LT1991 LINEAR | Alldatasheet
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, LTC and LT are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Patent Pending. Precision, 100µA Gain Selectable Amplifier TYPICAL APPLICATIO U FEATURES DESCRIPTIO U APPLICATIO SU ■ Pin Configurable as a Difference Amplifier, Inverting and Noninverting Amplifier ■ Difference Amplifier Gain Range 1 to 13 CMRR >75dB ■ Noninverting Amplifier Gain Range 0.07 to 14 ■ Inverting Amplifier Gain Range –0.08 to –13 ■ Gain Error <0.04% ■ Gain Drift < 3ppm/°C ■ Wide Supply Range: Single 2.7V to Split ±18V ■ Micropower: 100µA Supply Current ■ Precision: 50µV Maximum Input Offset Voltage ■ 560kHz Gain Bandwidth Product ■ Rail-to-Rail Output ■ Space Saving 10-Lead MSOP and DFN Packages ■ Handheld Instrumentation ■ Medical Instrumentation ■ Strain Gauge Amplifiers ■ Differential to Single-Ended Conversion The LT 1991 combines a precision operational amplifier with eight precision resistors to form a one-chip solution for accurately amplifying voltages. Gains from –13 to 14 with a gain accuracy of 0.04% can be achieved using no 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 75dB. The amplifier features a 50 µV 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 100µA supply current on a 5V supply. The output swings to within 40mV of either supply rail. The resistors have excellent matching, 0.04% over tem- perature for the 450k resistors. The matching temperature coefficent is guaranteed less than 3ppm/°C. The resistors are extremely linear with voltage, resulting in a gain nonlinearity of less than 10ppm. The LT1991 is fully specified at 5V and ±15V supplies and from –40 °C to 85 °C. The device is available in space saving 10-lead MSOP and low profile (0.8mm) 3mm × 3mm DFN packages. Rail-to-Rail Gain = 1 Difference Amplifier Distribution of Resistor Matching ∆VIN VM(IN) VP(IN) VOUT = VREF + ∆VIN SWING 40mV TO EITHER RAIL R OUT <0.1Ω VREF = 2.5V INPUT RANGE –0.5V TO 5.1V R IN = 900kΩ LT1991
1991 TA01
RESISTOR MATCHING (%) PERCENTAGE OF UNITS (%) 0.04 1991TA01b –0.02 0 0.02 –0.04 450k RESISTORS LT1991A
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS ∆G Gain Error V S = ±15V, VOUT = ±10V; RL = 10k G = 1; LT1991A ● ±0.04 % G = 3 or 9; LT1991A ● ±0.06 % G = 3 or 9; LT1991 ● ±0.12 % GNL Gain Nonlinearity V S = ±15V; VOUT = ±10V; RL = 10k ● 1 10 ppm ∆G/∆T Gain Drift vs Temperature (Note 6) V S = ±15V; VOUT = ±10V; RL = 10k ● 0.3 3 ppm/ °C CMRR Common Mode Rejection Ratio, V S = ±15V; VCM = ±15.2V Referred to Inputs (RTI) G = 9; LT1991A ● 80 100 dB G = 3; LT1991A ● 75 93 dB G = 1; LT1991A ● 75 90 dB Any Gain; LT1991 ● 60 70 dB VCM Input Voltage Range (Note 7) P1/M1 Inputs VS = ±15V; VREF = 0V ● –28 27.6 V VS = 5V, 0V; VREF = 2.5V ● –0.5 5.1 V VS = 3V, 0V; VREF = 1.25V ● 0.75 2.35 V ABSOLUTE AXI U RATI GSW WW U (Note 1) ELECTRICAL CHARACTERISTICSThe ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. Difference amplifier configuration, VS = 5V, 0V or ±15V; VCM = VREF = half supply, unless otherwise noted. Input Voltage Operating Temperature Range (Note 4) ...–40°C to 85°C Specified Temperature Range (Note 5) ....–40°C to 85°C ORDER PART NUMBER DD PART MARKING* TJMAX = 150°C, θJA = 230°C/W LBMM LT1991CDD LT1991IDD LT1991ACDD LT1991AIDD *Temperature and electrical grades are identified by a label on the shipping container. Consult LTC Marketing for parts specified with wider operating temperature ranges. Maximum Junction Temperature Storage Temperature Range ORDER PART NUMBER MS PART MARKING* LTQD LT1991CMS LT1991IMS LT1991ACMS LT1991AIMS EXPOSED PAD CONNECTED TO VEE PCB CONNECTION OPTIONAL TJMAX = 125°C, θJA = 160°C/W PACKAGE/ORDER I FOR ATIOUU W TOP VIEW DD PACKAGE 10-LEAD (3mm × 3mm) PLASTIC DFN 1 M1 V CC OUT V EE REF V EE REF V CC OUT TOP VIEW MS PACKAGE 10-LEAD PLASTIC MSOP
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS VCM Input Voltage Range (Note 7) P1/M1 Inputs, P9/M9 Connected to REF VS = ±15V; VREF = 0V ● –60 60 V VS = 5V, 0V; VREF = 2.5V ● –14 16.8 V VS = 3V, 0V; VREF = 1.25V ● –1.5 7.3 V P3/M3 Inputs V S = ±15V; VREF = 0V ● –15.2 15.2 V VS = 5V, 0V; VREF = 2.5V ● 0.5 4.2 V VS = 3V, 0V; VREF = 1.25V ● 0.95 1.95 V P9/M9 Inputs V S = ±15V; VREF = 0V ● –15.2 15.2 V VS = 5V, 0V; VREF = 2.5V ● 0.85 3.9 V VS = 3V, 0V; VREF = 1.25V ● 1.0 1.9 V VOS Op Amp Offset Voltage (Note 8) LT1991AMS, V S = 5V, 0V 15 50 µV
- 135 µV LT1991AMS, VS = ±15V 15 80 µV
- 160 µV LT1991MS 25 100 µV
- 200 µV LT1991DD 25 150 µV
- 250 µV ∆VOS/∆T Op Amp Offset Voltage Drift (Note 6) ● 0.3 1 µV/°C IB Op Amp Input Bias Current 2.5 5 nA
- 7.5 nA IOS Op Amp Input Offset Current LT1991A 50 500 pA
- 750 pA LT1991 50 1000 pA
- 1500 pA Op Amp Input Noise Voltage 0.01Hz to 1Hz 0.35 µVP-P 0.01Hz to 1Hz 0.07 µVRMS 0.1Hz to 10Hz 0.25 µVP-P 0.1Hz to 10Hz 0.05 µVRMS en Input Noise Voltage Density G = 1; f = 1kHz 180 nV/ √Hz G = 9; f = 1kHz 46 nV/ √Hz RIN Input Impedance (Note 10) P1 (M1 = Ground) ● 630 900 1170 k Ω P3 (M3 = Ground) ● 420 600 780 k Ω P9 (M9 = Ground) ● 350 500 650 k Ω M1 (P1 = Ground) ● 315 450 585 k Ω M3 (P3 = Ground) ● 105 150 195 k Ω M9 (P9 = Ground) ● 35 50 65 k Ω ∆R Resistor Matching 450k Resistors, LT1991A ● 0.01 0.04 % (Note 9) Other Resistors, LT1991A ● 0.02 0.06 % 450k Resistors, LT1991 ● 0.02 0.08 % Other Resistors, LT1991 ● 0.04 0.12 % ∆R/∆T Resistor Temperature Coefficient (Note 6) Resistor Matching ● 0.3 3 ppm/ °C Absolute Value ● –30 ppm/ °C PSRR Power Supply Rejection Ratio V S = ±1.35V to ±18V (Note 8) ● 105 135 dB Minimum Supply Voltage ● 2.4 2.7 V The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. Difference amplifier configuration, VS = 5V, 0V or ±15V; VCM = VREF = half supply, unless otherwise noted.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. Difference amplifier configuration, VS = 5V, 0V or ±15V; VCM = VREF = half supply, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS VOUT Output Voltage Swing (to Either Rail) No Load VS = 5V, 0V 40 55 mV VS = 5V, 0V ● 65 mV VS = ±15V ● 110 mV 1mA Load VS = 5V, 0V 150 225 mV VS = 5V, 0V ● 275 mV VS = ±15V ● 300 mV ISC Output Short-Circuit Current (Sourcing) Drive Output Positive; 8 12 mA Short Output to Ground ● 4m A Output Short-Circuit Current (Sinking) Drive Output Negative; 8 21 mA Short Output to VS or Midsupply ● 4m A BW –3dB Bandwidth G = 1 110 kHz G = 3 78 kHz G = 9 40 kHz GBWP Op Amp Gain Bandwidth Product f = 10kHz 560 kHz tr, tf Rise Time, Fall Time G = 1; 0.1V Step; 10% to 90% 3 µs G = 9; 0.1V Step; 10% to 90% 8 µs ts Settling Time to 0.01% G = 1; V S = 5V, 0V; 2V Step 42 µs G = 1; VS = 5V, 0V; –2V Step 48 µs G = 1; VS = ±15V, 10V Step 114 µs G = 1; VS = ±15V, –10V Step 74 µs SR Slew Rate V S = 5V, 0V; VOUT = 1V to 4V ● 0.06 0.12 V/ µs VS = ±15V; VOUT = ±10V ● 0.08 0.12 V/ µs IS Supply Current V S = 5V, 0V 100 110 µA
- 150 µA VS = ±15V 130 160 µA
- 210 µA Note 1: Absolute Maximum Ratings are those beyond which the life of the device may be impaired. Note 2: The P3/M3 and P9/M9 inputs should not be taken more than 0.2V beyond the supply rails. The P1/M1 inputs can withstand ±60V if P9/M9 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. Note 4: Both the LT1991C and LT1991I are guaranteed functional over the –40°C to 85°C temperature range. Note 5: The LT1991C is guaranteed to meet the specified performance from 0°C to 70°C and is designed, characterized and expected to meet specified performance from –40°C to 85°C but is not tested or QA sampled at these temperatures. The LT1991I is guaranteed to meet specified performance from –40°C to 85°C. 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, V OS,OUT = VOS • NOISEGAIN + 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: Applies to resistors that are connected to the inverting inputs. Resistor matching is not tested directly, but is guaranteed by the gain error test. Note 10: Input impedence is tested by a combination of direct measurements and correlation to the CMRR and gain error tests.
Output Voltage Swing vs Load Current (Output High) Output Short-Circuit Current vs Temperature Input Offset Voltage vs Difference Gain Output Offset Voltage vs Difference Gain Gain Error vs Load Current Slew Rate vs Temperature (Difference Amplifier Configuration) Supply Current vs Supply Voltage Output Voltage Swing vs Temperature Output Voltage Swing vs Load Current (Output Low) TYPICAL PERFOR A CE CHARACTERISTICS UW SUPPLY VOLTAGE (±V) SUPPLY CURRENT (µA) 200 175 150 125 100
1991 G01
TA = 85°C TA = –40°C TA = 25°C TEMPERATURE (°C) –50 OUTPUT VOLTAGE SWING (mV) 100
1991 G02
V EE –25 25 75 125 VS = 5V, 0V NO LOAD OUTPUT HIGH (RIGHT AXIS) OUTPUT LOW (LEFT AXIS) V CC –20 –40 –60 LOAD CURRENT (mA) OUTPUT VOLTAGE (mV) 1400 1200 1000 800 600 400 200 V EE
1991 G03
VS = 5V, 0V TA = 85°C TA = –40°C TA = 25°C LOAD CURRENT (mA) VCC –100 –200 –300 –400 –500 –600 –700 –800 –900 –1000 OUTPUT VOLTAGE SWING (mV)
1991 G04
VS = 5V, 0V TA = 85°C TA = –40°C TA = 25°C TEMPERATURE (°C) –50 OUTPUT SHORT-CIRCUIT CURRENT (mA) 0 50 75
1991 G05
–25 25 100 125 VS = 5V, 0V SINKING SOURCING GAIN (V/V) INPUT OFFSET VOLTAGE (µV) 150 100 –50 –100 –150 1291 01 1 1 35
1991 G06
VS = 5V, 0V REPRESENTATIVE PARTS GAIN (V/V) OUTPUT OFFSET VOLTAGE (µV) 1000 750 500 250 –250 –500 –750 –1000 1291 01 1 1 35
1991 G07
VS = 5V, 0V REPRESENTATIVE PARTS LOAD CURRENT (mA) GAIN ERROR (%) 3 5
1991 G08
0.04 0.03 0.02 0.01 –0.01 –0.02 –0.03 –0.04 GAIN = 1 VS = ±15V VOUT = ±10V TA = 25°C REPRESENTATIVE UNITS TEMPERATURE (°C) –50 SLEW RATE (V/µs) 0.30 0.25 0.20 0.15 0.10 0.05 25 75
1991 G09
–25 0 50 100 125 GAIN = 1 VS = ±15V VOUT = ±10V SR– (FALLING EDGE) SR+ (RISING EDGE)
TYPICAL PERFOR A CE CHARACTERISTICS UW Output Impedance vs Frequency CMRR vs Temperature Gain Error vs Temperature Gain and Phase vs FrequencyGain vs Frequency 0.01Hz to 1Hz Voltage Noise (Difference Amplifier Configuration) Bandwidth vs Gain CMRR vs Frequency PSRR vs Frequency GAIN SETTING (V/V) –3dB BANDWIDTH (kHz) 120 100 35 79
1991 G10
VS = 5V, 0V TA = 25°C FREQUENCY (Hz) CMRR (dB) 120 110 100 10 1k 10k 1M
1991 G11
VS = 5V, 0V TA = 25°CGAIN = 9 GAIN = 1 GAIN = 3 PSRR (dB) 120 110 100 VS = 5V, 0V TA = 25°C GAIN = 9 GAIN = 1 GAIN = 3 FREQUENCY (Hz) 10 1k 10k
1991 G12
FREQUENCY (Hz) OUTPUT IMPEDANCE (Ω) 1 100 1k 100k 10k
1991 G13
0.1 0.01 VS = 5V, 0V TA = 25°C GAIN = 9 GAIN = 1 GAIN = 3 TEMPERATURE (°C) –50 CMRR (dB) 120 100 25 75
1991 G14
–25 0 50 100 125 GAIN = 1 VS = ±15V REPRESENTATIVE UNITS TEMPERATURE (°C) –50 GAIN ERROR (%) 0.030 0.025 0.020 0.015 0.010 0.005 25 75
1991 G15
–25 0 50 100 125 GAIN = 1 VS = ±15V REPRESENTATIVE UNITS FREQUENCY (kHz) GAIN (dB) –10 –20 10 100 600
1991 G16
GAIN = 9 GAIN = 3 GAIN = 1 VS = 5V, 0V TA = 25°C FREQUENCY (kHz) GAIN (dB) PHASE (deg) –45 –90 –135 –180 10 100 400
1991 G17
0.5 VS = 5V, 0V TA = 25°C GAIN = 1 PHASE GAIN VS = ±15V TA = 25°C MEASURED IN G =13 REFERRED TO OP AMP INPUTS 0 1 02 03 04 05 06 07 08 09 0 1 0 0 TIME (s) OP AMP VOLTAGE NOISE (100nV/DIV)
1991 G21
P1 (Pin 1): Noninverting Gain-of-1 input. Connects a 450k internal resistor to the op amp’s noninverting input. P3 (Pin 2): Noninverting Gain-of-3 input. Connects a 150k internal resistor to the op amp’s noninverting input. P9 (Pin 3): Noninverting Gain-of-9 input. Connects a 50k 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 inter- nal resistor to the op amp’s noninverting input. OUT (Pin 6): Output. V OUT = VREF + 1 • (VP1 – VM1) + 3 • (VP3 – VM3) + 9 • (VP9 – VM9). VCC (Pin 7): Positive Power Supply. Can be anything from 2.7V to 36V above the VEE voltage. M9 (Pin 8): Inverting Gain-of-9 input. Connects a 50k internal resistor to the op amp’s inverting input. M3 (Pin 9): Inverting Gain-of-3 input. Connects a 150k internal resistor to the op amp’s inverting input. M1 (Pin 10): Inverting Gain-of-1 input. Connects a 450k internal resistor to the op amp’s inverting input. Exposed Pad: Must be soldered to PCB. (Difference Amplifier Configuration) Small Signal Transient Response Small Signal Transient Response Small Signal Transient Response TYPICAL PERFOR A CE CHARACTERISTICS UW 50mV/DIV 5µs/DIV GAIN = 1
1991 G18
5µs/DIV
1991 G19
GAIN = 3 50mV/DIV 5µs/DIV GAIN = 9
1991 G20
The LT1991 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 compo- nents. The several pages of simple circuits in this data sheet demonstrate just how easy the LT1991 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 LT1991 is a precision device with 15µV typical offset voltage and 3nA input bias cur- rent. The input offset current is extremely low, so match- ing 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 V CC and 1V 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 LT1991 are very well matched SiChrome based elements protected with barrier metal. Although their absolute tolerance is fairly poor ( ±30%), their matching is to within 0.04%. This allows the chip to achieve a CMRR of 75dB, and gain errors within 0.04%. The resistor values are 50k, 150k, and 2 of 450k, con- nected to each of the inputs. The resistors have power limitations of 1watt for the 450k resistors, 0.3watt for the 150k resistors and 0.5watt for the 50k resistors; however, in practice, power dissipation will be limited well below these values by the maximum voltage allowed on the input and REF pins. The 450k resistors connected to the M1 and P1 inputs are isolated from the substrate, and can there- fore be taken beyond the supply voltages. The naming of the pins “P1,” “P3,” “P9,” etc., is based on their relative 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 P1 input. Bandwidth The bandwidth of the LT1991 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 32kHz. Input Noise The LT1991 input noise is dominated by the Johnson noise of the internal resistors (√4kTR). Paralleling all four resistors to the +input gives a 32.1k Ω resistance, for 23nV/√Hz of voltage noise. The equivalent network on the –input gives another 23nV/√Hz, and taking their RMS sum gives a total 33nV/√Hz input referred noise floor. Output noise depends on configuration and noise gain. Input Resistance The LT1991 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 Ω impedance. In the classical noninverting op amp configuration, the LT1991 presents the high input impedance of the op amp, as is usual for the noninverting case. Common Mode Input Voltage Range The LT1991 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 APPLICATIO S I FOR ATIOWU UU
be included as an example of a common mode problem. dictated by how the P inputs and REF pin are connected. Figure 1. Difference Amplifier Cannot Produce Figure 2. Calculating CM Input Voltage Range
1991 F01
1991 F02
shown on the bottom configured in a precision gain of 5.5. Table 1. Many of these are also represented in Figure 5 in noise gain are identical, for optimal precision. Figure 3. Calculating Additional voltage, limited by VCC – 0.04V. Figure 4. The LT1991 as a Classical Noninverting Op Amp
1991 F03
1991 F04
CLASSICAL NONINVERTING OP AMP CONFIGURATION. IMPLEMENTED WITH LT1991. RF = 225k, RG = 50k, GAIN = 5.5. THE AVAILABLE RESISTORS TO ARRIVE AT DESIRED RF AND RG. WE PROVIDE YOU WITH <0.1% RESISTORS. violated, the maximum voltage allowed on the pin.
Table 1. Configuring the M Pins for Simple Noninverting Gains.
1 Output Output Output
1.077 Output Output Ground
1.1 Output Float Ground
1.25 Float Output Ground
1.273 Output Ground Output
1.3 Output Ground Float
1.4 Output Ground Ground
2 Float Float Ground
2.5 Float Ground Output
2.8 Ground Output Output
3.25 Ground Output Float
3.5 Ground Output Ground
4 Float Ground Float
5 Float Ground Ground
5.5 Ground Float Output
7 Ground Ground Output
10 Ground Float Float
11 Ground Float Ground
13 Ground Ground Float
14 Ground Ground Ground
Figure 5. Some Implementations of Classical Noninverting
1991 F05
Figure 6. LT1991 Provides for Easy Attenuation to the Op Amp’s Figure 7. Over 346 Unique Gain Settings Achievable with the Table 2 as a design reference. attenuations in Tables 1 and 2, and seeking the best match. Average gain resolution is 1.5%, with a worst case of 7%. Table 2. Configuring the P Pins for Various Attenuations. Those
0.0714 Ground Ground Drive Ground
0.0769 Ground Ground Drive Float
0.0909 Ground Float Drive Ground
0.1 Ground Float Drive Float
0.143 Ground Ground Drive Drive
0.182 Ground Float Drive Drive
0.2 Float Ground Drive Ground
0.214 Ground Drive Ground Ground
0.231 Ground Drive Float Ground
0.25 Float Ground Drive Float
0.286 Ground Drive Drive Ground
0.308 Ground Drive Drive Float
0.357 Ground Drive Drive Drive
0.4 Float Ground Drive Drive
0.5 Float Float Drive Ground
0.6 Float Drive Ground Ground
0.643 Drive Ground Ground Ground
0.692 Drive Ground Float Ground
0.714 Drive Ground Drive Ground
0.75 Float Drive Float Ground
0.769 Drive Ground Drive Float
0.786 Drive Ground Drive Drive
0.8 Float Drive Drive Ground
0.818 Drive Float Ground Ground
0.857 Drive Drive Ground Ground
0.9 Drive Float Float Ground
0.909 Drive Float Drive Ground
0.923 Drive Drive Float Ground
0.929 Drive Drive Drive Ground
1 Drive Drive Drive Drive
1991 F06
1991 F07
Table 3. Configuring the M Pins for Simple Inverting Gains Figure 8. The LT1991 as a Classical Inverting Op Amp.
1991 F08
CLASSICAL INVERTING OP AMP CONFIGURATION. THE AVAILABLE RESISTORS TO ARRIVE AT DESIRED RF AND RG. WE PROVIDE YOU WITH <0.1% RESISTORS.
Figure 9. It Is Simple to Get Precision Inverting Gains with the LT1991.
1991 F09
Figure 10. Difference Amplifier Using the LT1991. Gain Is Set shows the difference gains and how they are achieved. Table 4. Connections Giving Difference Gains for the LT1991
0.077 P1 M1 M3, M9 P3, P9
0.1 P1 M1 M9 P9
0.25 P1 M1 M3 P3
0.273 P3 M3 M1, M9 P1, P9
0.3 P3 M3 M9 P9
0.4 P1, P3 M1, M3 M9 P9
1 P1 M1
1.5 P3 M3 M1 P1
1.8 P9 M9 M1, M3 P1, P3
2.25 P9 M9 M3 P3
2.5 P1, P9 M1, M9 M3 P3
4 P1, P3 M1, M3
4.5 P9 M9 M1 P1
6 P3, P9 M3, M9 M1 P1
10 P1, P9 M1, M9
12 P3, P9 M3, M9
13 P1, P3, P9 M1, M3, M9
1991 F10
Figure 11. Many Difference Gains Are Achievable Just by Strapping the Pins
1991 F11
Figure 12. Another Method of Selecting Difference Gain Is “Cross-Coupling.” Figure 13. Integer Gain Difference tions are simply the opposite (swap P for M and M for P). not obvious. Schematics are provided in Figure 13. Table 5. Connections Using Cross-Coupling. Note That Equations
2 P3, M1 M3, P1 3 – 1 5 70 281 141
5 P9, M3, M1 M9, P3, P1 9 – 3 – 1 14 32 97 49
7 P9, P1, M3 M9, M1, P3 9 + 1 – 3 14 32 121 44
8 P9, M1 M9, P1 9 – 1 11 38 248 50
11 P9, P3, M1 M9, M3, P1 9 + 3 – 1 14 32 242 37
*Gain of 6 is better implemented as shown previously, but is included here for completeness. DASHED CONNECTIONS REDUCE THE GAIN FROM 3 T0 2. + VOLTAGE. CONNECTING P3 AND M1 GIVES +3 –1 = 2.
1991 F13
This class of difference amplifier remains to be discussed. upper and lower common mode extremes respectively. Figure 14. Extending CM Input Range Table 6. HighV CM Connections Giving Difference Gains
1 P1 M1 2 2 • V LIM - VREF
1 P1 M1 P3, M3 5 5 • V LIM – VREF – 3 • VTERM
1 P1 M1 P9, M9 11 11 • V LIM – VREF – 9 • VTERM
1 P1 M1 P3||P9 14 14 • V LIM – VREF – 12 • VTERM
1991 F14
RESISTORS RT CONNECTED TO VTERM. VTERM = VCC = 12V, VREF = 2.5V, VEE = GROUND.
1991 F15
Figure 15. Common Mode Ranges for Various LT1991 Configurations on VS = 3V, 0V; with Gain = 1
1991 F16
Figure 16. Common Mode Ranges for Various LT1991 Configurations on VS = 5V, 0V; with Gain = 1
Figure 17. Common Mode Ranges for Various LT1991 Configurations on VS = ±5V, with Gain = 1
1991 F17
(Reference LTC DWG # 05-08-1661) UPACKAGE DESCRIPTIO 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 represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. MSOP (MS) 0603 0.53 ± 0.152 (.021 ± .006) SEATING PLANE 0.18 (.007) 1.10 (.043) MAX 0.17 – 0.27 (.007 – .011) TYP 0.127 ± 0.076 (.005 ± .003) 0.86 (.034) REF 0.50 (.0197) BSC 12 3 45 4.90 ± 0.152 (.193 ± .006) 0.497 ± 0.076 (.0196 ± .003) REF8910 7 6 3.00 ± 0.102 (.118 ± .004) (NOTE 3) 3.00 ± 0.102 (.118 ± .004) (NOTE 4) 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 0.254 (.010) 0° – 6° TYP DETAIL “A” DETAIL “A” GAUGE PLANE 5.23 (.206) MIN 3.20 – 3.45 (.126 – .136) 0.889 ± 0.127 (.035 ± .005) RECOMMENDED SOLDER PAD LAYOUT 0.305 ± 0.038 (.0120 ± .0015) TYP 0.50 (.0197) BSC
Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2004 LT/TP 0105 1K REV B • PRINTED IN USA TYPICAL APPLICATIO U RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1990 High Voltage, Gain Selectable Difference Amplifier ±250V Common Mode, Micropower, Pin Selectable Gain = 1, 10 LT1991 Precision Gain Selectable Difference Amplifier Micropower, Pin Selectable Gain = –13 to 14 LT1995 High Speed, Gain Selectable Difference Amplifier 30MHz, 1000V/ µs, Pin Selectable Gain = –7 to 8 LT6010/LT6011/LT6012 Single/Dual/Quad 135 µA 14nV/√Hz Rail-to-Rail Out Similar Op Amp Performance as Precision Op Amp Used in LT1991 Difference Amplifier LT6013/LT6014 Single/Dual 145 µA 8nV/√Hz Rail-to-Rail Out Lower Noise A V ≥ 5 Version of LT1991 Type Op Amp Precision Op Amp LTC6910-X Programmable Gain Amplifiers 3 Gain Configurations, Rail-to-Rail Input and Output Micropower AV = 10 Instrumentation Amplifier Bidirectional Current Source Single Supply AC Coupled Amplifier VM VP VOUT LT1991
1991 TA02
VIN– VIN+ VIN VCC VS = 2.7V TO 36VVS+ VS– LT1991 VOUTLT1991 GAIN = 12 BW = 7Hz TO 32kHz R2* 10k 10k VIN+ – VIN– 10kΩILOAD = *SHORT R2 FOR LOWEST OUTPUT OFFSET CURRENT. INCLUDE R2 FOR HIGHEST OUTPUT IMPEDANCE. 0.1µF 1µF