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LT1789-1 Micropower, Single Supply Rail-to-Rail Output Instrumentation Amplifier
FEATURES
s s s s s s s s s s s s s s
DESCRIPTIO
Micropower: 95A Max Supply Current Low Input Offset Voltage: 100V Max Low Input Offset Voltage Drift: 0.5V/C Max Single Gain Set Resistor: G = 1 to 1000 Inputs Common Mode to V - Wide Supply Range: 2.2V to 36V Total Supply CMRR: G = 10, 96dB Min Gain Error: G = 10, 0.25% Max Gain Nonlinearity: G = 10, 40ppm Max Input Bias Current: 40nA Max PSRR: G = 10, 100dB Min Rail-to-Rail Output 100Hz Voltage Noise: 48nV/Hz 0.1Hz to 10Hz Noise: 1.5VP-P
APPLICATIO S
s s s s s s
Portable Instrumentation Bridge Amplifiers Strain Gauge Amplifiers Thermocouple Amplifiers Differential to Single-Ended Converters Medical Instrumentation
The LT (R)1789-1 is a micropower, precision instrumentation amplifier that is optimized for low voltage single supply operation, with a quiescent current of 95A max for 2.2V to 36V supplies, inputs that common mode to ground and an output that swings within 100mV of ground. The LT1789-1 requires only one external resistor to set gains of 1 to 1000. The high accuracy of the LT1789-1 (40ppm maximum nonlinearity and 0.25% max gain error) is unmatched by other micropower instrumentation amplifiers. The LT1789-1 is laser trimmed for very low input offset voltage (100V max), drift (0.5V/C), high CMRR (96dB, G = 10) and PSRR (100dB, G = 10). The output can handle capacitive loads up to 400pF in any gain configuration while the inputs are ESD protected up to 10kV (human body model). The LT1789-1 is offered in the 8-pin SO package, requiring significantly less PC board area than discrete multi op amp and resistor designs. The LT1789-1 is the best choice for circuits requiring precision, micropower and low supply voltage operation.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
0.5A to 4A Voltage Controlled Current Source
C1 4700pF VS
VIN R2 10k
ILOAD =
VS = 3.3V TO 32V VIN RSENSE * 10 = 1A PER VOLT AS SHOWN
RISE TIME 250s, 10% TO 90%, 1A TO 2A OUTPUT STEP INTO 0.25 LOAD
+
3
-
R1 90.9k
VS 2 7 LT1636 5 4 R4 10k C2 3300pF 6
C3 0.1F R3 100 VS 7 6
8k
120 TIP127*
+
3 8
3 1 2 4
REF LT1789-1 1 5 4
-
2
U
* ENSURE ADEQUATE POWER DISSIPATION CAPABILITY AT HIGHER VOLTAGES, CURRENTS AND DUTY CYCLES RSENSE* 0.1 ILOAD RLOAD*
1789 TA03
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LT1789-1
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW RG 1 -IN 2 +IN 3 -VS 4 8 RG 7 +VS 6 OUT 5 REF
Supply Voltage (V+ to V-) ........................................ 36V Differential Input Voltage ......................................... 36V Input Current (Note 3) ........................................ 20mA Output Short-Circuit Duration .......................... Indefinite Operating Temperature Range ................ - 40C to 85C Specified Temperature Range (Note 4) LT1789C-1 (Note 4) ........................... - 40C to 85C LT1789I-1 .......................................... - 40C to 85C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
ORDER PART NUMBER LT1789CS8-1 LT1789IS8-1 S8 PART MARKING 17891 1789I1
S8 PACKAGE 8-LEAD PLASTIC SO
TJMAX = 150C, JA = 190C/ W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
VS = 3V, 0V; VS = 5V, 0V; R L = 20k, VCM = VREF = half supply, TA = 25C, unless otherwise noted.
SYMBOL PARAMETER G Gain Range Gain Error (Note 6) CONDITIONS G = 1 + (200k/RG) G = 1, VO = (- VS) + 0.1V to (+VS) - 1V G = 10, VO = (- VS) + 0.1V to (+VS) - 0.3V (Note 2) G = 100, VO = (- VS) + 0.1V to (+VS) - 0.3V (Note 2) G = 1000, VO = (- VS) + 0.1V to (+VS) - 0.3V (Note 2) G = 1, VO = (-VS) + 0.1V to (+VS) - 1V G = 10, VO = (-VS) + 0.1V to (+VS) - 0.3V G = 100, VO = (-VS) + 0.1V to (+VS) - 0.3V G = 1000, VO = (-VS) + 0.1V to (+VS) - 0.3V VOST = VOSI + VOSO/G G = 1000 G=1 (Note 6) (Note 6) G = 1, fO = 0.1Hz to 10Hz G = 10 G = 100, 1000 fO = 100Hz (Note 7) fO = 100Hz fO = 0.1Hz to 10Hz fO = 100Hz VIN = 0V to (+VS) - 1V (Note 6) Differential Common Mode G = 1, Other Input Grounded 1k Source Imbalance, VCM = 0V to (+VS) - 1V (Note 6) G=1 G = 10 G = 100, 1000 0 79 96 100 88 106 114 0.75 15 150 0.2 19 5.0 1.5 1.0 48 330 16 100 1.6 20 17 (+VS) - 1 85 100 750 4 40 V V nA nA VP-P VP-P VP-P nV/Hz nV/Hz pAP-P fA/Hz G pF pF V dB dB dB MIN 1 0.02 0.06 0.06 0.13 35 12 18 90 TYP MAX 1000 0.20 0.25 0.27 100 40 75 % % % % ppm ppm ppm ppm UNITS
Gain Nonlinearity (Note 6)
VOST VOSI VOSO IOS IB en
Total Input Referred Offset Voltage Input Offset Voltage Output Offset Voltage Input Offset Current Input Bias Current Input Noise Voltage, RTI (Referred to Input)
Total RTI Noise = eni2 + (eno/G)2 eni eno in RIN CIN VCM CMRR Input Noise Voltage Density, RTI Output Noise Voltage Density, RTI Input Noise Current Input Noise Current Density Input Resistance Input Capacitance Input Voltage Range Common Mode Rejection Ratio
2
U
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WW
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LT1789-1
ELECTRICAL CHARACTERISTICS
VS = 3V, 0V; VS = 5V, 0V; R L = 20k, VCM = VREF = half supply, TA = 25C, unless otherwise noted.
SYMBOL PARAMETER PSRR Power Supply Rejection Ratio CONDITIONS VS = 2.5V to 12.5V, VCM = VREF = 1V G=1 G = 10 G = 100, 1000 (Note 7) MIN 90 100 102 TYP 100 113 116 2.2 67 54 (+VS) - 0.3 (+VS) - 0.19 Short to GND Short to +VS G=1 G = 10 G = 100 G = 1000 G = 1, VOUT = 0.1V to 2.1V 4V Step, G = 1, VS = 5V 1.9 7.6 60 30 3 0.2 0.021 260 220 2.7 1 0.0001 2.5 95 100 MAX UNITS dB dB dB V A mV V mA mA kHz kHz kHz kHz V/s s k A
Minimum Supply Voltage IS VOL VOH ISC BW Supply Current Output Voltage Swing LOW Output Voltage Swing HIGH Short-Circuit Current Bandwidth
SR RREFIN IREFIN AVREF
Slew Rate Settling Time to 0.01% Reference Input Resistance Reference Input Current Reference Gain to Output
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LT1789-1
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER Gain Error (Note 6) CONDITIONS
The q denotes the specifications which apply over the temperature range of 0C TA 70C. VS = 3V, 0V; VS = 5V, 0V; R L = 20k, VCM = VREF = half supply, unless otherwise noted. (Note 4)
MIN
q q q q q q q
TYP
MAX 0.25 0.30 0.32 185 90 120
UNITS % % % ppm ppm ppm ppm/C V V V V V/C V/C nA pA/C nA pA/C V dB dB dB dB dB dB
G = 1, VO = (-VS) + 0.3V to (+VS) - 1V G = 10, VO = (-VS) + 0.3V to (+VS) - 0.5V (Note 2) G = 100, VO = (-VS) + 0.3V to (+VS) - 0.5V (Note 2) G = 1, VO = (-VS) + 0.3V to (+VS) - 1V G = 10, VO = (-VS) + 0.3V to (+VS) - 0.5V G = 100, VO = (-VS) + 0.3V to (+VS) - 0.5V G < 1000 (Notes 2, 3) G = 1000 (Notes 3, 5) G=1 (Notes 3, 5) (Note 3) (Note 3) (Note 6) (Note 6) G = 1, Other Input Grounded
Gain Nonlinearity (Note 6)
G/T VOST VOSI VOSIH VOSO VOSOH VOSI/T VOSO/T IOS IOS/T IB IB/T VCM CMRR
Gain vs Temperature Input Offset Voltage Input Offset Voltage Hysteresis Output Offset Voltage Output Offset Voltage Hysteresis Input Offset Voltage Drift (RTI) Output Offset Voltage Drift Input Offset Current Input Offset Current Drift Input Bias Current Input Bias Current Drift Input Voltage Range Common Mode Rejection Ratio
5
50 150
Total Input Referred Offset Voltage VOST = VOSI + VOSO/G
q q q q q q q q q q q
3 50 0.2 1.5 3
10 950 100 0.5 4 4.5 45
50 0.2 77 94 98 88 98 100 2.5 115 110 (+VS) - 0.38 (+VS) - 1
1k Source Imbalance, VCM = 0.2V to (+VS) - 1V (Note 6) G=1 q G = 10 q G = 100, 1000 q VS = 2.5V to 12.5V, VCM = VREF = 1V G=1 G = 10 G = 100, 1000 (Note 7)
q q q q q q q
PSRR
Power Supply Rejection Ratio
Minimum Supply Voltage IS VOL VOH Supply Current Output Voltage Swing LOW Output Voltage Swing HIGH
V A mV V
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LT1789-1
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER Gain Error (Note 6) CONDITIONS
The q denotes the specifications which apply over the temperature range of -40C TA 85C. VS = 3V, 0V; VS = 5V, 0V; R L = 20k, VCM = VREF = half supply, unless otherwise noted. (Note 4)
MIN
q q q q q q q
TYP
MAX 0.30 0.35 0.37 250 105 160
UNITS % % % ppm ppm ppm ppm/C V V V V V/C V/C nA pA/C nA pA/C V dB dB dB dB dB dB
G = 1, VO = (-VS) + 0.3V to (+VS) - 1V G = 10, VO = (-VS) + 0.3V to (+VS) - 0.5V (Note 2) G = 100, VO = (-VS) + 0.3V to (+VS) - 0.5V (Note 2) G = 1, VO = (-VS) + 0.3V to (+VS) - 1V G = 10, VO = (-VS) + 0.3V to (+VS) - 0.5V G = 100, VO = (-VS) + 0.3V to (+VS) - 0.5V G < 1000 (Notes 2, 3) G = 1000 (Notes 3, 5) G=1 (Notes 3, 5) (Note 3) (Note 3) (Note 6) (Note 6) G = 1, Other Input Grounded
Gain Nonlinearity (Note 6)
G/T VOST VOSI VOSIH VOSO VOSOH VOSI/T VOSO/T IOS IOS/T IB IB/T VCM CMRR
Gain vs Temperature Input Offset Voltage Input Offset Voltage Hysteresis Output Offset Voltage Output Offset Voltage Hysteresis Input Offset Voltage Drift (RTI) Output Offset Voltage Drift Input Offset Current Input Offset Current Drift Input Bias Current Input Bias Current Drift Input Voltage Range Common Mode Rejection Ratio
5
50 175
Total Input Referred Offset Voltage VOST = VOSI + VOSO/G
q q q q q q q q q q q
3 50 0.2 1.5 3
10 1050 100 0.5 4 5 50
50 0.2 75 92 96 86 96 98 2.5 125 120 (+VS) - 0.40 (+VS) - 1
1k Source Imbalance, VCM = 0.2V to (+VS) - 1V (Note 6) G=1 q G = 10 q G = 100, 1000 q VS = 2.5V to 12.5V, VCM = VREF = 1V G=1 G = 10 G = 100, 1000 (Note 7)
q q q q q q q
PSRR
Power Supply Rejection Ratio
Minimum Supply Voltage IS VOL VOH Supply Current Output Voltage Swing LOW Output Voltage Swing HIGH
V A mV V
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ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER G Gain Range Gain Error
VS = 15V, R L = 20k, VCM = VREF = 0V, TA = 25C, unless otherwise noted.
CONDITIONS G = 1 + (200k/RG) VO = 10V G=1 G = 10 (Note 2) G = 100 (Note 2) G = 1000 (Note 2) VO = 10V G=1 G = 10 G = 100 G = 1000 VOST = VOSI + VOSO/G G = 1000 G=1 30 200 0.2 17 fO = 0.1Hz to 10Hz G=1 G = 10 G = 100, 1000 fO = 100Hz fO = 100Hz fO = 0.1Hz to 10Hz fO = 100Hz 2 Differential Common Mode G = 1, Other Input Grounded 1k Source Imbalance, VCM = -15V to 14V G=1 G = 10 G = 100, 1000 VS = 1.25V to 16V G=1 G = 10 G = 100, 1000 -15 80 98 102 94 104 106 89 108 117 107 118 121 1.25 85 14.5 Short to - VS Short to + VS 14.7 2.2 8.5 130 5.0 1.5 1.0 49 330 19 100 4.7 20 17 14 80 235 1 4 40 V mV nA nA VP-P VP-P VP-P nV/Hz nV/Hz pAP-P fA/Hz G pF pF V dB dB dB dB dB dB V A V mA mA MIN 1 0.01 0.04 0.04 0.07 8 1 6 20 TYP MAX 1000 0.10 0.15 0.15 0.20 20 10 20 100 % % % % ppm ppm ppm ppm UNITS
Gain Nonlinearity
VOST VOSI VOSO IOS IB en
Total Input Referred Offset Voltage Input Offset Voltage Output Offset Voltage Input Offset Current Input Bias Current Input Noise Voltage, RTI
Total RTI Noise = eni2 + (eno/G)2 eni eno in RIN CIN VCM CMRR Input Noise Voltage Density, RTI Output Noise Voltage Density, RTI Input Noise Current Input Noise Current Density Input Resistance Input Capacitance Input Voltage Range Common Mode Rejection Ratio
PSRR
Power Supply Rejection Ratio
Minimum Supply Voltage IS VO ISC Supply Current Output Voltage Swing Short-Circuit Current
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ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER BW Bandwidth G=1 G = 10 G = 100 G = 1000
VS = 15V, R L = 20k, VCM = VREF = 0V, TA = 25C, unless otherwise noted.
CONDITIONS MIN TYP 60 30 3 0.2 0.012 0.026 460 220 VREF = 0 2.7 1 0.0001 MAX UNITS kHz kHz kHz kHz V/s s k A
SR RREFIN IREFIN AVREF
Slew Rate Settling Time to 0.01% Reference Input Resistance Reference Input Current Reference Gain to Output
G = 1, VOUT = 10V 10V Step, G = 1
The q denotes the specifications which apply over the temperature range of 0C TA 70C. VS = 15V, R L = 20k, VCM = VREF = 0V, unless otherwise noted. (Note 4)
SYMBOL PARAMETER Gain Error CONDITIONS VO = 10V G=1 G = 10 (Note 2) G = 100 (Note 2) G = 1000 (Note 2) VO = 10V G=1 G = 10 G = 100 G = 1000 G < 1000 (Notes 2, 3) VOST = VOSI + VOSO/G G = 1000 (Notes 3, 5) G=1 (Notes 3, 5) (Note 3) (Note 3)
q q q q q q q q q q q q q q q q q q q
MIN
TYP
MAX 0.15 0.20 0.20 0.30 25 15 25 120
UNITS % % % % ppm ppm ppm ppm ppm/C V V mV V V/C V/C nA pA/C nA pA/C V dB dB dB
Gain Nonlinearity
G/T VOST VOSI VOSIH VOSO VOSOH VOSI/T VOSO/T IOS IOS/T IB IB/T VCM CMRR
Gain vs Temperature Total Input Referred Offset Voltage Input Offset Voltage Input Offset Voltage Hysteresis Output Offset Voltage Output Offset Voltage Hysteresis Input Offset Voltage Drift (RTI) Output Offset Voltage Drift Input Offset Current Input Offset Current Drift Input Bias Current Input Bias Current Drift Input Voltage Range Common Mode Rejection Ratio
5
50 285
8 50 0.2 1.5 2
30 1.2 120 0.7 5 4.5 45
35 -14.8 78 96 100 14
G = 1, Other Input Grounded 1k Source Imbalance, VCM = -14.8V to 14V G=1 G = 10 G = 100, 1000
q q q q
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ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER PSRR Power Supply Rejection Ratio
The q denotes the specifications which apply over the temperature range of 0C TA 70C. VS = 15V, R L = 20k, VCM = VREF = 0V, unless otherwise noted. (Note 4)
CONDITIONS VS = 1.25V to 16V G=1 G = 10 G = 100, 1000
q q q q q q
MIN 92 102 104
TYP
MAX
UNITS dB dB dB
Minimum Supply Voltage IS VO SR Supply Current Output Voltage Swing Slew Rate G = 1, VOUT = 10V
1.25 150 14.25 0.010
V A V V/s
q
The q denotes the specifications which apply over the temperature range of -40C TA 85C. VS = 15V, R L = 20k, VCM = VREF = 0V, unless otherwise noted. (Note 4)
SYMBOL PARAMETER Gain Error CONDITIONS VO = 10V G=1 G = 10 (Note 2) G = 100 (Note 2) G = 1000 (Note 2) VO = 10V G=1 G = 10 G = 100 G = 1000 G < 1000 (Notes 2, 3) VOST = VOSI + VOSO/G G = 1000 (Notes 3, 5) G=1 (Notes 3, 5) (Note 3) (Note 3)
q q q q q q q q q q q q q q q q q q q
MIN
TYP
MAX 0.20 0.25 0.25 0.40 30 20 30 130
UNITS % % % % ppm ppm ppm ppm ppm/C V V mV V V/C V/C nA pA/C nA pA/C V dB dB dB
Gain Nonlinearity
G/T VOST VOSI VOSIH VOSO VOSOH VOSI/T VOSO/T IOS IOS/T IB IB/T VCM CMRR
Gain vs Temperature Total Input Referred Offset Voltage Input Offset Voltage Input Offset Voltage Hysteresis Output Offset Voltage Output Offset Voltage Hysteresis Input Offset Voltage Drift (RTI) Output Offset Voltage Drift Input Offset Current Input Offset Current Drift Input Bias Current Input Bias Current Drift Input Voltage Range Common Mode Rejection Ratio
5
50 305
8 50 0.2 1.5 2
30 1.3 120 0.7 5 5 50
35 -14.8 76 94 98 (+VS) - 1
G = 1, Other Input Grounded 1k Source Imbalance, VCM = -14.8V to 14V G=1 G = 10 G = 100, 1000
q q q q
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ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER PSRR Power Supply Rejection Ratio
The q denotes the specifications which apply over the temperature range of -40C TA 85C. VS = 15V, R L = 20k, VCM = VREF = 0V, unless otherwise noted. (Note 4)
CONDITIONS VS = 1.25V to 16V G=1 G = 10 G = 100, 1000
q q q q q q
MIN 90 100 102 1.25
TYP
MAX
UNITS dB dB dB V
Minimum Supply Voltage IS VO SR Supply Current Output Voltage Swing Slew Rate G = 1, VOUT = 10V
160 14.15 0.008
A V V/s
q
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: Does not include the effect of the external gain resistor RG. Note 3: This parameter is not 100% tested. Note 4: The LT1789C-1 is guaranteed to meet specified performance from 0C to 70C and is designed, characterized and expected to meet these extended temperature limits, but is not tested at -40C and 85C. The LT1789I-1 is guaranteed to meet the extended temperature limits.
Note 5: 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. Note 6: VS = 5V limits are guaranteed by correlation to VS = 3V and VS = 15V tests. Note 7: VS = 3V limits are guaranteed by correlation to VS = 5V and VS = 15V tests.
TYPICAL PERFOR A CE CHARACTERISTICS
Supply Current vs Supply Voltage
120 110
SUPPLY CURRENT (A)
125C
INPUT BIAS CURRENT (nA)
INPUT BIAS CURRENT (nA)
100 90 80 70 60 50 40 30 20 0
25C -55C
5
10 15 20 25 30 35 TOTAL SUPPLY VOLTAGE (V)
UW
1789 G01
Input Bias Current vs Temperature
0 VS = 5V, 0V VREF = 2.5V -10 -12 -14 -16 -18 -20 -22 -24 -26 -28
40
Input Bias Current vs Common Mode Input Voltage
-55C
-5
125C 25C 85C
-10
-15
-20
-25 -50 -25
VS = 5V, 0V VREF = 2.5V
50 25 0 75 TEMPERATURE (C)
100
125
-30 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 COMMON MODE INPUT VOLTAGE (V)
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LT1789-1 TYPICAL PERFOR A CE CHARACTERISTICS
Output Voltage Swing vs Load Current
5.0
OUTPUT VOLTAGE SWING--SOURCING (V)
4.8 4.6 4.4 4.2 4.0 VS = 5V, 0V VREF = 2.5V 125C 25C 125C SOURCE 25C 1.6 1.4 1.2 1.0 0.8 0.6 0.4 SINK -55C 0.2 0 0.001 0.1 1 0.01 OUTPUT CURRENT (mA) 10
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GAIN (dB)
40 30 20 10 0 -10
G = 100
SLEW RATE (V/s)
Common Mode Rejection Ratio vs Frequency
NEGATIVE POWER SUPPLY REJECTION RATIO (dB)
120
120 G = 1000 100 G = 100 80 G = 10 60 G=1 40 20 0 10 1k 100 FREQUENCY (Hz)
POSITIVE POWER SUPPLY REJECTION RATIO (dB)
COMMON MODE REJECTION RATIO (dB)
110 100 90 80 70 60 50 40 10 100 1k FREQUENCY (Hz) G = 10
VS = 5V, 0V VREF = 2.5V
G = 100, 1000 G=1
Output Impedance vs Frequency
10k VS = 5V, 0V VREF = 2.5V
100 90 80 OVERSHOOT (%) 70 60 50 40 30 20 10
OUTPUT IMPEDANCE ()
1k
100
10
1 100
10
UW
-55C
1879 G09
Gain vs Frequency
80 70 60 50 G = 1000 VS = 5V, 0V VREF = 2.5V 0.050
Slew Rate vs Temperature
VS = 5V, 0V 0.045 VREF = 2.5V G=1 0.040 RL = 20k
OUTPUT VOLTAGE SWING--SINKING (V)
0.035 RISING 0.030 0.025 0.020 0.015 0.010 - 50 - 25 0 75 50 25 TEMPERATURE (C) 100 125 FALLING
G = 10
G=1
-20 100
1k 10k FREQUENCY (Hz)
100k
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Negative Power Supply Rejection Ratio vs Frequency
VS = 5V, 0V VREF = 2.5V
120 100
Positive Power Supply Rejection Ratio vs Frequency
VS = 5V, 0V VREF = 2.5V G = 100, 1000 80 G=1 60 G = 10 40 20 0 10 100 1k FREQUENCY (Hz) 10k 20k
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10k 20k
10k 20k
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Overshoot vs Capacitive Load
VS = 5V, 0V VREF = 2.5V VOUT = 100mVP-P
AV = 1 AV = 10 AV 100 1 10 100 CAPACITIVE LOAD (pF) 1000
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0
1k 10k FREQUENCY (Hz)
100k
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LT1789-1 TYPICAL PERFOR A CE CHARACTERISTICS
Large-Signal Transient Response Large-Signal Transient Response
5V/DIV
G = 1, 10, 100 VS = 15V RL = 20k CL = 50pF
500s/DIV
1789-1 G14
5V/DIV
Small-Signal Transient Response
20mV/DIV
G=1 VS = 5V, 0V VREF = 2.5V RL = 20k CL = 50pF
100s/DIV
1789-1 G16
20mV/DIV
Small-Signal Transient Response
20mV/DIV
G = 100 VS = 5V, 0V VREF = 2.5V RL = 20k CL = 50pF
200s/DIV
1789-1 G18
20mV/DIV
UW
G = 1000 VS = 15V RL = 20k CL = 50pF
2ms/DIV
1789-1 G15
Small-Signal Transient Response
G = 10 VS = 5V, 0V VREF = 2.5V RL = 20k CL = 50pF
100s/DIV
1789-1 G17
Small-Signal Transient Response
G = 1000 VS = 5V, 0V VREF = 2.5V RL = 20k CL = 50pF
2ms/DIV
1789-1 G19
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BLOCK DIAGRA W
V+ V+ 100k 5.7k +IN 3 RG 1 V+ V- V- VB V
+
V RG 8 5.7k
+
100k
-IN 2
V-
V- VB
Figure 1. Block Diagram
APPLICATIO S I FOR ATIO
Input and Output Offset Voltage
The offset voltage of the LT1789-1 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 110k resistors around the difference amplifier. The output
12
+ +
A3 V-
+
-
A1
110k
110k 5 REF
-
V+
-
A2
110k
110k 6 OUT
V- 7 V+ 4 V-
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voltage of the LT1789-1 (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 22 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. Care must be taken to prevent the outputs of the input buffer amplifiers (A1, A2) from saturating. This problem can occur when the gain is greater than one and the inputs approach either the negative supply (-VS) or the positive supply (+VS). As the LT1789-1 Block Diagram (Figure 1)
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LT1789-1
APPLICATIO S I FOR ATIO
-IN RG +IN
1 10mV ADJUSTMENT RANGE
LT1880 3
For inputs operating near -VS, the maximum differential input voltage can be found by adding 0.5V to the difference between -VS and the input closest to -VS, and dividing this voltage by 100k/RG. For example, with VS = 5V, 0V; -IN = 1V; RG = 22.2k (G = 10), VREF = -VS, the maximum differential input voltage will be equal to: (1V + 0.5V)/(100k/22.2k) = 0.333V Since the negative input (-IN) is equal to 1V, the output of A1 will saturate if the positive input (+IN) exceeds 1.333V. For inputs operating near +VS, 0.5V must be subtracted from the difference between +VS and the input closest to +VS, and again dividing by 100k/RG. For example, with VS = 5V,0V; +IN = 4V; RG = 50k (G = 5), VREF = -VS, the maximum differential input voltage will be equal to: (1V - 0.5V)/(100k/50k) = 0.25V In this case, since the positive input is equal to 4V, the output of A2 will saturate if the negative input goes below 3.75V. Output Offset Trimming The LT1789-1 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
Figure 2. Optional Trimming of Output Offset Voltage
offset adjust circuit. The op amp buffer provides a low impedance to the REF pin where resistance must be kept to a minimum for best CMRR and lowest gain error. Input Bias Current Return Path The low input bias current of the LT1789-1 (19nA) and the high input impedance (1.6G) allow the use of high impedance sources without introducing significant offset voltage errors, even when the full common mode range is 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 high and exceed the input common mode range of the LT1789-1, 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. The need for input resistors is eliminated if a center tap is present as shown in the third example.
-
+
+
1 8 3
-
LT1789-1 REF 5 2 10mV 100 10k 100 -10mV 6 OUTPUT V+ V-
1789 F02
shows, the gain pins of A1 and A2 sit about 0.5V above their respective inputs. This translates to approximately 0.5V of output swing before saturation occurs when one of the inputs is at its common mode limit (- V S or +VS - 1V). The combinations of gain and input voltage that can cause output saturation are too many to enumerate. However, the maximum allowable differential input voltage for a valid output can be closely approximated by the following relationships:
U
2
1789f
W
UU
13
LT1789-1
APPLICATIO S I FOR ATIO
-
THERMOCOUPLE RG LT1789-1
MICROPHONE, HYDROPHONE, ETC
RG
LT1789-1
RG
10k
200k
200k CENTER-TAP PROVIDES BIAS CURRENT RETURN
1789 F03
Figure 3. Providing an Input Common Mode Current Path
TYPICAL APPLICATIO
Single Supply Positive Integrator
VS
VIN
3 8 1 2
+
7
R1 6 10k
VS 3
LT1789-1 REF 5
+
LT1636 1 VOUT
+
-
4
C1 100F
R2 10 RESET
4
-
2
1789 TA01
VS = 2.7V TO 32V TIME CONSTANT = (R1)(C1) = 1 SECOND AS SHOWN
14
-
LT1789-1
+
- +
U
1789f
W
U
UU
+
LT1789-1
PACKAGE DESCRIPTION
S8 Package 8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0- 8 TYP
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)
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
0.189 - 0.197* (4.801 - 5.004) 8 7 6 5
0.228 - 0.244 (5.791 - 6.197)
0.150 - 0.157** (3.810 - 3.988)
1
2
3
4
0.053 - 0.069 (1.346 - 1.752)
0.004 - 0.010 (0.101 - 0.254)
0.050 (1.270) BSC
SO8 1298
1789f
15
LT1789-1
TYPICAL APPLICATIO U
Voltage Controlled Current Source
3V TO 32V VIN 3 8 RG 1 2
+
7 6 R1 1k
LT1789-1 REF 5
-
4 IL LOAD
IL = AV * VIN/R1 AV = 1 + 200k RG
1789 TA02
RELATED PARTS
PART NUMBER LTC1100 LT1101 LT1102 LT1167 LT1168 LTC 1418 LT1460 LT1468 LTC1562 LTC1605
(R)
DESCRIPTION Precision Chopper-Stabilized Instrumentation Amplifier Precision, Micropower, Single Supply Instrumentation Amplifier High Speed, JFET Instrumentation Amplifier Single Resistor Gain Programmable, Precision Instrumentation Amplifier Low Power, Single Resistor Programmable Instrumentation Amplifier 14-Bit, Low Power, 200ksps ADC with Serial and Parallel I/O Precision Series Reference 16-Bit Accurate Op Amp, Low Noise Fast Settling Active RC Filter 16-Bit, 100ksps, Sampling ADC
COMMENTS Best DC Accuracy Fixed Gain of 10 or 100, IS < 105A Fixed Gain of 10 or 100, 30V/s Slew Rate Gain Error: 0.08% Max, Gain Nonlinearity: 10ppm Max, 60V Max Input Offset Voltage, 90dB Min CMRR ISUPPLY = 530A Max Single Supply 5V or 5V Operation, 1.5LSB INL and 1LSB DNL Max Micropower; 2.5V, 5V, 10V Versions; High Precision 16-Bit Accuracy at Low and High Frequencies, 90MHz GBW, 22V/s, 900ns Settling Lowpass, Bandpass, Highpass Responses; Low Noise, Low Distortion, Four 2nd Order Filter Sections Single 5V Supply, Bipolar Input Range: 10V, Power Dissipation: 55mW Typ
1789f
16
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507
q
LT/TP 1101 2K * PRINTED IN USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2001

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