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LT1996 Precision, 100A Gain Selectable Amplifier
FEATURES

DESCRIPTIO

Pin Configurable as a Difference Amplifier, Inverting and Noninverting Amplifier Difference Amplifier Gain Range 9 to 117 CMRR >80dB Noninverting Amplifier Gain Range 0.008 to 118 Inverting Amplifier Gain Range -0.08 to -117 Gain Error: <0.05% Gain Drift: < 3ppm/C Wide Supply Range: Single 2.7V to Split 18V Micropower Operation: 100A Supply Input Offset Voltage: 50V (Max) Gain Bandwidth Product: 560kHz Rail-to-Rail Output Space Saving 10-Lead MSOP and DFN Packages
The LT(R)1996 combines a precision operational amplifier with eight precision resistors to form a one-chip solution for accurately amplifying voltages. Gains from -117 to 118 with a gain accuracy of 0.05% can be achieved without any external components. The device is particularly well suited for use as a difference amplifier, where the excellent resistor matching results in a common mode rejection ratio of greater than 80dB. The amplifier features a 50V maximum input offset voltage and a gain bandwidth product of 560kHz. The device operates from any supply voltage from 2.7V to 36V and draws only 100A supply current on a 5V supply. The output swings to within 40mV of either supply rail. The internal resistors have excellent matching characteristics; variation is 0.05% over temperature with a guaranteed matching temperature coefficent of less than 3ppm/C. The resistors are also extremely stable over voltage, exhibiting a nonlinearity of less than 10ppm. The LT1996 is fully specified at 5V and 15V supplies and from -40C to 85C. The device is available in space saving 10-lead MSOP and DFN packages. For an amplifier with selectable gains from -13 to 14, see the LT1991 data sheet.
APPLICATIO S

Handheld Instrumentation Medical Instrumentation Strain Gauge Amplifiers Differential to Single-Ended Conversion
, LTC and LT are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Patents Pending.
TYPICAL APPLICATIO
Rail-to-Rail Gain = 9 Difference Amplifier
15V 450k/81 450k/27 VM(IN) VIN VP(IN) INPUT RANGE 60V RIN = 100k 4pF 450k VOUT = VREF + 9 * VIN SWING 40mV TO EITHER RAIL
PERCENTAGE OF UNITS (%)
- +
450k/9
-
450k/9 450k/27 450k/81 4pF VREF -15V
1996 TA01
+
LT1996 450k
U
Distribution of Resistor Matching
40 35 30 25 20 15 10 5 0 -0.04 0 -0.02 0.02 RESISTOR MATCHING (%) 0.04
1996 TA01b
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LT1996A G = 81
1996f
1
LT1996
ABSOLUTE
AXI U RATI GS
Total Supply Voltage (V + to V -) ............................... 40V Input Voltage (Pins P9/M9, Note 2) ....................... 60V Input Current (Pins P27/M27/P81/M81, Note 2) .................. 10mA Output Short-Circuit Duration (Note 3) ............ Indefinite Operating Temperature Range (Note 4) ...-40C to 85C Specified Temperature Range (Note 5) ....-40C to 85C
PACKAGE/ORDER I FOR ATIO
TOP VIEW P9 P27 P81 VEE REF 1 2 3 4 5 10 M9 9 M27 8 M81 7 VCC 6 OUT
ORDER PART NUMBER LT1996CDD LT1996IDD LT1996ACDD LT1996AIDD DD PART MARKING* LBPC
TOP VIEW P9 P27 P81 VEE REF 1 2 3 4 5 10 9 8 7 6 M9 M27 M81 VCC OUT
DD PACKAGE 10-LEAD (3mm x 3mm) PLASTIC DFN
TJMAX = 125C, JA = 160C/W UNDERSIDE METAL CONNECTED TO VEE (PCB CONNECTION OPTIONAL)
*Temperature and electrical grades are identified by a label on the shipping container. Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL G PARAMETER Gain Error
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. Difference amplifier configuration, VS = 5V, 0V or 15V; VCM = VREF = half supply, unless otherwise noted.
CONDITIONS VS = 15V, VOUT = 10V; RL = 10k G = 81; LT1996AMS G = 27; LT1996AMS G = 9; LT1996AMS G = 81; LT1996ADD G = 27; LT1996ADD G = 9; LT1996ADD G = 81; LT1996 G = 27; LT1996 G = 9; LT1996

GNL G/T CMRR
Gain Nonlinearity Gain Drift vs Temperature (Note 6) Common Mode Rejection Ratio, Referred to Inputs (RTI)
VS = 15V; VOUT = 10V; RL = 10k; G = 9 VS = 15V; VOUT = 10V; RL = 10k VS = 15V; G = 9; VCM = 15.3V LT1996AMS LT1996ADD LT1996 VS = 15V; G = 27; VCM = -14.5V to 14.3V LT1996AMS LT1996ADD LT1996
2
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(Note 1)
Maximum Junction Temperature DD Package ...................................................... 125C MS Package ..................................................... 150C Storage Temperature Range DD Package .......................................-65C to 125C MS Package ......................................-65C to 150C MSOP-Lead Temperature (Soldering, 10 sec)...... 300C
ORDER PART NUMBER LT1996CMS LT1996IMS LT1996ACMS LT1996AIMS MS PART MARKING* LTBPB
MS PACKAGE 10-LEAD PLASTIC MSOP TJMAX = 150C, JA = 230C/W
MIN
TYP 0.02 0.03 0.03 0.02 0.02 0.03 0.04 0.04 0.04 1 0.3
MAX 0.05 0.06 0.07 0.05 0.07 0.08 0.12 0.12 0.12 10 3
UNITS % % % % % % % % % ppm ppm/C dB dB dB dB dB dB
1996f
80 80 70 95 90 75
100 100 100 105 105 105
LT1996
ELECTRICAL CHARACTERISTICS
SYMBOL CMRR PARAMETER Common Mode Rejection Ratio (RTI)
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. Difference amplifier configuration, VS = 5V, 0V or 15V; VCM = VREF = half supply, unless otherwise noted.
CONDITIONS VS = 15V; G = 81; VCM = -14.1V to 13.9V LT1996AMS LT1996ADD LT1996 P9/M9 Inputs VS = 15V; VREF = 0V VS = 5V, 0V; VREF = 2.5V VS = 3V, 0V; VREF = 1.25V P9/M9 Inputs, P81/M81 Connected to REF VS = 15V; VREF = 0V VS = 5V, 0V; VREF = 2.5V VS = 3V, 0V; VREF = 1.25V P27/M27 Inputs VS = 15V; VREF = 0V VS = 5V, 0V; VREF = 2.5V VS = 3V, 0V; VREF = 1.25V P81/M81 Inputs VS = 15V; VREF = 0V VS = 5V, 0V; VREF = 2.5V VS = 3V, 0V; VREF = 1.25V

MIN 105 100 85 -15.5 0.84 0.98 -60 -12.6 -1.25 -14.5 0.95 1 -14.1 0.99 1
TYP 120 120 120
MAX
UNITS dB dB dB
VCM
Input Voltage Range (Note 7)
15.3 3.94 1.86 60 15.6 6.8 14.3 3.84 1.82 13.9 3.81 1.8 15 15 50 135 80 160 100 200 150 250 1 5 7.5 500 750 1000 1500
V V V V V V V V V V V V V V V V V V V V V/C nA nA pA pA pA pA VP-P VRMS VP-P VRMS nV/Hz nV/Hz
VOS
Op Amp Offset Voltage (Note 8)
LT1996AMS, VS = 5V, 0V LT1996AMS, VS = 15V
LT1996MS
25 25

LT1996DD VOS/T IB IOS Op Amp Offset Voltage Drift (Note 6) Op Amp Input Bias Current Op Amp Input Offset Current LT1996A
0.3 2.5 50 50
LT1996
Op Amp Input Noise Voltage
0.01Hz to 1Hz 0.01Hz to 1Hz 0.1Hz to 10Hz 0.1Hz to 10Hz G = 9; f = 1kHz G = 117; f = 1kHz P9 (M9 = Ground) P27 (M27 = Ground) P81 (M81 = Ground) M9 (P9 = Ground) M27 (P27 = Ground) M81 (P81 = Ground)

0.35 0.07 0.25 0.05 46 18 350 326.9 319.2 35 11.69 3.85 500 467 456 50 16.7 5.5 650 607.1 592.8 65 21.71 7.15
en RIN
Input Noise Voltage Density (Includes Resistor Noise) Input Impedance (Note 10)
k k k k k k
1996f
3
LT1996
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. Difference amplifier configuration, VS = 5V, 0V or 15V; VCM = VREF = half supply, unless otherwise noted.
SYMBOL R PARAMETER Resistor Matching (Note 9) CONDITIONS G = 81; LT1996AMS G = 27; LT1996AMS G = 9; LT1996AMS G = 81; LT1996ADD G = 27; LT1996ADD G = 9; LT1996ADD G = 81; LT1996 G = 27; LT1996 G = 9; LT1996 R/T PSRR VOUT Resistor Temperature Coefficient (Note 6) Power Supply Rejection Ratio Minimum Supply Voltage Output Voltage Swing (to Either Rail) No Load VS = 5V, 0V VS = 5V, 0V VS = 15V 1mA Load VS = 5V, 0V VS = 5V, 0V VS = 15V ISC Output Short-Circuit Current (Sourcing) Output Short-Circuit Current (Sinking) BW -3dB Bandwidth Drive Output Positive; Short Output to Ground Drive Output Negative; Short Output to VS or Midsupply G=9 G = 27 G = 81 f = 10kHz G = 9; 0.1V Step; 10% to 90% G = 81; 0.1V Step; 10% to 90% G = 9; VS = 5V, 0V; 2V Step G = 9; VS = 5V, 0V; -2V Step G = 9; VS = 15V; 10V Step G = 9; VS = 15V; -10V Step VS = 5V, 0V; VOUT = 1V to 4V VS = 15V; VOUT = 10V VS = 5V, 0V

ELECTRICAL CHARACTERISTICS
MIN
TYP 0.02 0.03 0.03 0.02 0.02 0.03 0.04 0.04 0.04 0.3 -30
MAX 0.05 0.06 0.07 0.05 0.07 0.08 0.12 0.12 0.12 3
UNITS % % % % % % % % % ppm/C ppm/C dB V mV mV mV mV mV mV mA mA mA mA kHz kHz kHz kHz s s s s s s V/s V/s
Resistor Matching Absolute Value VS = 1.35V to 18V (Note 8)
105
135 2.4 40 2.7 55 65 110 225 275 300

150

8 4 8 4
12 21 38 17 7 560 8 40 85 85 110 110
GBWP tr, tf tS
Op Amp Gain Bandwidth Product Rise Time, Fall Time Settling Time to 0.01%
SR IS
Slew Rate Supply Current
0.06 0.08
0.12 0.12 100 130 110 150 160 210
A A A A
VS = 15V
Note 1: Absolute Maximum Ratings are those beyond which the life of the device may be impaired. Note 2: The P27/M27 and P81/M81 inputs are protected by ESD diodes to the supply rails. If one of these four inputs goes outside the rails, the input current should be limited to less than 10mA. The P9/M9 inputs can
withstand 60V if P81/M81 are grounded and VS = 15V (see Applications Information section about "High Voltage CM Difference Amplifiers"). Note 3: A heat sink may be required to keep the junction temperature below absolute maximum ratings.
1996f
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LT1996
ELECTRICAL CHARACTERISTICS
Note 4: Both the LT1996C and LT1996I are guaranteed functional over the -40C to 85C temperature range. Note 5: The LT1996C is guaranteed to meet the specified performance from 0C to 70C and is designed, characterized and expected to meet specified performance from -40C to 85C but is not tested or QA sampled at these temperatures. The LT1996I is guaranteed to meet specified performance from -40C to 85C. Note 6: This parameter is not 100% tested. Note 7: Input voltage range is guaranteed by the CMRR test at VS = 15V. For the other voltages, this parameter is guaranteed by design and through correlation with the 15V test. See the Applications Information section to determine the valid input voltage range under various operating conditions. Note 8: Offset voltage, offset voltage drift and PSRR are defined as referred to the internal op amp. You can calculate output offset as follows. In the case of balanced source resistance, VOS, OUT = VOS * Noise Gain + IOS * 450k + IB * 450k * (1 - RP/RN) where RP and RN are the total resistance at the op amp positive and negative terminal respectively. Note 9: Resistors connected to the minus inputs. Resistor matching is not tested directly, but is guaranteed by the gain error test. Note 10: Input impedance is tested by a combination of direct measurements and correlation to the CMRR and gain error tests.
TYPICAL PERFOR A CE CHARACTERISTICS
Supply Current vs Supply Voltage
200 175 SUPPLY CURRENT (A) 150 125 100 75 50 25 0 0 2 4 6 8 10 12 14 16 18 20 SUPPLY VOLTAGE (V)
1996 G01
TA = 85C TA = 25C TA = -40C
OUTPUT VOLTAGE SWING (mV)
OUTPUT VOLTAGE (mV)
Output Voltage Swing vs Load Current (Output High)
VCC -100
OUTPUT VOLTAGE SWING (mV)
OUTPUT SHORT-CIRCUIT CURRENT (mA)
VS = 5V, 0V
-200 -300 -400 -500 -600 -700 -800 -900 -1000 0 1 2 TA = 85C TA = 25C
TA = -40C
20
INPUT OFFSET VOLTAGE (V)
34567 LOAD CURRENT (mA)
UW
8 9 10
1996 G04
(Difference Amplifier Configuration) Output Voltage Swing vs Load Current (Output Low)
VCC -20
Output Voltage Swing vs Temperature
VS = 5V, 0V NO LOAD OUTPUT HIGH (RIGHT AXIS)
1400 1200 1000 800
VS = 5V, 0V TA = 85C
-40 -60
TA = 25C 600 TA = -40C 400 200 VEE
60 40 20 OUTPUT LOW (LEFT AXIS)
VEE -50 -25
0
25
50
75
100
125
0
1
2
TEMPERATURE (C)
1996 G02
34567 LOAD CURRENT (mA)
8
9
10
1996 G03
Output Short-Circuit Current vs Temperature
25
Input Offset Voltage vs Difference Gain
150 VS = 5V, 0V REPRESENTATIVE PARTS
VS = 5V, 0V SINKING
100 50 0 -50 -100 -150
15
10
SOURCING
5
0 -50 -25
50 25 0 75 TEMPERATURE (C)
100
125
1996 G05
9 18 27 36 45 54 63 72 81 90 99 108 117 GAIN (V/V) 1996 G06
1996f
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LT1996 TYPICAL PERFOR A CE CHARACTERISTICS
Output Offset Voltage vs Difference Gain
10.0
OUTPUT OFFSET VOLTAGE (mV)
7.5 5.0 2.5 0 -2.5 -5.0 -7.5
VS = 5V, 0V REPRESENTATIVE PARTS
SLEW RATE (V/s)
GAIN ERROR (%)
-10.0
9 18 27 36 45 54 63 72 81 90 99 108 117 GAIN (V/V)
1996 G07
Bandwidth vs Gain
40 35
-3dB BANDWIDTH (kHz)
VS = 5V, 0V TA = 25C
30
CMRR (dB)
PSRR (dB)
25 20 15 10 5 0 9 18 27 36 45 54 63 72 81 90 99 108 117 GAIN (V/V)
1996 G10
Output Impedance vs Frequency
1000 VS = 5V, 0V TA = 25C
100
OUTPUT IMPEDANCE ()
GAIN ERROR (%)
10 GAIN = 81 1 GAIN = 27 GAIN = 9 0.1
CMRR (dB)
0.01 1 10 100 1k FREQUENCY (Hz) 10k 100k
1996 G13
6
UW
(Difference Amplifier Configuration)
Gain Error vs Load Current
0.04 0.03 0.02 0.01 0 -0.01 -0.02 -0.03 -0.04 0 REPRESENTATIVE UNITS 1 3 LOAD CURRENT (mA) 2 4 5
1996 G08
Slew Rate vs Temperature
0.30 0.25 0.20 SR- (FALLING EDGE) 0.15 SR+ (RISING EDGE) 0.10 0.05 0 -50 -25 GAIN = 9 VS = 15V VOUT = 10V
GAIN = 81 VS = 15V VOUT = 10V TA = 25C
50 25 75 0 TEMPERATURE (C)
100
125
1996 G09
CMRR vs Frequency
130 120 110 100 90 80 70 60 50 40 30 20 10 0 GAIN = 81 GAIN = 27 GAIN = 9 VS = 5V, 0V TA = 25C
120 110 100 90 80 70 60 50 40 30 20 10 0
PSRR vs Frequency
VS = 5V, 0V TA = 25C
GAIN = 81 GAIN = 9 GAIN = 27 10 100 1k 10k FREQUENCY (Hz) 100k
1996 G12
10
100
1k 10k FREQUENCY (Hz)
100k
1M
1996 G11
CMRR vs Temperature
120 100 80 60 40 20 0 -50 -25 REPRESENTATIVE UNITS 50 25 75 0 TEMPERATURE (C) 100 125 GAIN = 9 VS = 15V
0.030 0.025 0.020 0.015 0.010 0.005
Gain Error vs Temperature
GAIN = 9 VS = 15V
0 -50 -25
REPRESENTATIVE UNITS 50 25 75 0 TEMPERATURE (C) 100 125
1996 G14
1996 G15
1996f
LT1996 TYPICAL PERFOR A CE CHARACTERISTICS
Gain vs Frequency
50 VS = 5V, 0V TA = 25C
40 GAIN = 81
30
-60
PHASE (deg)
GAIN (dB)
GAIN (dB)
30 GAIN = 27 20 GAIN = 9
20 GAIN (LEFT AXIS) 10
-80 -100 -120 -140
10
0
-160 -180
0 0.5
1
10 100 FREQUENCY (kHz)
500
1996 G16
-10 0.1
1
10 FREQUENCY (kHz)
100
-200 400
OP AMP VOLTAGE NOISE (100nV/DIV)
Small Signal Transient Response, Gain = 9
50mV/DIV
10s/DIV
PI FU CTIO S
(Difference Amplifier Configuration)
P9 (Pin 1): Noninverting Gain-of-9 input. Connects a 50k internal resistor to the op amp's noninverting input. P27 (Pin 2): Noninverting Gain-of-27 input. Connects a (50k/3) internal resistor to the op amp's noninverting input. P81 (Pin 3): Noninverting Gain-of-81 input. Connects a (50k/9) internal resistor to the op amp's noninverting input. VEE (Pin 4): Negative Power Supply. Can be either ground (in single supply applications), or a negative voltage (in split supply applications). REF (Pin 5): Reference Input. Sets the output level when difference between inputs is zero. Connects a 450k internal
UW
(Difference Amplifier Configuration)
Gain and Phase vs Frequency
40 PHASE (RIGHT AXIS) VS = 5V, 0V TA = 25C -20 GAIN = 9 -40 0
0.01Hz to 1Hz Voltage Noise
VS = 15V TA = 25C MEASURED IN G =117 REFERRED TO OP AMP INPUTS
0
10 20 30 40 50 60 70 80 90 100 TIME (s)
1996 G21
1996 G17
Small Signal Transient Response, Gain = 27
Small Signal Transient Response, Gain = 81
50mV/DIV
50mV/DIV
1996 G18
20s/DIV
1996 G19
50s/DIV
1996 G20
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resistor to the op amp's noninverting input. OUT (Pin 6): Output. VOUT = VREF + 9 * (VP1 - VM1) + 27 * (VP3 - VM3) + 81 * (VP9 - VM9). VCC (Pin 7): Positive Power Supply. Can be anything from 2.7V to 36V above the VEE voltage. M81 (Pin 8): Inverting Gain-of-81 input. Connects a (50k/9) internal resistor to the op amp's inverting input. M27 (Pin 9): Inverting Gain-of-27 input. Connects a (50k/3) internal resistor to the op amp's inverting input. M9 (Pin 10): Inverting Gain-of-9 input. Connects a 50k internal resistor to the op amp's inverting input.
1996f
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LT1996
BLOCK DIAGRA W
10 M9 9 M27 8 M81 450k/81 4pF 450k/27 450k/9 7 VCC 450k 6 OUT
-
OUT
450k/9 450k/27 450k/81
+
LT1996
4pF
450k
1
P9
2
P27
3
P81
4
VEE
5
REF
1996 BD
APPLICATIO S I FOR ATIO
Introduction
The LT1996 may be the last op amp you ever have to stock. Because it provides you with several precision matched resistors, you can easily configure it into several different classical gain circuits without adding external components. The several pages of simple circuits in this data sheet demonstrate just how easy the LT1996 is to use. It can be configured into difference amplifiers, as well as into inverting and noninverting single ended amplifiers. The fact that the resistors and op amp are provided together in such a small package will often save you board space and reduce complexity for easy probing. The Op Amp The op amp internal to the LT1996 is a precision device with 15V typical offset voltage and 3nA input bias current. The input offset current is extremely low, so matching the source resistance seen by the op amp inputs will provide for the best output accuracy. The op amp inputs are not rail-to-rail, but extend to within 1.2V of VCC and 1V
8
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of VEE. For many configurations though, the chip inputs will function rail-to-rail because of effective attenuation to the +input. The output is truly rail-to-rail, getting to within 40mV of the supply rails. The gain bandwidth product of the op amp is about 560kHz. In noise gains of 2 or more, it is stable into capacitive loads up to 500pF. In noise gains below 2, it is stable into capacitive loads up to 100pF. The Resistors The resistors internal to the LT1996 are very well matched SiChrome based elements protected with barrier metal. Although their absolute tolerance is fairly poor (30%), their matching is to within 0.05%. This allows the chip to achieve a CMRR of 80dB, and gain errors within 0.05%. The resistor values are (450k/9), (450k/27), (450k/81) and 450k, connected to each of the inputs. The resistors have power limitations of 1watt for the 450k and (450k/81) resistors, 0.3watt for the (450k/27) resistors and 0.5watt for the (450k/9) resistors; however, in practice, power dissipation will be limited well below these values by the
1996f
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LT1996
APPLICATIO S I FOR ATIO
maximum voltage allowed on the input and REF pins. The 50k resistors connected to the M9 and P9 inputs are isolated from the substrate, and can therefore be taken beyond the supply voltages. The naming of the pins "P9," "P27," "P81," etc., is based on their admittances relative to the feedback and REF admittances. Because it has 9 times the admittance, the voltage applied to the P9 input has 9 times the effect of the voltage applied to the REF input. Bandwidth The bandwidth of the LT1996 will depend on the gain you select (or more accurately the noise gain resulting from the gain you select). In the lowest configurable gain of 1, the -3dB bandwidth is limited to 450kHz, with peaking of about 2dB at 280kHz. In the highest configurable gains, bandwidth is limited to 5kHz. Input Noise The LT1996 input noise is comprised of the Johnson noise of the internal resistors (4kTR), and the input voltage noise of the op amp. Paralleling all four resistors to the +input gives a 3.8k resistance, for 8nV/Hz of voltage noise. The equivalent network on the -input gives another 8nV/Hz, and the op amp 14nV/Hz. Taking their RMS sum gives a total 18nV/Hz input referred noise floor. Output noise depends on configuration and noise gain. Input Resistance The LT1996 input resistances vary with configuration, but once configured are apparent on inspection. Note that resistors connected to the op amp's -input are looking into a virtual ground, so they simply parallel. Any feedback resistance around the op amp does not contribute to input resistance. Resistors connected to the op amp's +input are looking into a high impedance, so they add as parallel or series depending on how they are connected, and whether or not some of them are grounded. The op amp +input itself presents a very high G impedance. In the
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classical noninverting op amp configuration, the LT1996 presents the high input impedance of the op amp, as is usual for the noninverting case. Common Mode Input Voltage Range The LT1996 valid common mode input range is limited by three factors: 1. Maximum allowed voltage on the pins 2. The input voltage range of the internal op amp 3. Valid output voltage The maximum voltage allowed on the P27, M27, P81 and M81 inputs includes the positive and negative supply plus a diode drop. These pins should not be driven more than a diode drop outside of the supply rails. This is because they are connected through diodes to internal manufacturing post-package trim circuitry, and through a substrate diode to VEE. If more than 10mA is allowed to flow through these pins, there is a risk that the LT1996 will be detrimmed or damaged. The P9 and M9 inputs do not have clamp diodes or substrate diodes or trim circuitry and can be taken well outside the supply rails. The maximum allowed voltage on the P9 and M9 pins is 60V. The input voltage range of the internal op amp extends to within 1.2V of VCC and 1V of VEE. The voltage at which the op amp inputs common mode is determined by the voltage at the op amp's +input, and this is determined by the voltages on pins P9, P27, P81 and REF. (See "Calculating Input Voltage Range" section.) This is true provided that the op amp is functioning and feedback is maintaining the inputs at the same voltage, which brings us to the third requirement. For valid circuit function, the op amp output must not be clipped. The output will clip if the input signals are attempting to force it to within 40mV of its supply voltages. This usually happens due to too large a signal level, but it can also occur with zero input differential and must therefore be included as an example of a common mode problem.
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LT1996
APPLICATIO S I FOR ATIO
Consider Figure 1. This shows the LT1996 configured as a gain of 117 difference amplifier on a single supply with
RG
5V 7 8 450k/81 450k
4pF 9 10 VDM 0V+ VCM 2.5V 450k/27
450k/9
-
-
6 VOUT = 117 * VDM
1 2
450k/9 450k/27 450k/81
+
4pF
3
450k
REF 5 LT1996
4
1996 F01
Figure 1. Difference Amplifier Cannot Produce 0V on a Single Supply. Provide a Negative Supply, or Raise Pin 5, or Provide 400V of VDM
the output REF connected to ground. This is a great circuit, but it does not support VDM = 0V at any common mode because the output clips into ground while trying to produce 0VOUT. It can be fixed simply by declaring the valid input differential range not to extend below +0.4mV, or by elevating the REF pin above 40mV, or by providing a negative supply. Calculating Input Voltage Range Figure 2 shows the LT1996 in the generalized case of a difference amplifier, with the inputs shorted for the common mode calculation. The values of RF and RG are dictated by how the P inputs and REF pin are connected. By superposition we can write: VINT = VEXT * (RF/(RF + RG)) + VREF * (RG/(RF + RG)) Or, solving for VEXT: VEXT = VINT * (1 + RG/RF) - VREF * RG/RF But valid VINT voltages are limited to VCC - 1.2V and VEE + 1V, so: MAX VEXT = (VCC - 1.2) * (1 + RG/RF) - VREF * RG/RF and: MIN VEXT = (VEE + 1) * (1 + RG/RF) - VREF * RG/RF
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RF VCC
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-
VINT
VEXT RG
+
VEE RF VREF
1996 F02
Figure 2. Calculating CM Input Voltage Range
These two voltages represent the high and low extremes of the common mode input range, if the other limits have not already been exceeded (1 and 3, above). In most cases, the inverting inputs M9 through M81 can be taken further than these two extremes because doing this does not move the op amp input common mode. To calculate the limit on this additional range, see Figure 3. Note that, with
RF
RG VMORE VEXT MAX OR MIN VINT RG
VCC
- +
VEE RF VREF
1996 F03
Figure 3. Calculating Additional Voltage Range of Inverting Inputs
VMORE = 0, the op amp output is at VREF. From the max VEXT (the high cm limit), as VMORE goes positive, the op amp output will go more negative from VREF by the amount VMORE * RF/RG, so: VOUT = VREF - VMORE * RF/RG Or: VMORE = (VREF - VOUT) * RG/RF The most negative that VOUT can go is VEE + 0.04V, so: Max VMORE = (VREF - VEE - 0.04V) * RG/RF (should be positive) The situation where this function is negative, and therefore problematic, when VREF = 0 and VEE = 0, has already been dealt with in Figure 1. The strength of the equation is demonstrated in that it provides the three solutions
1996f
LT1996
APPLICATIO S I FOR ATIO
suggested in Figure 1: raise VREF, lower VEE, or provide some negative VMORE. Likewise, from the lower common mode extreme, making the negative input more negative will raise the output voltage, limited by VCC - 0.04V. MIN VMORE = (VREF - VCC + 0.04V) * RG/RF (should be negative) Again, the additional input range calculated here is only available provided the other remaining constraint is not violated, the maximum voltage allowed on the pin. The Classical Noninverting Amplifier: High Input Z Perhaps the most common op amp configuration is the noninverting amplifier. Figure 4 shows the textbook
RF
RG
-
VOUT
VIN
+
VOUT = GAIN * VIN GAIN = 1 + RF/RG
CLASSICAL NONINVERTING OP AMP CONFIGURATION. YOU PROVIDE THE RESISTORS.
8
450k/81
450k 4pF
9 10
450k/27 450k/9
-
6 VOUT
1 2
450k/9 450k/27 450k/81
+
4pF
3
450k LT1996 5
VIN CLASSICAL NONINVERTING OP AMP CONFIGURATION IMPLEMENTED WITH LT1991. RF = 45k, RG = 5.6k, GAIN = 9.1. GAIN IS ACHIEVED BY GROUNDING, FLOATING OR FEEDING BACK THE AVAILABLE RESISTORS TO ARRIVE AT DESIRED RF AND RG. WE PROVIDE YOU WITH <0.1% RESISTORS.
1996 F04
Figure 4. The LT1996 as a Classical Noninverting Op Amp
1996f
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representation of the circuit on the top. The LT1996 is shown on the bottom configured in a precision gain of 9.1. One of the benefits of the noninverting op amp configuration is that the input impedance is extremely high. The LT1996 maintains this benefit. Given the finite number of available feedback resistors in the LT1996, the number of gain configurations is also finite. The complete list of such Hi-Z input noninverting gain configurations is shown in Table 1. Many of these are also represented in Figure 5 in schematic form. Note that the P-side resistor inputs have been connected so as to match the source impedance seen by the internal op amp inputs. Note also that gain and noise gain are identical, for optimal precision.
Table 1. Configuring the M Pins for Simple Noninverting Gains. The P Inputs are driven as shown in the examples on the next page
Gain 1 1.08 1.11 1.30 1.32 1.33 1.44 3.19 3.7 3.89 4.21 9.1 10 11.8 28 37 82 91 109 118 M81 Output Output Output Output Float Output Output Grounded Float Grounded Grounded Grounded Float Grounded Float Float Grounded Grounded Grounded Grounded M81, M27, M9 Connection M27 Output Output Float Grounded Output Grounded Grounded Output Grounded Output Output Float Float Grounded Grounded Grounded Float Float Grounded Grounded M9 Output Grounded Grounded Output Grounded Float Grounded Output Output Float Grounded Output Grounded Output Float Grounded Float Grounded Float Grounded
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APPLICATIO S I FOR ATIO
VS+ 8 M81 9 M27 10 M9 7 VCC 6 VOUT VIN 8 M81 9 M27 10 M9
VIN
LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = 1 VS+ 8 M81 9 M27 10 M9 7 VCC
LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- VIN GAIN = 28 VS+ 8 M81 9 M27 10 M9 7 VCC
6
VOUT
VIN GAIN = 37 VS+ 8 M81 9 M27 10 M9 VOUT 7 VCC 6 VOUT
VIN
LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = 11.8
6
VIN
VS+ 8 M81 9 M27 10 M9 7 VCC 6 VOUT 8 M81 9 M27 10 M9
VIN
LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS-
GAIN = 109
Figure 5. Some Implementations of Classical Noninverting Gains Using the LT1996. High Input Z Is Maintained
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VS+ 7 VCC 6 VOUT 8 M81 9 M27 10 M9 VS+ 7 VCC 6 VOUT LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = 10 VS+ 8 M81 9 M27 10 M9 7 VCC 6 VOUT 8 M81 9 M27 10 M9 VIN LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = 3.893 VS+ 7 VCC 6 VOUT LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- VIN GAIN = 9.1 VS+ 8 M81 9 M27 10 M9 7 VCC 6 VOUT LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- VIN GAIN = 82 VS+ 7 VCC 6 VOUT GAIN = 91 LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- VIN GAIN = 118
1996 F05
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1996f
LT1996
APPLICATIO S I FOR ATIO
Attenuation Using the P Input Resistors Attenuation happens as a matter of fact in difference amplifier configurations, but it is also used for reducing peak signal level or improving input common mode range even in single ended systems. When signal conditioning indicates a need for attenuation, the LT1996 resistors are ready at hand. The four precision resistors can provide several attenuation levels, and these are tabulated in Table 2 as a design reference.
VIN RA VINT RG VIN OKAY UP TO 60V 1 2 450k/9 450k/27 450k/81 VINT
+
VINT = A * VIN A = RG/(RA + RG)
3
450k LT1996 5
CLASSICAL ATTENUATOR
LT1991 ATTENUATING TO THE +INPUT BY DRIVING AND GROUNDING AND FLOATING INPUTS RA = 50k, RG = 50k/9, SO A = 0.1.
1996 F06
Figure 6. LT1996 Provides for Easy Attenuation to the Op Amp's +Input. The P9 Input Can Be Taken Well Outside of the Supplies
Because the attenuations and the noninverting gains are set independently, they can be combined. This provides high gain resolution, about 700 unique gains between 0.0085 and 118, as plotted in Figure 7. This is too large a number to tabulate, but the designer can calculate achievable gain by taking the vector product of the gains and attenuations in Tables 1 and 2, and seeking the best match. Average gain resolution is 1.5%, with worst case steps of about 50% as seen in Figure 7.
1000 100 10
GAIN
1 0.1 0.01
0.001
0
100
200
300 400 COUNT
500
600
700
1996 F07
Figure 7. Over 600 Unique Gain Settings Achievable with the LT1996 by Combining Attenuation with Noninverting Gain
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Table 2. Configuring the P Pins for Various Attenuations. Those Shown in Bold Are Functional Even When the Input Drive Exceeds the Supplies
A 0.0085 0.0092 0.0110 0.0122 0.0270 0.0357 0.0763 0.0769 0.0847 0.0989 0.1 0.110 0.229 0.231 0.237 0.243 0.248 0.25 0.25 0.257 0.270 0.305 0.308 0.314 0.686 0.692 0.695 0.730 0.743 0.75 0.752 0.757 0.763 0.769 0.771 0.890 0.9 0.901 0.915 0.923 0.924 0.964 0.973 0.988 0.989 0.991 0.992 P81 Grounded Grounded Grounded Grounded Float Float Grounded Grounded Grounded Grounded Grounded Grounded Grounded Grounded Grounded Float Grounded Float Grounded Grounded Float Grounded Grounded Grounded Driven Driven Driven Float Driven Float Driven Float Driven Driven Driven Driven Float Driven Driven Driven Driven Float Float Driven Driven Driven Driven P81, P27, P9, REF Connection P27 P9 REF Grounded Grounded Driven Grounded Float Driven Float Grounded Driven Float Float Driven Grounded Grounded Driven Grounded Float Driven Grounded Driven Grounded Grounded Driven Float Grounded Driven Driven Float Driven Grounded Float Driven Float Float Driven Driven Driven Grounded Grounded Driven Grounded Float Driven Grounded Driven Grounded Driven Grounded Driven Float Grounded Grounded Driven Float Driven Float Float Driven Float Driven Grounded Driven Driven Driven Driven Grounded Driven Driven Float Driven Driven Driven Grounded Grounded Grounded Grounded Grounded Float Grounded Grounded Driven Driven Grounded Grounded Grounded Float Grounded Driven Grounded Float Grounded Float Driven Driven Grounded Driven Grounded Driven Grounded Grounded Driven Float Grounded Driven Driven Float Grounded Grounded Float Driven Grounded Float Grounded Driven Driven Grounded Grounded Driven Grounded Float Driven Grounded Driven Driven Float Grounded Driven Driven Grounded Float Float Grounded Float Driven Grounded Driven Float Grounded Driven Driven Grounded
1996f
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LT1996
APPLICATIO S I FOR ATIO
Inverting Configuration The inverting amplifier, shown in Figure 8, is another classical op amp configuration. The circuit is actually identical to the noninverting amplifier of Figure 4, except that VIN and GND have been swapped. The list of available gains is shown in Table 3, and some of the circuits are shown in Figure 9. Noise gain is 1+|Gain|, as is the usual case for inverting amplifiers. Again, for the best DC performance, match the source impedance seen by the op amp inputs.
RF
RG VIN
-
VOUT
+
VOUT = GAIN * VIN GAIN = - RF/RG
CLASSICAL INVERTING OP AMP CONFIGURATION. YOU PROVIDE THE RESISTORS.
VIN (DRIVE)
8
450k/81
450k 4pF
9 10
450k/27 450k/9
-
6 VOUT
1 2
450k/9 450k/27 450k/81
+
4pF
3
450k LT1996 5
CLASSICAL INVERTING OP AMP CONFIGURATION IMPLEMENTED WITH LT1991. RF = 45k, RG = 5.55k, GAIN = -8.1. GAIN IS ACHIEVED BY GROUNDING, FLOATING OR FEEDING BACK THE AVAILABLE RESISTORS TO ARRIVE AT DESIRED RF AND RG. WE PROVIDE YOU WITH <0.1% RESISTORS.
1996 F08
Figure 8. The LT1996 as a Classical Inverting Op Amp. Note the Circuit Is Identical to the Noninverting Amplifier, Except that VIN and Ground Have Been Swapped
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Table 3. Configuring the M Pins for Simple Inverting Gains
Gain -0.083 -0.110 -0.297 -0.321 -0.329 -0.439 -2.19 -2.7 -2.89 -3.21 -8.1 -9 -10.8 -27 -36 -81 -90 -108 -117 M81 Output Output Output Float Output Output Drive Float Drive Drive Drive Float Drive Float Float Drive Drive Drive Drive M81, M27, M9 Connection M27 Output Float Drive Output Drive Drive Output Drive Output Output Float Float Drive Drive Drive Float Float Drive Drive M9 Drive Drive Output Drive Float Drive Output Output Float Drive Output Drive Output Float Drive Float Drive Float Drive
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LT1996
APPLICATIO S I FOR ATIO
VS + 8 M81 9 M27 10 M9 7 VCC 6 VOUT 8 M81 9 M27 10 M9
VIN
VIN
LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = -0.321 VS + VIN 8 M81 9 M27 10 M9 7 VCC
LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = -27 VS + VIN 8 M81 9 M27 10 M9 7 VCC
6
VIN VOUT
VIN 6
LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = -10.8
VOUT
VS + VIN 8 M81 9 M27 10 M9 7 VCC 6 VOUT 8 M81 9 M27 10 M9
LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = -108
Figure 9. It Is Simple to Get Precision Inverting Gains with the LT1996. Input Impedance Varies from 3.8k (Gain = -117) to 50k (Gain = -9)
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VS + 7 VCC 6 VOUT VIN 8 M81 9 M27 10 M9 VS+ 7 VCC 6 VOUT LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = -9 VS + 8 M81 9 M27 10 M9 7 VCC 6 VOUT VIN 8 M81 9 M27 10 M9 LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = -2.89 VS+ 7 VCC 6 VOUT LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = -36 VS + 8 M81 9 M27 10 M9 7 VCC 6 VOUT VIN 8 M81 9 M27 10 M9 LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = -8.1 VS+ 7 VCC 6 VOUT LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = -81 VS + 7 VCC 6 VOUT LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = -90 VIN LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = -117
1996 F09
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LT1996
APPLICATIO S I FOR ATIO
Difference Amplifiers The resistors in the LT1996 allow it to easily make difference amplifiers also. Figure 10 shows the basic 4-resistor difference amplifier and the LT1996. A difference gain of 27 is shown, but notice the effect of the additional dashed connections. By connecting the 50k resistors in parallel, the gain is reduced by a factor of 10. Of course, with so many resistors, there are many possible gains. Table 4 shows the difference gains and how they are achieved. Note that, as for inverting amplifiers, the noise gain is 1 more than the signal gain.
Table 4. Connections Giving Difference Gains for the LT1996
Gain 0.083 0.110 0.297 0.321 0.329 0.439 2.189 2.700 2.893 3.214 8.1 9 10.8 27 36 81 90 108 117 VIN+ P9 P9 P27 P9 P27 P9, P27 P81 P27 P81 P9, P81 P81 P9 P27, P81 P27 P9, P27 P81 P9, P81 P27, P81 VIN- M9 M9 M27 M9 M27 M9, M27 M81 M27 M81 M9, M81 M81 M9 M27, M81 M27 M9, M27 M81 M9, M81 M27, M81 M9 P9 Output M27, M81 M81 M9, M81 M27 M81 M81 M9, M27 M9 M27 M27 M9 GND (REF) P27, P81 P81 P9, P81 P27 P81 P81 P9, P27 P9 P27 P27 P9
CLASSICAL DIFFERENCE AMPLIFIER IMPLEMENTED WITH LT1991. RF = 450k, RG = 16.7k, GAIN = 3. ADDING THE DASHED CONNECTIONS CONNECTS THE TWO 450k RESISTOR IN PARALLEL, SO RF IS REDUCED TO 45k. GAIN BECOMES 45k/16.7k = 2.7. VIN+ 2 PARALLEL TO CHANGE R F, R G VIN- 9 10 RG
P9, P27, P81 M9, M27, M81
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RF VIN- VIN+
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VOUT
RG
+
RF
VOUT = GAIN * (VIN+ - VIN-) GAIN = RF/RG
CLASSICAL DIFFERENCE AMPLIFIER USING THE LT1991
8
450k/81
450k 4pF
450k/27 450k/9
-
6 VOUT
1
450k/9 450k/27 450k/81
+
4pF
3
450k LT1996
5
1996 F10
Figure 10. Difference Amplifier Using the LT1996. Gain Is Set Simply by Connecting the Correct Resistors or Combinations of Resistors. Gain of 27 Is Shown, with Dashed Lines Modifying It to Gain of 2.7. Noise Gain Is Optimal
1996f
LT1996
APPLICATIO S I FOR ATIO
VS + 8 M81 9 M27 10 M9 1 P9 2 P27 VEE 3 P81 4 VS- GAIN = 0.321 VS + VIN- 8 M81 9 M27 10 M9 7 VCC 6 VOUT VIN+ VIN- 8 M81 9 M27 10 M9 7 VCC LT1996 OUT REF 5 6 VOUT VIN
+
VIN VIN
-
VIN
-
+
VIN+
LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = 27 VS +
VIN-
8 M81 9 M27 10 M9
7 VCC 6 VOUT
VIN-
VIN+
LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = 10.8
VIN+
VS + VIN- 8 M81 9 M27 10 M9 7 VCC 6 VOUT VIN- 8 M81 9 M27 10 M9
VIN+
LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = 108
Figure 11. Many Difference Gains Are Achievable Just by Strapping the Pins
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VS + 8 M81 9 M27 10 M9 7 VCC 6 VOUT VIN- 8 M81 9 M27 10 M9 VS+ 7 VCC 6 VOUT LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = 9 VS + 7 VCC 6 VOUT VIN- 8 M81 9 M27 10 M9 VIN+ LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = 2.89 VS+ 7 VCC 6 VOUT LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = 36 VS + 8 M81 9 M27 10 M9 7 VCC 6 VOUT VIN- 8 M81 9 M27 10 M9 VIN+ LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = 8.1 VS+ 7 VCC 6 VOUT LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = 81 VS + 7 VCC 6 VOUT VIN+ LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = 90 VIN+ LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = 117
1996 F11
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LT1996
APPLICATIO S I FOR ATIO
RF
VIN
-
RG
-
VOUT
VIN+
RG
+
RF
VOUT = GAIN * (VIN - VIN ) GAIN = RF/RG
+
CLASSICAL DIFFERENCE AMPLIFIER
Figure 12. Another Method of Selecting Difference Gain Is "Cross-Coupling." The Additional Method Means the LT1996 Provides Extra Integer Gains
Difference Amplifier: Additional Integer Gains Using Cross-Coupling Figure 12 shows the basic difference amplifier as well as the LT1996 in a difference gain of 27. But notice the effect of the additional dashed connections. This is referred to as "cross-coupling" and has the effect of reducing the differential gain from 27 to 18. Using this method, additional integer gains are achievable, as shown in Table 5 below. Note that the equations can be written by inspection from the VIN+ connections, and that the VIN- connections are simply the opposite (swap P for M and M for P). The method is the same as for the LT1991, except that the LT1996 applies a multiplier of 9. Noise gain, bandwidth, and input impedance specifications for the various cases are also tabulated, as these are not obvious. Schematics are provided in Figure 13.
Table 5. Connections Using Cross-Coupling. Note That Equations Can Be Written by Inspection of the VIN+ Column
Gain 18 54 72 VIN+ P27, M9 P81, M27 P81, M9 VIN- M27, P9 M81, P27 M81, P9 Gain Noise -3dB BW RIN RIN Equation Gain kHz Typ k Typ k 27 - 9 81 - 27 81 - 9 39 108 90 14 5 5 5 6 5 46 12 16 16 45 45 16 6 6 5 6 4
+ -
45 P81, M27, M9 M81, P27, P9 81 - 27 - 9 117 63 P81, P9, M27 M81, M9, P27 81 + 9 - 27 117 99 P81, P27, M9 M81, M27, P9 81 + 27 - 9 117
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6 VOUT
1 2
450k/9 450k/27 450k/81
+
4pF
VIN+
-
3
450k LT1996
5
CLASSICAL DIFFERENCE AMPLIFIER IMPLEMENTED WITH LT1991. RF = 450k, RG = 16.7k, GAIN = 27. GAIN CAN BE ADJUSTED BY "CROSS COUPLING." MAKING THE DASHED CONNECTIONS REDUCE THE GAIN FROM 3 T0 2. WHEN CROSS COUPLING, SEE WHAT IS CONNECTED TO THE VIN+ VOLTAGE. CONNECTING P27 AND M9 GIVES 27 - 9 = 18. CONNECTIONS TO VIN- ARE SYMMETRIC: M27 AND P9.
1996 F10
VS+ VIN- 8 M81 9 M27 10 M9 7 VCC 6 VOUT VIN- 8 M81 9 M27 10 M9
VS+ 7 VCC 6 VOUT
VIN+
LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = 18 VS+
VIN+
LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = 54 VS+
VIN-
8 M81 9 M27 10 M9
7 VCC 6
VIN-
8 M81 9 M27 10 M9
7 VCC 6
VIN+
LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = 45 VS+
VOUT
VIN+
LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = 63 VS+
VIN-
8 M81 9 M27 10 M9
7 VCC 6 VOUT
VIN-
8 M81 9 M27 10 M9
7 VCC 6 VOUT
VIN+
LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = 72
VIN+
LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 VS- GAIN = 99
1996 F13
Figure 13. Integer Gain Difference Amplifiers Using Cross-Coupling
1996f
LT1996
APPLICATIO S I FOR ATIO
High Voltage CM Difference Amplifiers
This class of difference amplifier remains to be discussed. Figure 14 shows the basic circuit on the top. The effective input voltage range of the circuit is extended by the fact that resistors RT attenuate the common mode voltage seen by the op amp inputs. For the LT1996, the most useful resistors for RG are the M9 and P9 50k resistors, because they do not have diode clamps to the supplies and therefore can be taken outside the supplies. As before, the input CM of the op amp is the limiting factor and is set by the voltage at the op amp +input, VINT. By superposition we can write: VINT = VEXT * (RF||RT)/(RG + RF||RT) + VREF * (RG||RT)/ (RF + RG||RT) + VTERM * (RF||RG)/(RT + RF||RG) Solving for VEXT: VEXT = (1 + RG/(RF||RT)) * (VINT - VREF * (RG||RT)/ (RF + RG||RT) - VTERM * (RF||RG)/(RT + RF||RG)) Given the values of the resistors in the LT1996, this equation has been simplified and evaluated, and the resulting equations provided in Table 6. As before, substituting VCC - 1.2 and VEE + 1 for VLIM will give the valid upper and lower common mode extremes respectively. Following are sample calculations for the case shown in Figure 14, right-hand side. Note that P81 and M81 are terminated so row 3 of Table 6 provides the equation: MAX VEXT = 91/9 * (VCC - 1.2V) - VREF/9 - 9 * VTERM = (10.11) * (10.8) - 0.11(2.5) - 9(10) = 18.9V and: MIN VEXT = 91/9 * (VEE + 1V) - VREF/9 - 9 * VTERM = (10.11)(1) - 0.11(2.5) - 9(10) = -80.2V but this exceeds the 60V absolute maximum rating of the P9, M9 pins, so -60V becomes the de facto negative common mode limit. Several more examples of high CM circuits are shown in Figures 15, 16, 17 for various supplies.
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Table 6. HighV CM Connections Giving Difference Gains for the LT1996
Noise Gain 10 P27, M27 P81, M81 37 91 Max, Min VEXT (Substitute VCC - 1.2, VEE + 1 for VLIM) 10/9 * VLIM - VREF/9 37/9 * VLIM - VREF/9 - 3 * VTERM 91/9 * VLIM - VREF/9 - 9 * VTERM Gain 9 9 9 9 VIN+ P9 P9 P9 P9 VIN- M9 M9 M9 M9 RT P27||P81 118 118/9 * VLIM - VREF/9 - 12 * VTERM M27||M81
RF VCC VIN- VIN+ (= VEXT) RG
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VOUT
RG
+
RT RT
VOUT = GAIN * (VIN+ - VIN-) VEE GAIN = RF/RG RF VREF
VTERM HIGH CM VOLTAGE DIFFERENCE AMPLIFIER INPUT CM TO OP AMP IS ATTENUATED BY RESISTORS RT CONNECTED TO VTERM. 12V 10V 8 450k/81 7 450k 4pF
9 10
450k/27 450k/9
-
6 VOUT
1 VIN+ VIN- INPUT CM RANGE = -60V TO 18.9V 2
450k/9 450k/27 450k/81
+
4pF
3
450k 4
REF 5 LT1996
2.5V
HIGH NEGATIVE CM VOLTAGE DIFFERENCE AMPLIFIER IMPLEMENTED WITH LT1996. RF = 450k, RG = 50k, RT 5.55k, GAIN = 9 VTERM = 10V = VCC = 12V, VREF = 2.5V, VEE = 0V.
1996 F14
Figure 14. Extending CM Input Range
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LT1996
APPLICATIO S I FOR ATIO
3V 8 M81 9 M27 10 M9 7 VCC
VIN - VIN +
6 VOUT LT1996 OUT 1 REF P9 2 5 P27 VEE 1.25V 3 P81 4
VIN - VIN +
VCM = 0.97V TO 1.86V
3V 8 M81 9 M27 10 M9 1 P9 2 P27 VEE 3 P81 4 1.25V VCM = 0.22V TO 3.5V 7 VCC LT1996 6 VOUT OUT REF 5 1.25V 8 M81 9 M27 10 M9 1 P9 2 P27 VEE 3 P81 4
VIN - VIN +
VIN - VIN +
3V 8 M81 9 M27 10 M9 7 VCC 8 M81 9 M27 10 M9
VIN - VIN +
6 LT1996 VOUT OUT 1 REF P9 2 5 P27 VEE 1.25V 3 P81 4
VIN - VIN +
1.25V VCM = -1.28V TO 6.8V VCM = 9.97V TO 18V VCM = -17V TO -8.9V
3V 8 M81 9 M27 10 M9 7 VCC 8 M81 9 M27 10 M9
VIN - VIN +
6 LT1996 VOUT OUT 1 REF P9 2 5 P27 VEE 1.25V 3 P81 4
VIN - VIN +
1.25V VCM = -2V TO 8.46V VCM = 12.9V TO 23.4V VCM = -23V TO -12.5V
1996 F15
Figure 15. Common Mode Ranges for Various LT1996 Difference Amp Configurations on VS = 3V, 0V, with Gain = 9
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3V 8 M81 9 M27 10 M9 7 VCC 6 VOUT 8 M81 9 M27 10 M9 3V 7 VCC 6 VOUT VIN - VIN + LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 3V VCM = -.78V TO 1.67V VDM <-45mV 3V 8 M81 9 M27 10 M9 3V 7 VCC VCM = 1.11V TO 2V VDM > 45mV 3V 7 VCC LT1996 6 VOUT OUT REF 5 1.25V VIN - VIN + 6 LT1996 VOUT OUT 1 REF P9 2 5 P27 VEE 1.25V 3 P81 4 VCM = 4V TO 7.26V VCM = -5V TO -1.74V 3V 7 VCC 3V 8 M81 9 M27 10 M9 3V 7 VCC 6 LT1996 VOUT OUT 1 REF P9 2 5 P27 VEE 1.25V 3 P81 4 VIN - VIN + 6 LT1996 VOUT OUT 1 REF P9 2 5 P27 VEE 1.25V 3 P81 4 3V 7 VCC 3V 8 M81 9 M27 10 M9 3V 7 VCC 6 LT1996 VOUT OUT 1 REF P9 2 5 P27 VEE 1.25V 3 P81 4 VIN - VIN + 6 LT1996 VOUT OUT 1 REF P9 2 5 P27 VEE 1.25V 3 P81 4
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APPLICATIO S I FOR ATIO
5V 8 M81 9 M27 10 M9 7 VCC 6 VOUT
VIN - VIN +
VIN - VIN +
LT1996 OUT 1 REF P9 2 5 P27 VEE 2.5V 3 P81 4
VCM = -0.83V TO 3.9V
5V 8 M81 9 M27 10 M9 1 P9 2 P27 VEE 3 P81 4 2.5V VCM = -3.7V TO 7.8V 7 VCC LT1996 OUT REF 5 2.5V 6 VOUT 8 M81 9 M27 10 M9 1 P9 2 P27 VEE 3 P81 4
VIN - VIN +
VIN - VIN +
5V 8 M81 9 M27 10 M9 7 VCC 6 VOUT 8 M81 9 M27 10 M9
VIN - VIN +
VIN - VIN +
LT1996 OUT 1 REF P9 2 5 P27 VEE 2.5V 3 P81 4 2.5V VCM = -12.6V TO 15.6V
5V 8 M81 9 M27 10 M9 7 VCC 6 VOUT 8 M81 9 M27 10 M9
VIN - VIN +
VIN - VIN +
LT1996 OUT 1 REF P9 2 5 P27 VEE 2.5V 3 P81 4 2.5V VCM = -17.1V TO 19.5V
Figure 16. Common Mode Ranges for Various LT1996 Difference Amp Configurations on VS = 5V, 0V, with Gain = 9
U
5V 8 M81 9 M27 10 M9 7 VCC 6 VOUT 8 M81 9 M27 10 M9 5V 7 VCC 6 VOUT VIN - VIN + LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 5V VCM = -0.56V TO 3.7V VDM <-5mV 5V 8 M81 9 M27 10 M9 5V 7 VCC 6 VOUT VCM = 1.1V TO 4.2V VDM > 5mV 5V 7 VCC LT1996 OUT REF 5 2.5V 6 VOUT VIN - VIN + LT1996 OUT 1 REF P9 2 5 P27 VEE 2.5V 3 P81 4 VCM = 3.8V TO 15.3V VCM = -11.7V TO 0.3V 5V 7 VCC 6 VOUT 5V 8 M81 9 M27 10 M9 5V 7 VCC 6 VOUT VIN - VIN + LT1996 OUT 1 REF P9 2 5 P27 VEE 2.5V 3 P81 4 LT1996 OUT 1 REF P9 2 5 P27 VEE 2.5V 3 P81 4 VCM = 9.8V TO 38.1V VCM = -35.1V TO -6.8V 5V 7 VCC 6 VOUT 5V 8 M81 9 M27 10 M9 5V 7 VCC 6 VOUT VIN - VIN + LT1996 OUT 1 REF P9 2 5 P27 VEE 2.5V 3 P81 4 LT1996 OUT 1 REF P9 2 5 P27 VEE 2.5V 3 P81 4 VCM = 12.8V TO 49.5V VCM = -47.2V TO -10.5V
1996 F16
W
U
U
1996f
21
LT1996
APPLICATIO S I FOR ATIO
5V 8 M81 9 M27 10 M9 1 P9 2 P27 VEE 3 P81 4 -5V VCM = -4.4V TO 4.2V 7 VCC LT1996 OUT REF 5 6 VOUT VIN - VIN + VIN - VIN +
5V 8 M81 9 M27 10 M9 1 P9 2 P27 VEE 3 P81 4 2.5V -5V VCM = -23.9V TO 8.1V 7 VCC LT1996 OUT REF 5 6 VOUT 8 M81 9 M27 10 M9 1 P9 2 P27 VEE 3 P81 4 -5V
VIN - VIN +
VIN - VIN +
5V 8 M81 9 M27 10 M9 1 P9 2 P27 VEE 3 P81 4 7 VCC LT1996 OUT REF 5 6 VOUT 8 M81 9 M27 10 M9 1 P9 2 P27 VEE 3 P81 4 -5V -5V
VIN - VIN +
VIN - VIN +
-5V VCM = -40.4V TO 38.4V
5V 8 M81 9 M27 10 M9 1 P9 2 P27 VEE 3 P81 4 7 VCC LT1996 OUT REF 5 6 VOUT 8 M81 9 M27 10 M9 1 P9 2 P27 VEE 3 P81 4 -5V -5V
VIN - VIN +
VIN - VIN +
-5V VCM = -52.4V TO 49.8V
Figure 17. Common Mode Ranges for Various LT1996 Difference Amp Configurations on VS = 5V, with Gain = 9
22
U
5V 8 M81 9 M27 10 M9 1 P9 2 P27 VEE 3 P81 4 7 VCC LT1996 OUT REF 5 5V 6 VOUT 8 M81 9 M27 10 M9 5V 7 VCC 6 VOUT VIN - VIN + LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 -5V -5V VCM = -3.9V TO 4.8V VDM <-5mV 5V 8 M81 9 M27 10 M9 5V 7 VCC 6 VOUT -5V VCM = -5V TO 3.7V VDM > 5mV 5V 7 VCC LT1996 OUT REF 5 6 VOUT VIN - VIN + LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 -5V VCM = -31.4V TO 0.6V VCM = -16.4V TO 15.6V 5V 7 VCC LT1996 OUT REF 5 6 VOUT 5V 8 M81 9 M27 10 M9 5V 7 VCC 6 VOUT VIN - VIN + LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 -5V VCM = -60V TO -10.2V VCM = 4.6V TO 60V 5V 7 VCC LT1996 OUT REF 5 6 VOUT 5V 8 M81 9 M27 10 M9 5V 7 VCC 6 VOUT VIN - VIN + LT1996 OUT 1 REF P9 2 5 P27 VEE 3 P81 4 -5V VCM = -60V TO -10.2V
1996 F17
W
U
U
VCM = 7.6V TO 60V
1996f
LT1996
PACKAGE DESCRIPTIO U
DD Package 10-Lead Plastic DFN (3mm x 3mm)
(Reference LTC DWG # 05-08-1699)
R = 0.115 TYP 6 0.675 0.05 0.38 0.10 10 3.00 0.10 (4 SIDES) PACKAGE OUTLINE 0.25 0.05 0.50 BSC 2.38 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS PIN 1 TOP MARK (SEE NOTE 6) 5 0.200 REF 0.75 0.05 2.38 0.10 (2 SIDES) BOTTOM VIEW--EXPOSED PAD NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2). CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 1 0.25 0.05 0.50 BSC 1.65 0.10 (2 SIDES)
(DD10) DFN 1103
3.50 0.05 1.65 0.05 2.15 0.05 (2 SIDES)
0.00 - 0.05
0.889 0.127 (.035 .005)
3.00 0.102 (.118 .004) (NOTE 3) 10 9 8 7 6
0.497 0.076 (.0196 .003) REF
5.23 (.206) MIN
3.20 - 3.45 (.126 - .136)
0.254 (.010) GAUGE PLANE
DETAIL "A" 0 - 6 TYP
4.90 0.152 (.193 .006)
3.00 0.102 (.118 .004) (NOTE 4)
0.50 0.305 0.038 (.0197) (.0120 .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT
DETAIL "A" 0.18 (.007) NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
0.53 0.152 (.021 .006)
12345 1.10 (.043) MAX 0.86 (.034) REF
SEATING PLANE
0.17 - 0.27 (.007 - .011) TYP
0.50 (.0197) BSC
0.127 0.076 (.005 .003)
MSOP (MS) 0603
1996f
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.
23
LT1996
TYPICAL APPLICATIO
VP
Bidirectional Controlled Current Source
VS + 8 M81 9 M27 10 M9 1 P9 2 P27 3 P81 7 6 5 4 VS - ILOAD = 9(VIN + - VIN -) 10k R1 10k VIN
VIN - VIN +
LT1996
RELATED PARTS
PART NUMBER LT1990 LT1991 LT1995 LT6010/LT6011/LT6012 LT6013/LT6014 LTC6910-X DESCRIPTION High Voltage Difference Amplifier Precision, 100A Gain Selectable Amplifier 30MHz, 1000V/s Gain Selectable Amplifier Single/Dual/Quad Precision Op Amp Single/Dual Precision Op Amp Programmable Gain Amplifiers COMMENTS 250V Input Common Mode, Micropower, Pin Selectable Gain = 1, 10 Gain Resistors of 450k, 150k, 50k High Speed, Pin Selectable Gain = -7 to 8 Similar Performance as LT1996 Diff Amp, 135A, 14nVHz, Rail-to-Rail Out Lower Noise AV 5 Version of LT1991, 145A, 8nV/Hz, Rail-to-Rail Out 3 Gain Configurations, Rail-to-Rail Input and Output
24
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507
+
VM
U
Micropower AV = 90 Instrumentation Amplifier
10 9 8 450k/81 4pF 450k/27 450k/9 1/2 LT6011 7 450k 6 VOUT
+
-
1/2 LT6011
- +
4pF 4 5
1996 TA02
450k/9 450k/27 450k/81
LT1996 450k
-
1 2 3
AC Coupled Amplifier
VS + 8 M81 9 M27 10 M9 1 P9 2 P27 3 P81 7 6 5 4 VS - GAIN = 117 BW = 4Hz TO 5kHz VIN - VOUT VIN +
Differential Input/Output G = 9 Amplifier
VS + 8 M81 9 M27 10 M9 1 P9 2 P27 3 P81 7 6 5 10k 4 VS - USE VOCM TO SET THE DESIRED OUTPUT COMMON MODE LEVEL 10k VOUT-
1996 TA03
LT1996
LT1996
0.1F
VOUT+ VOCM
-
LT6010
LT/TP 0205 1K * PRINTED IN USA
+
1996f
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2005

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