FEATURES APPLICATIO S TYPICAL APPLICATIO. LT1996 Precision, 100µA Gain Selectable Amplifier DESCRIPTIO

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1 FEATURES Pin Configurable as a Difference Amplifier, Inverting and Noninverting Amplifier Difference Amplifier Gain Range to CMRR >db Noninverting Amplifier Gain Range. to Inverting Amplifier Gain Range. to Gain Error: <.% Gain Drift: < ppm/ C Wide Supply Range: Single.V to Split ±V Micropower Operation: µa Supply Input Offset Voltage: µv (Max) Gain Bandwidth Product: khz Rail-to-Rail Output Space Saving -Lead MSOP and DFN Packages APPLIC S U 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. LT Precision, µa Gain Selectable Amplifier DESCRIPTIO U The LT combines a precision operational amplifier with eight precision resistors to form a one-chip solution for accurately amplifying voltages. Gains from to with a gain accuracy of.% 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 db. The amplifier features a µv maximum input offset voltage and a gain bandwidth product of khz. The device operates from any supply voltage from.v to V and draws only µa supply current on a V supply. The output swings to within mv of either supply rail. The internal resistors have excellent matching characteristics; variation is.% over temperature with a guaranteed matching temperature coefficent of less than ppm/ C. The resistors are also extremely stable over voltage, exhibiting a nonlinearity of less than ppm. The LT is fully specified at V and ±V supplies and from C to C. The device is available in space saving -lead MSOP and DFN packages. For an amplifier with selectable gains from to, see the LT data sheet. TYPICAL APPLIC U Rail-to-Rail Gain = Difference Amplifier Distribution of Resistor Matching V M(IN) V P(IN) INPUT RANGE ±V R IN = kω k/ k/ k/ k/ k/ k/ pf pf V V k k LT V = V SWING mv TO EITHER RAIL TA PERCENTAGE OF UNITS (%). LTA G =.. RESISTOR MATCHING (%). TAb f

2 LT ABSOLUTE AXI U RATI GS W W W Total Supply Voltage (V to V )... V Input Voltage (Pins P/M, Note )... ±V Input Current (Pins P/M/P/M, Note )... ±ma Output Short-Circuit Duration (Note )... Indefinite Operating Temperature Range (Note )... C to C Specified Temperature Range (Note )... C to C U (Note ) Maximum Junction Temperature DD Package... C MS Package... C Storage Temperature Range DD Package... C to C MS Package... C to C MSOPLead Temperature (Soldering, sec)... C U PACKAGE/ORDER I FOR W U P P P V TOP VIEW M M M OUT DD PACKAGE -LEAD (mm mm) PLASTIC DFN T JMAX = C, θ JA = C/W UNDERSIDE METAL CONNECTED TO V (PCB CONNECTION OPTIONAL) ORDER PART NUMBER LTCDD LTIDD LTACDD LTAIDD DD PART MARKING* LBPC P P P V TOP VIEW MS PACKAGE -LEAD PLASTIC MSOP T JMAX = C, θ JA = C/W M M M OUT ORDER PART NUMBER LTCMS LTIMS LTACMS LTAIMS MS PART MARKING* LTBPB *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 The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T A = C. Difference amplifier configuration, = V, V or ±V; V CM = V = half supply, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS G Gain Error = ±V, = ±V; R L = k G = ; LTAMS ±. ±. % G = ; LTAMS ±. ±. % G = ; LTAMS ±. ±. % G = ; LTADD ±. ±. % G = ; LTADD ±. ±. % G = ; LTADD ±. ±. % G = ; LT ±. ±. % G = ; LT ±. ±. % G = ; LT ±. ±. % GNL Gain Nonlinearity = ±V; = ±V; R L = k; G = ppm G/ T Gain Drift vs Temperature (Note ) = ±V; = ±V; R L = k. ppm/ C CMRR Common Mode Rejection Ratio, = ±V; G = ; V CM = ±.V Referred to Inputs (RTI) LTAMS db LTADD db LT db = ±V; G = ; V CM =.V to.v LTAMS db LTADD db LT db f

3 ELECTRICAL CHARACTERISTICS LT The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T A = C. Difference amplifier configuration, = V, V or ±V; V CM = V = half supply, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS CMRR Common Mode Rejection Ratio (RTI) = ±V; G = ; V CM =.V to.v LTAMS db LTADD db LT db V CM Input Voltage Range (Note ) P/M Inputs = ±V; V = V.. V = V, V; V =.V.. V = V, V; V =.V.. V P/M Inputs, P/M Connected to = ±V; V = V V = V, V; V =.V.. V = V, V; V =.V.. V P/M Inputs = ±V; V = V.. V = V, V; V =.V.. V = V, V; V =.V. V P/M Inputs = ±V; V = V.. V = V, V; V =.V.. V = V, V; V =.V. V V OS Op Amp Offset Voltage (Note ) LTAMS, = V, µv µv LTAMS, = ± µv µv LTMS µv µv LTDD µv µv V OS / T Op Amp Offset Voltage Drift (Note ). µv/ C I B Op Amp Input Bias Current. na. na I OS Op Amp Input Offset Current LTA pa pa LT pa pa Op Amp Input Noise Voltage.Hz to Hz. µv P-P.Hz to Hz. µv RMS.Hz to Hz. µv P-P.Hz to Hz. µv RMS e n Input Noise Voltage Density G = ; f = khz nv/ Hz (Includes Resistor Noise) G = ; f = khz nv/ Hz R IN Input Impedance (Note ) P (M = Ground) kω P (M = Ground).. kω P (M = Ground).. kω M (P = Ground) kω M (P = Ground)... kω M (P = Ground)... kω f

4 LT ELECTRICAL CHARACTERISTICS The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T A = C. Difference amplifier configuration, = V, V or ±V; V CM = V = half supply, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS R Resistor Matching (Note ) G = ; LTAMS ±. ±. % G = ; LTAMS ±. ±. % G = ; LTAMS ±. ±. % G = ; LTADD ±. ±. % G = ; LTADD ±. ±. % G = ; LTADD ±. ±. % G = ; LT ±. ±. % G = ; LT ±. ±. % G = ; LT ±. ±. % R/ T Resistor Temperature Coefficient (Note ) Resistor Matching. ppm/ C Absolute Value ppm/ C PSRR Power Supply Rejection Ratio = ±.V to ±V (Note ) db Minimum Supply Voltage.. V Output Voltage Swing (to Either Rail) No Load = V, V mv = V, V mv = ±V mv ma Load = V, mv = V, V mv = ±V mv I SC Output Short-Circuit Current (Sourcing) Drive Output Positive; ma Short Output to Ground ma Output Short-Circuit Current (Sinking) Drive Output Negative; ma Short Output to or Midsupply ma BW db Bandwidth G = khz G = khz G = khz GBWP Op Amp Gain Bandwidth Product f = khz khz t r, t f Rise Time, Fall Time G = ;.tep; % to % µs G = ;.tep; % to % µs t S Settling Time to.% G = ; = V, V; tep µs G = ; = V, V; tep µs G = ; = ±V; tep µs G = ; = ±V; tep µs SR Slew Rate = V, V; = V to V.. V/µs = ±V; = ±V.. V/µs I S Supply Current = V, V µa µa = ±V µa µa Note : Absolute Maximum Ratings are those beyond which the life of the device may be impaired. Note : The P/M and P/M 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 ma. The P/M inputs can withstand ±V if P/M are grounded and = ±V (see Applications Information section about High Voltage CM Difference Amplifiers ). Note : A heat sink may be required to keep the junction temperature below absolute maximum ratings. f

5 LT ELECTRICAL CHARACTERISTICS Note : Both the LTC and LTI are guaranteed functional over the C to C temperature range. Note : The LTC is guaranteed to meet the specified performance from C to C and is designed, characterized and expected to meet specified performance from C to C but is not tested or QA sampled at these temperatures. The LTI is guaranteed to meet specified performance from C to C. Note : This parameter is not % tested. Note : Input voltage range is guaranteed by the CMRR test at = ±V. For the other voltages, this parameter is guaranteed by design and through correlation with the ±V test. See the Applications Information section to determine the valid input voltage range under various operating conditions. Note : 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 = V OS Noise Gain I OS k I B k ( R P /R N ) where R P and R N are the total resistance at the op amp positive and negative terminal respectively. Note : Resistors connected to the minus inputs. Resistor matching is not tested directly, but is guaranteed by the gain error test. Note : Input impedance is tested by a combination of direct measurements and correlation to the CMRR and gain error tests. TYPICAL PERFOR A CE CHARACTERISTICS U W (Difference Amplifier Configuration) SUPPLY CURRENT (µa) Supply Current vs Supply Voltage T A = C T A = C T A = C OUTPUT VOLTAGE SWING (mv) Output Voltage Swing vs Temperature = V, V NO LOAD OUTPUT LOW (LEFT AXIS) OUTPUT HIGH (RIGHT AXIS) OUTPUT VOLTAGE (mv) Output Voltage Swing vs Load Current (Output Low) = V, V T A = C T A = C T A = C SUPPLY VOLTAGE (±V) V TEMPERATURE ( C) V LOAD CURRENT (ma) G G G OUTPUT VOLTAGE SWING (mv) Output Voltage Swing vs Load Current (Output High) = V, V T A = C T A = C T A = C LOAD CURRENT (ma) G OUTPUT SHORT-CIRCUIT CURRENT (ma) Output Short-Circuit Current vs Temperature = V, V SOURCING SINKING TEMPERATURE ( C) G INPUT OFFSET VOLTAGE (µv) Input Offset Voltage vs Difference Gain = V, V REPRESENTATIVE PARTS GAIN (V/V) G f

6 LT TYPICAL PERFOR A CE CHARACTERISTICS U W (Difference Amplifier Configuration) OUTPUT OFFSET VOLTAGE (mv) Output Offset Voltage vs Difference Gain Gain Error vs Load Current Slew Rate vs Temperature = V, V REPRESENTATIVE PARTS. GAIN (V/V) GAIN ERROR (%) GAIN = = ±V = ±V T A = C REPRESENTATIVE UNITS LOAD CURRENT (ma) SLEW RATE (V/µs) GAIN = = ±V = ±V SR (FALLING EDGE) SR (RISING EDGE) TEMPERATURE ( C) G G G db BANDWIDTH (khz) Bandwidth vs Gain CMRR vs Frequency PSRR vs Frequency = V, V T A = C GAIN (V/V) G CMRR (db) GAIN = GAIN = GAIN = = V, V T A = C k k k M FREQUENCY (Hz) G PSRR (db) = V, V T A = C GAIN = GAIN = GAIN = k k k FREQUENCY (Hz) G OUTPUT IMPEDANCE (Ω). Output Impedance vs Frequency CMRR vs Temperature Gain Error vs Temperature = V, V T A = C GAIN = GAIN = GAIN = CMRR (db) GAIN = = ±V GAIN ERROR (%) GAIN = = ±V. k k k FREQUENCY (Hz) REPRESENTATIVE UNITS TEMPERATURE ( C) REPRESENTATIVE UNITS TEMPERATURE ( C) G G G f

7 LT TYPICAL PERFOR A CE CHARACTERISTICS U W (Difference Amplifier Configuration) GAIN (db) Gain vs Frequency GAIN = GAIN = GAIN = = V, V TA = C. FREQUENCY (khz) G GAIN (db). Gain and Phase vs Frequency PHASE (RIGHT AXIS) GAIN (LEFT AXIS) = V, V TA = C GAIN = FREQUENCY (khz) G PHASE (deg) OP AMP VOLTAGE NOISE (nv/div).hz to Hz Voltage Noise = ±V T A = C MEASURED IN G = ERRED TO OP AMP INPUTS TIME (s) G Small Signal Transient Response, Gain = Small Signal Transient Response, Gain = Small Signal Transient Response, Gain = mv/div mv/div mv/div µs/div G µs/div G µs/div G PI FU CTIO S U U U (Difference Amplifier Configuration) P (Pin ): Noninverting Gain-of- input. Connects a k internal resistor to the op amp s noninverting input. P (Pin ): Noninverting Gain-of- input. Connects a (k/) internal resistor to the op amp s noninverting input. P (Pin ): Noninverting Gain-of- input. Connects a (k/) internal resistor to the op amp s noninverting input. V (Pin ): Negative Power Supply. Can be either ground (in single supply applications), or a negative voltage (in split supply applications). (Pin ): Reference Input. Sets the output level when difference between inputs is zero. Connects a k internal resistor to the op amp s noninverting input. OUT (Pin ): Output. = V (V P V M ) (V P V M ) (V P V M ). (Pin ): Positive Power Supply. Can be anything from.v to V above the V voltage. M (Pin ): Inverting Gain-of- input. Connects a (k/) internal resistor to the op amp s inverting input. M (Pin ): Inverting Gain-of- input. Connects a (k/) internal resistor to the op amp s inverting input. M (Pin ): Inverting Gain-of- input. Connects a k internal resistor to the op amp s inverting input. f

8 LT BLOCK DIAGRA W M M M k/ k OUT k/ pf k/ k/ k/ OUT LT k/ pf k P P P V BD APPLIC S I FOR Introduction The LT 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 LT 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 LT is a precision device with µv typical offset voltage and na 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.v of and V of V. 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 mv of the supply rails. The gain bandwidth product of the op amp is about khz. In noise gains of or more, it is stable into capacitive loads up to pf. In noise gains below, it is stable into capacitive loads up to pf. The Resistors The resistors internal to the LT are very well matched SiChrome based elements protected with barrier metal. Although their absolute tolerance is fairly poor (±%), their matching is to within.%. This allows the chip to achieve a CMRR of db, and gain errors within.%. The resistor values are (k/), (k/), (k/) and k, connected to each of the inputs. The resistors have power limitations of watt for the k and (k/) resistors,.watt for the (k/) resistors and.watt for the (k/) resistors; however, in practice, power dissipation will be limited well below these values by the f

9 LT APPLIC S I FOR maximum voltage allowed on the input and pins. The k resistors connected to the M and P inputs are isolated from the substrate, and can therefore be taken beyond the supply voltages. The naming of the pins P, P, P, etc., is based on their admittances relative to the feedback and admittances. Because it has times the admittance, the voltage applied to the P input has times the effect of the voltage applied to the input. Bandwidth The bandwidth of the LT 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, the db bandwidth is limited to khz, with peaking of about db at khz. In the highest configurable gains, bandwidth is limited to khz. Input Noise The LT input noise is comprised of the Johnson noise of the internal resistors ( ktr), and the input voltage noise of the op amp. Paralleling all four resistors to the input gives a.kω resistance, for nv/ Hz of voltage noise. The equivalent network on the input gives another nv/ Hz, and the op amp nv/ Hz. Taking their RMS sum gives a total nv/ Hz input referred noise floor. Output noise depends on configuration and noise gain. Input Resistance The LT 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 GΩ impedance. In the classical noninverting op amp configuration, the LT presents the high input impedance of the op amp, as is usual for the noninverting case. Common Mode Input Voltage Range The LT valid common mode input range is limited by three factors:. Maximum allowed voltage on the pins. The input voltage range of the internal op amp. Valid output voltage The maximum voltage allowed on the P, M, P and M 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 V. If more than ma is allowed to flow through these pins, there is a risk that the LT will be detrimmed or damaged. The P and M 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 P and M pins is ±V. The input voltage range of the internal op amp extends to within.v of and V of V. 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 P, P, P and. (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 mv 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. f

10 LT APPLIC S I FOR Consider Figure. This shows the LT configured as a gain of difference amplifier on a single supply with k/ k/ V k pf V EXT R G R G T R F V R F V F Figure. Difference Amplifier Cannot Produce V on a Single Supply. Provide a Negative Supply, or Raise Pin, or Provide µv of V DM the output connected to ground. This is a great circuit, but it does not support V DM = V at any common mode because the output clips into ground while trying to produce. It can be fixed simply by declaring the valid input differential range not to extend below.mv, or by elevating the pin above mv, or by providing a negative supply. Calculating Input Voltage Range Figure shows the LT in the generalized case of a difference amplifier, with the inputs shorted for the common mode calculation. The values of R F and R G are dictated by how the P inputs and pin are connected. By superposition we can write: T = V EXT (R F /(R F R G )) V (R G /(R F R G )) Or, solving for V EXT : V EXT = T ( R G /R F ) V R G /R F But valid T voltages are limited to.v and V V, so: MAX V EXT = (.) ( R G /R F ) V R G /R F and: MIN V EXT = (V ) ( R G /R F ) V R G /R F V CM.V V DM V k/ k/ k/ k/ pf k F LT = V DM Figure. 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 ( and, above). In most cases, the inverting inputs M through M 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. Note that, with V MORE V EXT MAX OR MIN R G R G T Figure. Calculating Additional Voltage Range of Inverting Inputs V MORE =, the op amp output is at V. From the max V EXT (the high cm limit), as V MORE goes positive, the op amp output will go more negative from V by the amount V MORE R F /R G, so: = V V MORE R F /R G Or: V MORE = (V ) R G /R F The most negative that can go is V.V, so: Max V MORE = (V V.V) R G /R F (should be positive) The situation where this function is negative, and therefore problematic, when V = and V =, has already been dealt with in Figure. The strength of the equation is demonstrated in that it provides the three solutions R F V R F V F f

11 LT APPLIC S I FOR suggested in Figure : raise V, lower V, or provide some negative V MORE. Likewise, from the lower common mode extreme, making the negative input more negative will raise the output voltage, limited by.v. MIN V MORE = (V.V) R G /R F (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 shows the textbook R G = GAIN GAIN = R F /R G CLASSICAL NONINVERTING OP AMP CONFIGURN. YOU PROVIDE THE RESISTORS. k/ k/ k/ k/ k/ k/ R F k k pf pf LT CLASSICAL NONINVERTING OP AMP CONFIGURN IMPLEMENTED WITH LT. R F = k, R G =.k, GAIN =.. representation of the circuit on the top. The LT is shown on the bottom configured in a precision gain of.. One of the benefits of the noninverting op amp configuration is that the input impedance is extremely high. The LT maintains this benefit. Given the finite number of available feedback resistors in the LT, the number of gain configurations is also finite. The complete list of such Hi-Z input noninverting gain configurations is shown in Table. Many of these are also represented in Figure 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. Configuring the M Pins for Simple Noninverting Gains. The P Inputs are driven as shown in the examples on the next page M, M, M Connection Gain M M M Output Output Output. Output Output Grounded. Output Float Grounded. Output Grounded Output. Float Output Grounded. Output Grounded Float. Output Grounded Grounded. Grounded Output Output. Float Grounded Output. Grounded Output Float. Grounded Output Grounded. Grounded Float Output Float Float Grounded. Grounded Grounded Output Float Grounded Float Float Grounded Grounded Grounded Float Float Grounded Float Grounded Grounded Grounded Float Grounded Grounded Grounded GAIN IS ACHIEVED BY GROUNDING, FLOATING OR FDING BACK THE AVAILABLE RESISTORS TO ARRIVE AT DESIRED R F AND R G. WE PROVIDE YOU WITH <.% RESISTORS. F Figure. The LT as a Classical Noninverting Op Amp f

12 LT APPLIC S I FOR M M M P P P LT OUT M M M P P P LT OUT M M M P P P LT OUT GAIN = GAIN = GAIN =. M M M P P P LT OUT M M M P P P LT OUT M M M P P P LT OUT GAIN = GAIN = GAIN =. M M M P P P LT OUT M M M P P P LT OUT M M M P P P LT OUT GAIN =. GAIN = GAIN = M M M P P P LT OUT M M M P P P LT OUT GAIN = GAIN = F Figure. Some Implementations of Classical Noninverting Gains Using the LT. High Input Z Is Maintained f

13 LT APPLIC S I FOR 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 LT resistors are ready at hand. The four precision resistors can provide several attenuation levels, and these are tabulated in Table as a design reference. R A R G T OKAY UP TO ±V T = A A = R G /(R A R G ) CLASSICAL ATTENUATOR k/ k/ k/ Figure. LT Provides for Easy Attenuation to the Op Amp s Input. The P 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 unique gains between. and, as plotted in Figure. 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 and, and seeking the best match. Average gain resolution is.%, with worst case steps of about % as seen in Figure. GAIN... Figure. Over Unique Gain Settings Achievable with the LT by Combining Attenuation with Noninverting Gain T k LT ATTENUATING TO THE INPUT BY DRIVING AND GROUNDING AND FLOATING INPUTS R A = k, R G = k/, SO A =.. COUNT F LT F Table. Configuring the P Pins for Various Attenuations. Those Shown in Bold Are Functional Even When the Input Drive Exceeds the Supplies P, P, P, Connection A P P P. Grounded Grounded Grounded Driven. Grounded Grounded Float Driven. Grounded Float Grounded Driven. Grounded Float Float Driven. Float Grounded Grounded Driven. Float Grounded Float Driven. Grounded Grounded Driven Grounded. Grounded Grounded Driven Float. Grounded Grounded Driven Driven. Grounded Float Driven Grounded. Grounded Float Driven Float. Grounded Float Driven Driven. Grounded Driven Grounded Grounded. Grounded Driven Grounded Float. Grounded Driven Grounded Driven. Float Grounded Driven Grounded. Grounded Driven Float Grounded. Float Grounded Driven Float. Grounded Driven Float Float. Grounded Driven Float Driven. Float Grounded Driven Driven. Grounded Driven Driven Grounded. Grounded Driven Driven Float. Grounded Driven Driven Driven. Driven Grounded Grounded Grounded. Driven Grounded Grounded Float. Driven Grounded Grounded Driven. Float Driven Grounded Grounded. Driven Grounded Float Grounded. Float Driven Grounded Float. Driven Grounded Float Driven. Float Driven Grounded Driven. Driven Grounded Driven Grounded. Driven Grounded Driven Float. Driven Grounded Driven Driven. Driven Float Grounded Grounded. Float Float Driven Grounded. Driven Float Grounded Driven. Driven Driven Grounded Grounded. Driven Driven Grounded Float. Driven Driven Grounded Driven. Float Driven Float Grounded. Float Driven Driven Grounded. Driven Float Float Grounded. Driven Float Driven Grounded. Driven Driven Float Grounded. Driven Driven Driven Grounded f

14 LT APPLIC S I FOR Inverting Configuration The inverting amplifier, shown in Figure, is another classical op amp configuration. The circuit is actually identical to the noninverting amplifier of Figure, except that and GND have been swapped. The list of available gains is shown in Table, and some of the circuits are shown in Figure. Noise gain is 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. (DRIVE) R G R F pf = GAIN GAIN = R F /R G CLASSICAL INVERTING OP AMP CONFIGURN. YOU PROVIDE THE RESISTORS. k/ k/ k Table. Configuring the M Pins for Simple Inverting Gains M, M, M Connection Gain M M M. Output Output Drive. Output Float Drive. Output Drive Output. Float Output Drive. Output Drive Float. Output Drive Drive. Drive Output Output. Float Drive Output. Drive Output Float. Drive Output Drive. Drive Float Output Float Float Drive. Drive Drive Output Float Drive Float Float Drive Drive Drive Float Float Drive Float Drive Drive Drive Float Drive Drive Drive k/ k/ k/ pf k/ k LT CLASSICAL INVERTING OP AMP CONFIGURN IMPLEMENTED WITH LT. R F = k, R G =.k, GAIN =.. GAIN IS ACHIEVED BY GROUNDING, FLOATING OR FDING BACK THE AVAILABLE RESISTORS TO ARRIVE AT DESIRED R F AND R G. WE PROVIDE YOU WITH <.% RESISTORS. F Figure. The LT as a Classical Inverting Op Amp. Note the Circuit Is Identical to the Noninverting Amplifier, Except that and Ground Have Been Swapped f

15 LT APPLIC S I FOR M M M P P P LT OUT M M M P P P LT OUT M M M P P P LT OUT GAIN =. GAIN = GAIN =. M M M P P P LT OUT M M M P P P LT OUT M M M P P P LT OUT GAIN = GAIN = GAIN =. M M M P P P LT OUT M M M P P P LT OUT M M M P P P LT OUT GAIN =. GAIN = GAIN = M M M P P P LT OUT M M M P P P LT OUT GAIN = GAIN = F Figure. It Is Simple to Get Precision Inverting Gains with the LT. Input Impedance Varies from.kω (Gain = ) to kω (Gain = ) f

16 LT APPLIC S I FOR Difference Amplifiers The resistors in the LT allow it to easily make difference amplifiers also. Figure shows the basic -resistor difference amplifier and the LT. A difference gain of is shown, but notice the effect of the additional dashed connections. By connecting the k resistors in parallel, the gain is reduced by a factor of. Of course, with so many resistors, there are many possible gains. Table shows the difference gains and how they are achieved. Note that, as for inverting amplifiers, the noise gain is more than the signal gain. Table. Connections Giving Difference Gains for the LT Gain V IN V IN Output GND (). P M M, M P, P. P M M P. P M M, M P, P. P M M P. P M M P. P, P M, M M P. P M M, M P, P. P M M P. P M M P. P, P M, M M P. P M M P P M. P, P M, M M P P M P, P M, M P M P, P M, M P, P M, M P, P, P M, M, M PARALLEL TO CHANGE R F, R G R G R G pf pf Figure. Difference Amplifier Using the LT. Gain Is Set Simply by Connecting the Correct Resistors or Combinations of Resistors. Gain of Is Shown, with Dashed Lines Modifying It to Gain of.. Noise Gain Is Optimal R F = GAIN ( ) GAIN = R F /R G CLASSICAL DIFFERENCE AMPLIFIER USING THE LT k/ k/ k/ k/ k/ k/ k k LT CLASSICAL DIFFERENCE AMPLIFIER IMPLEMENTED WITH LT. R F = k, R G =.k, GAIN =. ADDING THE DASHED CONNECTIONS CONNECTS THE TWO k RESISTOR IN PARALLEL, SO R F IS REDUCED TO k. GAIN BECOMES k/.k =.. R F F f

17 LT APPLIC S I FOR M M M P P P LT OUT M M M P P P LT OUT M M M P P P LT OUT GAIN =. GAIN = GAIN =. M M M P P P LT OUT M M M P P P LT OUT M M M P P P LT OUT GAIN = GAIN = GAIN =. M M M P P P LT OUT M M M P P P LT OUT M M M P P P LT OUT GAIN =. GAIN = GAIN = M M M P P P LT OUT M M M P P P LT OUT GAIN = GAIN = F Figure. Many Difference Gains Are Achievable Just by Strapping the Pins f

18 LT APPLIC S I FOR k/ k R F CROSS- R G COUPLING V R OUT G = GAIN ( V IN ) R F GAIN = R F /R G k/ k/ k/ k/ k/ pf pf k LT CLASSICAL DIFFERENCE AMPLIFIER CLASSICAL DIFFERENCE AMPLIFIER IMPLEMENTED WITH LT. R F = k, R G =.k, GAIN =. GAIN CAN BE ADJUSTED BY "CROSS COUPLING." MAKING THE DASHED CONNECTIONS REDUCE THE GAIN FROM T. WHEN CROSS COUPLING, S WHAT IS CONNECTED TO THE V IN VOLTAGE. CONNECTING P AND M GIVES =. CONNECTIONS TO V IN ARE SYMMETRIC: M AND P. F Figure. Another Method of Selecting Difference Gain Is Cross-Coupling. The Additional Method Means the LT Provides Extra Integer Gains Difference Amplifier: Additional Integer Gains Using Cross-Coupling Figure shows the basic difference amplifier as well as the LT in a difference gain of. 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 to. Using this method, additional integer gains are achievable, as shown in Table below. Note that the equations can be written by inspection from the V IN connections, and that the V IN connections are simply the opposite (swap P for M and M for P). The method is the same as for the LT, except that the LT applies a multiplier of. Noise gain, bandwidth, and input impedance specifications for the various cases are also tabulated, as these are not obvious. Schematics are provided in Figure. Table. Connections Using Cross-Coupling. Note That Equations Can Be Written by Inspection of the Column Gain Noise db BW R IN R IN Gain Equation Gain khz Typ kω Typ kω M M M P P P M M M P P P M M M P P P LT OUT GAIN = GAIN = LT OUT GAIN = LT OUT M M M P P P M M M P P P M M M P P P LT OUT LT OUT GAIN = LT OUT P, M M, P P, M, M M, P, P GAIN = GAIN = F P, M M, P P, P, M M, M, P P, M M, P Figure. Integer Gain Difference Amplifiers Using Cross-Coupling P, P, M M, M, P f

19 LT APPLIC S I FOR High Voltage CM Difference Amplifiers This class of difference amplifier remains to be discussed. Figure shows the basic circuit on the top. The effective input voltage range of the circuit is extended by the fact that resistors R T attenuate the common mode voltage seen by the op amp inputs. For the LT, the most useful resistors for R G are the M and P kω 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, T. By superposition we can write: T = V EXT (R F R T )/(R G R F R T ) V (R G R T )/ (R F R G R T ) V TERM (R F R G )/(R T R F R G ) Solving for V EXT : V EXT = ( R G /(R F R T )) (T V (R G R T )/ (R F R G R T ) V TERM (R F R G )/(R T R F R G )) Given the values of the resistors in the LT, this equation has been simplified and evaluated, and the resulting equations provided in Table. As before, substituting. and V for V LIM will give the valid upper and lower common mode extremes respectively. Following are sample calculations for the case shown in Figure, right-hand side. Note that P and M are terminated so row of Table provides the equation: MAX V EXT = / (.V) V / V TERM = (.) (.).(.) () =.V and: MIN V EXT = / (V V) V / V TERM = (.)().(.) () =.V but this exceeds the V absolute maximum rating of the P, M pins, so V becomes the de facto negative common mode limit. Several more examples of high CM circuits are shown in Figures,, for various supplies. Table. HighV CM Connections Giving Difference Gains for the LT Max, Min V EXT Noise (Substitute., Gain V IN V IN R T Gain V for V LIM ) P M / V LIM - V / P M P, M / V LIM V / V TERM P M P, M / V LIM V / V TERM P M P P / V LIM V / V TERM M M (= V EXT ) V INPUT CM RANGE = V TO.V R G R G R T R T pf pf Figure. Extending CM Input Range R F V R F = GAIN ( ) GAIN = R F /R G V TERM HIGH CM VOLTAGE DIFFERENCE AMPLIFIER INPUT CM TO OP AMP IS ATTENUATED BY RESISTORS R T CONNECTED TO V TERM. k/ k/ k/ k/ k/ k/ V k k V LT HIGH NEGATIVE CM VOLTAGE DIFFERENCE AMPLIFIER IMPLEMENTED WITH LT. R F = k, R G = k, R T.k, GAIN = V TERM = V = = V, V =.V, V = V..V F f

20 LT APPLIC S I FOR M M M P P P V LT OUT V.V M M M P P P V LT OUT M M M P P P V LT OUT V V CM =.V TO.V V CM =.V TO V V DM > mv V CM =.V TO.V V DM <mv M M M P P P V LT OUT V.V M M M P P P V LT OUT V.V V M M M P P P V LT OUT V.V.V V CM =.V TO.V V CM = V TO.V V CM = V TO.V M M M P P P V LT OUT V.V M M M P P P V LT OUT V.V V M M M P P P V LT OUT V.V.V V CM =.V TO.V V CM =.V TO V V CM = V TO.V M M M P P P V LT OUT V.V M M M P P P V LT OUT V.V V M M M P P P V LT OUT V.V.V V CM = V TO.V V CM =.V TO.V V CM = V TO.V F Figure. Common Mode Ranges for Various LT Difference Amp Configurations on = V, V, with Gain = f

21 LT APPLIC S I FOR M M M P P P V LT OUT V.V M M M P P P V V M V M CC V IN M LT OUT LT OUT V IN P P P V V CM =.V TO.V V CM =.V TO.V V DM > mv V CM =.V TO.V V DM <mv M M M P P P V LT OUT V.V M M M P P P V LT OUT V.V V M M M P P P V LT OUT V.V.V V CM =.V TO.V V CM =.V TO.V V CM =.V TO.V M M M P P P V LT OUT V.V M M M P P P V LT OUT V.V V M M M P P P V LT OUT V.V.V V CM =.V TO.V V CM =.V TO.V V CM =.V TO.V M M M P P P V LT OUT V.V M M M P P P V LT OUT V.V V M M M P P P V LT OUT V.V.V V CM =.V TO.V V CM =.V TO.V V CM =.V TO.V F Figure. Common Mode Ranges for Various LT Difference Amp Configurations on = V, V, with Gain = f

22 LT APPLIC S I FOR M M M P P P V LT OUT V V CM =.V TO.V M M M P P P V LT OUT V M M M P P P V LT OUT V V V CM = V TO.V V CM =.V TO.V V DM > mv V DM <mv M M M P P P V LT OUT M M M P P P V LT OUT V M M M P P P V LT OUT.V V V CM =.V TO.V V V CM =.V TO.V V V CM =.V TO.V M M M P P P V LT OUT M M M P P P V LT OUT V M M M P P P V LT OUT V V V V CM =.V TO.V V CM =.V TO V V CM = V TO.V M M M P P P V LT OUT M M M P P P V LT OUT V M M M P P P V LT OUT V V V CM =.V TO.V V CM =.V TO V V CM = V TO.V F Figure. Common Mode Ranges for Various LT Difference Amp Configurations on = ±V, with Gain = f

23 LT PACKAGE DESCRIPTIO U DD Package -Lead Plastic DFN (mm mm) (Reference LTC DWG # --). ±. R =. TYP. ±.. ±.. ±.. ±. ( SIDES). ±.. BSC. ±. ( SIDES) PACKAGE OUTLINE RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS PIN TOP MARK (S NOTE ).. ±. ( SIDES). ±.... ±. ( SIDES) NOTE:. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M- VARIN OF (WD-). CHECK THE LTC WEBSITE DATA SHT FOR CURRENT STATUS OF VARIN ASSIGNMENT. DRAWING NOT TO SCALE. ALL DIMENSIONS ARE IN MILLIMETERS. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCD.mm ON ANY SIDE. EXPOSED PAD SHALL BE SOLDER PLATED. SHADED AREA IS ONLY A ERENCE FOR PIN LOCN ON THE TOP AND BOTTOM OF PACKAGE. ±. ( SIDES) BOTTOM VIEW EXPOSED PAD (DD) DFN. ±.. BSC. ±. (. ±.). ±. (. ±.) (NOTE ). ±. (. ±.). (.) MIN. ±. (. ±.) TYP.. (..). (.) BSC RECOMMENDED SOLDER PAD LAYOUT GAUGE PLANE. (.). (.) DETAIL A DETAIL A NOTE:. DIMENSIONS IN MILLIMETER/(INCH). DRAWING NOT TO SCALE. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCD.mm (.") PER SIDE. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCD.mm (.") PER SIDE. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE.mm (.") MAX TYP. ±. (. ±.) SEATING PLANE. ±. (. ±.). (.) MAX.. (..) TYP. (.) BSC. ±. (. ±.) (NOTE ). (.). ±. (. ±.) MSOP (MS) 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. f

24 LT TYPICAL APPLIC U Micropower A V = Instrumentation Amplifier V M / LT k/ k/ pf k V P k/ / LT k/ k/ k/ pf k LT TA Bidirectional Controlled Current Source AC Coupled Amplifier Differential Input/Output G = Amplifier M M M P P P LT R k ( ) I LOAD = kω.µf M M M P P P LT GAIN = BW = Hz TO khz M M M P P P LT USE V OCM TO SET THE DESIRED OUTPUT COMMON MODE LEVEL k k LT V OCM TA RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT High Voltage Difference Amplifier ±V Input Common Mode, Micropower, Pin Selectable Gain =, LT Precision, µa Gain Selectable Amplifier Gain Resistors of k, k, k LT MHz, V/µs Gain Selectable Amplifier High Speed, Pin Selectable Gain = to LT/LT/LT Single/Dual/Quad Precision Op Amp Similar Performance as LT Diff Amp, µa, nv Hz, Rail-to-Rail Out LT/LT Single/Dual Precision Op Amp Lower Noise A V Version of LT, µa, nv/ Hz, Rail-to-Rail Out LTC-X Programmable Gain Amplifiers Gain Configurations, Rail-to-Rail Input and Output LT/TP K PRINTED IN USA Linear Technology Corporation McCarthy Blvd., Milpitas, CA - () - FAX: () - LINEAR TECHNOLOGY CORPORN f