain set resistor gives: RG = 49.4k /(G - 1) Table 1 shows appropriate 1% resistor values for a variety of gains.
10
U
Table 1
DESIRED GAIN 1 2 5 10 20 50 100 200 500 1000 RG Open 49400 12350 5488.89 2600 1008.16 498.99 248.24 99 49.95 CLOSEST 1% VALUE Open 49900 12400 5490 2610 1000 499 249 100 49.4 RESULTANT GAIN 1 1.99 4.984 9.998 19.927 50.4 99.998 199.394 495 1001
Input and Output Offset Voltage The offset voltage of the LT1168 has two components: the output offset and the input offset. The total offset voltage referred to the input (RTI) is found by dividing the output offset by the programmed gain (G) and adding it to the input offset. At high gains the input offset voltage dominates, whereas at low gains the output offset voltage dominates. The total offset voltage is: Total input offset voltage (RTI) = input offset + (output offset/G) Total output offset voltage (RTO) = (input offset * G) + output offset Reference Terminal The reference terminal is one end of one of the four 30k resistors around the difference amplifier. The output voltage of the LT1168 (Pin 6) is referenced to the voltage on the reference terminal (Pin 5). Resistance in series with the REF pin must be minimized for best common mode rejection. For example, a 6 resistance from the REF pin to ground will not only increase the gain error by 0.02% but will lower the CMRR to 80dB. Single Supply Operation For single supply operation, the REF pin can be at the same potential as the negative supply (Pin 4) provided the output of the instrumentation amplifier remains inside the specified operating range and that one of the inputs is at least 2.5V above ground. The barometer application later
LT1168
THEORY OF OPERATIO
in this data sheet is an example that satisfies these conditions. The resistance Rb from the bridge transducer to ground sets the operating current for the bridge and also has the effect of raising the input common mode voltage. The output of the LT1168 is always inside the specified range since the barometric pressure rarely goes low enough to cause the output to rail (30.00 inches of Hg corresponds to 3.000V). For applications that require the output to swing at or below the REF potential, the voltage on the REF pin can be level shifted. An op amp is used to buffer the voltage on the REF pin since a parasitic series resistance will degrade the CMRR. The application in the front of this data sheet, Single Supply Pressure Monitor, is an example. Output Offset Trimming The LT1168 is laser trimmed for low offset voltage so that no external offset trimming is required for most applications. In the event that the offset needs to be adjusted, the circuit in Figure 2 is an example of an optional offset adjust circuit. The op amp buffer provides a low impedance to the REF pin where resistance must be kept to minimum for best CMRR and lowest gain error. Input Bias Current Return Path The low input bias current of the LT1168 (250pA) and the high input impedance (200G) allow the use of high impedance sources without introducing additional offset voltage errors, even when the full common mode range is
-IN
1
RG 8 +IN
LT1112
Figure 2. Optional Trimming of Output Offset Voltage
THERMOCOUPLE
LT1168
MICROPHONE, HYDROPHONE, ETC
LT1168
10k
200k
200k CENTER-TAP PROVIDES BIAS CURRENT RETURN
1168 F03
Figure 3. Providing an Input Common Mode Current Path
-
+
+
10mV ADJUSTMENT RANGE
-
+
3
-
-
+
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required. However, a path must be provided for the input bias currents of both inputs when a purely differential signal is being amplified. Without this path the inputs will float to either rail and exceed the input common mode range of the LT1168, resulting in a saturated input stage. Figure 3 shows three examples of an input bias current path. The first example is of a purely differential signal source with a 10k input current path to ground. Since the impedance of the signal source is low, only one resistor is needed. Two matching resistors are needed for higher impedance signal sources as shown in the second example. Balancing the input impedance improves both common mode rejection and DC offset.
2 LT1168 REF 5 10mV 100 10k 100 -10mV 6 OUTPUT V+ V-
1168 F02
- +
LT1167 LT1168
11
LT1168
APPLICATIONS INFORMATION
The LT1168 is a low power precision instrumentation amplifier that requires only one external resistor to accurately set the gain anywhere from 1 to 1000. The LT1168 is trimmed for critical DC parameters such as gain error (0.04%, G = 10), input offset voltage (40V, RTI), CMRR (90dB min, G = 1) and PSRR (103dB min, G = 1). These trims allow the amplifier to achieve very high DC accuracy. The LT1168 achieves low input bias current of just 250pA (max) through the use of superbeta processing. The output can handle capacitive loads up to 1000pF in any gain configuration and the inputs are protected against ESD strikes up to 13kV (human body). Input Protection The LT1168 can safely handle up to 20mA of input current in an overload condition. Adding an external 5k input resistor in series with each input allows DC input fault voltage up to 100V and improves the ESD immunity to 8kV (contact) and 15kV (air discharge), which is the IEC 1000-4-2 level 4 specification. If lower value input resistors must be used, a clamp diode from the positive supply to each input will maintain the IEC 1000-4-2 specification to level 4 for both air and contact discharge. A 2N4393 drain/source to gate is a good low leakage diode for use with 1k resistors, see Figure 4. The input resistors should be carbon and not metal film or carbon film.
J1 2N4393 RIN J2 2N4393 OPTIONAL FOR RIN < 20k VCC
RG RIN
LT1168
REF
VEE
Figure 4. Input Protection
RFI Reduction In many industrial and data acquisition applications, instrumentation amplifiers are used to accurately amplify small signals in the presence of large common mode voltages or high levels of noise. Typically, the sources of
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these very small signals (on the order of microvolts or millivolts) are sensors that can be a significant distance from the signal conditioning circuit. Although these sensors may be connected to signal conditioning circuitry, using shielded or unshielded twisted-pair cabling, the cabling may act as antennae, conveying very high frequency interference directly into the input stage of the LT1168. The amplitude and frequency of the interference can have an adverse effect on an instrumentation amplifier's input stage by causing an unwanted DC shift in the amplifier's input offset voltage. This well known effect is called RFI rectification and is produced when out-of-band interference is coupled (inductively, capacitively or via radiation) and rectified by the instrumentation amplifier's input transistors. These transistors act as high frequency signal detectors, in the same way diodes were used as RF envelope detectors in early radio designs. Regardless of the type of interference or the method by which it is coupled into the circuit, an out-of-band error signal appears in series with the instrumentation amplifier's inputs. To significantly reduce the effect of these out-of-band signals on the input offset voltage of instrumentation amplifiers, simple lowpass filters can be used at the inputs. This filter should be located very close to the input pins of the circuit. An effective filter configuration is illustrated in Figure 5, where three capacitors have been added to the inputs of the LT1168. Capacitors CXCM1 and CXCM2 form lowpass filters with the external series resistors RS1, 2 to any out-of-band signal appearing on each of the input traces. Capacitor CXD forms a filter to reduce any unwanted signal that would appear across the input traces. An added benefit to using CXD is that the circuit's AC common mode rejection is not degraded due to common mode capacitive imbalance. The differential mode and common mode time constants associated with the capacitors are: tDM(LPF) = (2)(RS)(CXD) tCM(LPF) = (RS1, 2)(CXCM1, 2) Setting the time constants requires a knowledge of the frequency, or frequencies of the interference. Once this frequency is known, the common mode time constants can be set followed by the differential mode time constant.
OUT
1168 F04
LT1168
APPLICATIONS INFORMATION
To avoid any possibility of inadvertently affecting the signal to be processed, set the common mode time constant an order of magnitude (or more) larger than the differential mode time constant. Set the common mode time constants such that they do not degrade the LT1168 inherent AC CMR. Then the differential mode time constant can be set for the bandwidth required for the application. Setting the differential mode time constant close to the sensor's BW also minimizes any noise pickup along the leads. To avoid any possibility of common mode to differential mode signal conversion, match the common mode time constants to 1% or better. If the sensor is an RTD or a resistive strain gauge, then the series resistors RS1, 2 can be omitted, if the sensor is in proximity to the instrumentation amplifier.
RS1 CXCM1 1.6k 0.001F V+
CXD 0.1F RS2 1.6k CXCM2 0.001F EXTERNAL RFI FILTER
RG
Figure 5. Adding a Simple RC Filter at the Inputs to an Instrumentation Amplifier is Effective in Reducing Rectification of High Frequency Out-of-Band Signals
PATIENT/CIRCUIT PROTECTION/ISOLATION +IN C1 0.01F R2 1M R1 12k R3 30k R4 30k 2
PATIENT GND
1
1/2 LT1112
-IN
-
IN -
+
IN +
LT1168
V- f- 3dB 500Hz
1168 F05
RG 6k 1 2
3 AV = 101 POLE AT 1kHz
Figure 6. Nerve Impulse Amplifier
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Nerve Impulse Amplifier The LT1168's low current noise makes it ideal for EMG monitors that have high source impedances. Demonstrating the LT1168's ability to amplify low level signals, the circuit in Figure 6 takes advantage of the amplifier's high gain and low noise operation. This circuit amplifies the low level nerve impulse signals received from a patient at Pins 2 and 3. RG and the parallel combination of R3 and R4 set a gain of ten. The potential on LT1112's Pin 1 creates a ground for the common mode signal. C1 was chosen to maintain the stability of the patient ground. The LT1168's high CMRR ensures that the desired differential signal is amplified and unwanted common mode signals are attenuated. Since the DC portion of the signal is not important, R6 and C2 make up a 0.3Hz highpass filter. The AC signal at LT1112's Pin 5 is amplified by a gain of 101 set by R7/R8 +1. The parallel combination of C3 and R7 form a lowpass filter that decreases this gain at frequencies above 1kHz. The ability to operate at 3V on 350A of supply current makes the LT1168 ideal for battery-powered applications. Total supply current for this application is 1.05mA. Proper safeguards, such as isolation, must be added to this circuit to protect the patient from possible harm.
VOUT
3V
+
7 C2 0.47F LT1168 G = 10 5 6
0.3Hz HIGHPASS 3V 5 R6 1M
+ -
8 1/2 LT1112 4 -3V 7 OUTPUT 1V/mV
6
-
4 -3V R8 100
R7 10k
C3 15nF
1168 F06
13
LT1168
APPLICATIONS INFORMATION
Low IB Favors High Impedance Bridges, Lowers Dissipation The LT1168's low supply current, low supply voltage operation and low input bias currents allow it to fit nicely into battery-powered applications. Low overall power dissipation necessitates using higher impedance bridges. The single supply pressure monitor application, Figure 7, shows the LT1168 connected to the differential output of a 3.5k bridge. The picoampere input bias currents keep the error caused by offset current to a negligible level. The LT1112 level shifts the LT1168's reference pin and the ADC's analog ground pins above ground. The LT1168's and LT1112's combined power dissipation is still less than the bridge's. This circuit's total supply current is just 2.2mA.
5V
1 3.5k 3.5k G = 200 249 3.5k 3.5k
3 8
+
LT1168 1 2 5
-
4
Figure 7. Single Supply Pressure Monitor
TYPICAL APPLICATIONS
Single Supply Barometer
VS R5 392k 2 LT1634CCZ-1.25 1 2 LUCAS NOVA SENOR NPC-1220-015-A-3L 1 4 5k R6 1k 5k R1 825 2 6 R4 50k R3 50k 6 R8 100k RSET 5 5k 5k R2 12 8 3 LT1168 G = 60 5 4 TO 4-DIGIT DVM 6
3
1/2 LT1490
-
4
+
1/2 LT1490 7 R7 50k
5
-
0.6% ACCURACY AT 25C 1.7% ACCURACY AT 0C TO 60C VS = 8V TO 30V
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+
+
3
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+
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BI TECHNOLOGIES 67-8-3 R40KQ (0.02% RATIO MATCH)
40k 7 REF 6 20k IN ADC LTC(R)1286 AGND DIGITAL DATA OUTPUT
+
40k 1/2 LT1112
-
1168 TA05
VS 1 2 1 7
-
VOLTS 2.800 3.000 3.200
INCHES Hg 28.00 30.00 32.00
1168 TA03
LT1168
TYPICAL APPLICATIONS
AC Coupled Instrumentation Amplifier
-IN 2 1
+IN
1
1/2 LT1124
9V R8 392k 2 LT1634CCZ-1.25 1 2
4-Digit Pressure Sensor
LUCAS NOVA SENOR NPC-1220-015A-3L 1 4 5k R9 1k 5k
3
+ -
4
1/4 LT1114 11
-
1 R1 825 R2 12
2 6
5k
5k
RSET 5
+
3
0.6% ACCURACY AT ROOM TEMP 1.7% ACCURACY AT 0C TO 60C VOLTS 2.800 3.000 3.200 INCHES Hg 28.00 30.00 32.00
PACKAGE DESCRIPTIO
Dimensions in inches (millimeters) unless otherwise noted. N8 Package 8-Lead PDIP (Narrow 0.300)
(LTC DWG # 05-08-1510)
0.300 - 0.325 (7.620 - 8.255)
0.045 - 0.065 (1.143 - 1.651)
0.009 - 0.015 (0.229 - 0.381)
0.065 (1.651) TYP 0.125 (3.175) 0.020 MIN (0.508) MIN 0.018 0.003 (0.457 0.076)
(
+0.035 0.325 -0.015 +0.889 8.255 -0.381
)
0.100 (2.54) BSC
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
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LT1168 6 C1 0.1F R1 1M
RG 8 3
OUTPUT
REF
+
5
2 f -3dB = 1 (2)(R1)(C1)
1168 TA02
3
= 1.59Hz
9V 2 1 LT1168 G = 60 8 3 5
-
7 6
+
4
10
+
1/4 LT1114 8
TO 4-DIGIT DVM
9 12
+
1/4 LT1114 14
-
R6 50k R7 180k
13
-
R4 100k
R5 100k
R3 51k
C1 1F
1168 TA04
0.130 0.005 (3.302 0.127)
0.400* (10.160) MAX 8 7 6 5
0.255 0.015* (6.477 0.381)
1
2
3
4
N8 1098
15
LT1168
TYPICAL APPLICATIO U
R2 4k P1 3 14 1 16 LTC201 2 +15V 8 1 2 15 12 13 4 5 7 10 P2 8 9 6 11 R1 4k GAIN SET 3 8 1 2
Programmable Audio HPF/LPF with "Pop-Less" Switching
+15V 7 LT1168 6 5 4 -15V HPF
+ -
R3 8k
C1 100F 5
+
1/2 LT1462 7 LPF P1 P2 POLE -- 0 100 0 1 1 1 0 < 0.8V 1 > 2.4V Hz
1168 TA06
- +
6
1/2 LT1462 VIN 3 4 -15V
NC +15V -15V TOTAL SUPPLY CURRENT < 400A
-
200 400
PACKAGE DESCRIPTIO
0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0- 8 TYP
0.053 - 0.069 (1.346 - 1.752)
0.014 - 0.019 (0.355 - 0.483) TYP *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
0.016 - 0.050 (0.406 - 1.270)
RELATED PARTS
PART NUMBER LTC1100 LT1101 LT1102 LT1167 DESCRIPTION Precision Chopper-Stabilized Instrumentation Amplifier Precision, Micropower, Single Supply Instrumentation Amplifier High Speed, JFET Instrumentation Amplifier Single Resistor Programmable Precision Instrumentation Amplifier COMMENTS G = 10 or 100, VOS = 10V, IB = 50pA G = 10 or 100, IS = 105A G = 10 or 100, Slew Rate = 30V/s Lower Noise than LT1168, eN = 7.5nV/Hz
16
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 q FAX: (408) 434-0507 q www.linear-tech.com
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Dimensions in inches (millimeters) unless otherwise noted. S8 Package 8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 - 0.197* (4.801 - 5.004) 8 0.004 - 0.010 (0.101 - 0.254) 0.228 - 0.244 (5.791 - 6.197) 0.150 - 0.157** (3.810 - 3.988) 7 6 5
0.050 (1.270) BSC
1
2
3
4
SO8 1298
1168i LT/TP 0300 4K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1998

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