LT1167 G = 60 TO 4-DIGIT DVM VOLTS INCHES Hg TA01

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1 Features n Singe Gain Set Resistor: G = to, n Gain Error: G =,.8 Max n Input Offset otage Drift:.µ/ C Max n Meets IEC -- Leve ESD Tests with Two Externa k Resistors n Gain Noninearity: G =, Max n Input Offset otage: G =, µ Max n Input Bias Current: pa Max n PSRR at G = : Min n CMRR at G = : 9 Min n Suppy Current:.mA Max n Wide Suppy Range: ±. to ±8 n khz otage Noise: 7.n/ Hz n.hz to Hz Noise:.8µ P-P n Avaiabe in 8-Pin PDIP and SO Packages Appications n Bridge Ampifiers Strain Gauge Ampifiers Thermocoupe Ampifiers Differentia to Singe-Ended Converters Medica Instrumentation L, LT, LTC, LTM, Linear Technoogy and the Linear ogo are registered trademarks of Linear Technoogy Corporation. A other trademarks are the property of their respective owners. LT7 Singe Resistor Gain Programmabe, Precision Instrumentation Ampifier Description The LT 7 is a ow power, precision instrumentation ampifier that requires ony one externa resistor to set gains of to,. The ow votage noise of 7.n/ Hz (at khz) is not compromised by ow power dissipation (.9mA typica for ±. to ± suppies). The part s high accuracy ( maximum noninearity,.8 max gain error (G = )) is not degraded even for oad resistors as ow as k. The LT7 is aser trimmed for very ow input offset votage (µ max), drift (.µ/ C), high CMRR (9, G = ) and PSRR (, G = ). Low input bias currents of pa max are achieved with the use of superbeta processing. The output can hande capacitive oads up to pf in any gain configuration whie the inputs are ESD protected up to k (human body). The LT7 with two externa k resistors passes the IEC -- eve specification. The LT7, offered in 8-pin PDIP and SO packages, requires significanty ess PC board area than discrete muti op amp and resistor designs. The LT7- offers the same performance as the LT7, but its input current characteristic at high common mode votage better supports appications with high input impedance (see the Appications Information section). Typica Appication Singe Suppy Barometer R 9k LTCCZ-. OFFSET R ADJUST k R k R8 k 8 / LT9 S R k / LT9 7 R7 k LUCAS NOA SENOR NPC---A-L k k R SET k k R 8Ω R Ω 8 S LT7 G =. ACCURACY AT C. ACCURACY AT C TO C S = 8 TO 7 OLTS.8.. TO -DIGIT DM INCHES Hg TA NONLINEARITY (/DI) Gain Noninearity OUTPUT OLTAGE (/DI) G = R L = k OUT = ± 7 TA 7fb

2 LT7 Absoute Maximum Ratings (Note ) Suppy otage... ± Differentia Input otage (Within the Suppy otage)...± Input otage (Equa to Suppy otage)... ± Input Current (Note )...±ma Output Short-Circuit Duration... Indefinite Operating Temperature Range... C to 8 C Specified Temperature Range LT7AC/LT7C/ LT7AC-/LT7C- (Note )... C to 7 C LT7AI/LT7I/ LT7AI-/LT7I-... C to 8 C Storage Temperature Range... C to C Lead Temperature (Sodering, sec)... C Pin Configuration R G IN IN S N8 PACKAGE 8-LEAD PDIP TOP IEW 8 7 R G S OUTPUT REF S8 PACKAGE 8-LEAD PLASTIC SO T JMAX = C, θ JA = C/W (N8) T JMAX = C, θ JA = 9 C/W (S8) Order Information LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION SPECIFIED TEMPERATURE RANGE LT7ACN8#PBF LT7ACN8#TRPBF LT7AC 8-Lead PDIP C to 7 C LT7ACS8#PBF LT7ACS8#TRPBF 7A 8-Lead Pastic SO C to 7 C LT7AIN8#PBF LT7AIN8#TRPBF LT7AI 8-Lead PDIP C to 8 C LT7AIS8#PBF LT7AIS8#TRPBF 7AI 8-Lead Pastic SO C to 8 C LT7CN8#PBF LT7CN8#TRPBF LT7C 8-Lead PDIP C to 7 C LT7CS8#PBF LT7CS8#TRPBF 7 8-Lead Pastic SO C to 7 C LT7IN8#PBF LT7IN8#TRPBF LT7I 8-Lead PDIP C to 8 C LT7IS8#PBF LT7IS8#TRPBF 7I 8-Lead Pastic SO C to 8 C LT7CS8-#PBF LT7CS8-#TRPBF 7 8-Lead Pastic SO C to 7 C LT7IS8-#PBF LT7IS8-#TRPBF 7 8-Lead Pastic SO C to 8 C LT7ACS8-#PBF LT7ACS8-#TRPBF 7 8-Lead Pastic SO C to 7 C LT7AIS8-#PBF LT7AIS8-#TRPBF 7 8-Lead Pastic SO C to 8 C LEAD BASED FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION SPECIFIED TEMPERATURE RANGE LT7ACN8 LT7ACN8#TR LT7AC 8-Lead PDIP C to 7 C LT7ACS8 LT7ACS8#TR 7A 8-Lead Pastic SO C to 7 C LT7AIN8 LT7AIN8#TR LT7AI 8-Lead PDIP C to 8 C LT7AIS8 LT7AIS8#TR 7AI 8-Lead Pastic SO C to 8 C LT7CN8 LT7CN8#TR LT7C 8-Lead PDIP C to 7 C LT7CS8 LT7CS8#TR 7 8-Lead Pastic SO C to 7 C LT7IN8 LT7IN8#TR LT7I 8-Lead PDIP C to 8 C LT7IS8 LT7IS8#TR 7I 8-Lead Pastic SO C to 8 C Consut LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a abe on the shipping container. Consut LTC Marketing for information on non-standard ead based finish parts. For more information on ead free part marking, go to: For more information on tape and ree specifications, go to: 7fb

3 Eectrica Characteristics, CM =, T A = C, R L = k, uness otherwise noted. SYMBOL PARAMETER CONDITIONS (NOTE 7) LT7AC/LTC7AI LT7AC-/LTC7AI- LT7C/LTC7I LT7C-/LTC7I- MIN TYP MAX MIN TYP MAX G Gain Range G = (9.k/R G ) k k Gain Error G = G = (Note ) G = (Note ) G = (Note ) Gain Noninearity (Note ) O = ±, G = O = ±, G = and O = ±, G = O = ±, G =, R L = O = ±, G = and, R L = O = ±, G =, R L = OST Tota Input Referred Offset otage OST = OSI OSO /G LT7 OSI Input Offset otage G =, S = ± to ± µ OSO Output Offset otage G =, S = ± to ± µ I OS Input Offset Current 9 pa I B Input Bias Current 8 pa e n Input Noise otage (Note 8).Hz to Hz, G =.Hz to Hz, G =.Hz to Hz, G = and Tota RTI Noise = e ni (e no /G) (Note 8) e ni Input Noise otage Density (Note 8) e no Output Noise otage Density (Note 8) UNITS µ P-P µ P-P µ P-P f O = khz n/ Hz f O = khz (Note ) n/ Hz i n Input Noise Current f O =.Hz to Hz pa P-P Input Noise Current Densty f O = Hz fa/ Hz R IN Input Resistance IN = ± GΩ C IN(DIFF) Differentia Input Capacitance f O = khz.. pf C IN(CM) Common Mode Input Capacitance f O = khz.. pf CM Input otage Range G =, Other Input Grounded S = ±. to ± S = ± to ±8 CMRR Common Mode Rejection Ratio k Source Imbaance, CM = to ± G = G = G = G = PSRR Power Suppy Rejection Ratio S = ±. to ±8 G = G = G = G = S.9 S.9 S. S. S.9 S.9 S. S. I S Suppy Current S = ±. to ± ma OUT Output otage Swing R L = k S = ±. to ± S = ± to ±8 9 S. S. 9 S. S. 8 S. S. 9 S. S. 7fb

4 LT7 Eectrica Characteristics, CM =, T A = C, R L = k, uness otherwise noted. SYMBOL PARAMETER CONDITIONS (NOTE 7) The denotes the specifications which appy over the fu operating temperature range, otherwise specifications are at T A = C., CM =, C T A 7 C, R L = k, uness otherwise noted. LT7AC/LTC7AI LT7AC-/LTC7AI- LT7C/LTC7I LT7C-/LTC7I- MIN TYP MAX MIN TYP MAX I OUT Output Current 7 7 ma BW Bandwidth G = G = G = G = SR Sew Rate G =, OUT = ±.7.7. /µs Setting Time to. Step G = to G = µs µs R REFIN Reference Input Resistance kω I REFIN Reference Input Current REF = µa REF Reference otage Range S. S. S. S. A REF Reference Gain to Output ±. ±. LT7AC/LT7AC- LT7C/LT7C- SYMBOL PARAMETER CONDITIONS (NOTE 7) MIN TYP MAX MIN TYP MAX UNITS Gain Error G = G = (Note ) G = (Note ) G = (Note ) Gain Noninearity OUT = ±, G = OUT = ±, G = and OUT = ±, G =. 8 G/T Gain vs Temperature G < (Note ) / C OST Tota Input Referred OST = OSI OSO /G Offset otage OSI Input Offset otage S = ± to ± 8 8 µ OSIH Input Offset otage Hysteresis (Notes, ).. µ OSO Output Offset otage S = ± to ± 8 7 µ OSOH Output Offset otage Hysteresis (Notes, ) µ OSI /T Input Offset Drift (Note 8) (Note ).... µ/ C OSO /T Output Offset Drift (Note ).7.8 µ/ C I OS Input Offset Current pa I OS /T Input Offset Current Drift.. pa/ C I B Input Bias Current 7 pa I B /T Input Bias Current Drift.. pa/ C CM Input otage Range G =, Other Input Grounded S = ±. to ± S = ± to ±8 CMRR Common Mode Rejection Ratio k Source Imbaance, CM = to ± G = G = G = G = S. S S. S. S. S S. S. 9 UNITS khz khz khz khz 7fb

5 LT7 Eectrica Characteristics The denotes the specifications which appy over the fu operating temperature range, otherwise specifications are at T A = C., CM =, C T A 7 C, R L = k, uness otherwise noted. LT7AC/LT7AC- LT7C/LT7C- SYMBOL PARAMETER CONDITIONS (NOTE 7) MIN TYP MAX MIN TYP MAX UNITS PSRR Power Suppy Rejection Ratio S = ±. to ±8 G = G = G = G = I S Suppy Current S = ±. to ±8.... ma OUT Output otage Swing R L = k S = ±. to ± S = ± to ±8 S. S. S. S. S. S. S. S. I OUT Output Current ma SR Sew Rate G =, OUT = ±.... /µs REF REF otage Range (Note ) S. S. S. S. The denotes the specifications which appy over the fu operating temperature range, otherwise specifications are at T A = C., CM =, C T A 8 C, R L = k, uness otherwise noted. LT7AI/LT7AI- LT7I/LT7I- SYMBOL PARAMETER CONDITIONS (NOTE 7) MIN TYP MAX MIN TYP MAX UNITS Gain Error G = G = (Note ) G = (Note ) G = (Note ) G N Gain Noninearity (Notes, ) O = ±, G = O = ±, G = and O = ±, G = 7 G/T Gain vs Temperature G < (Note ) / C OST Tota Input Referred OST = OSI OSO /G Offset otage OSI Input Offset otage 7 µ OSIH Input Offset otage Hysteresis (Notes, ).. µ OSO Output Offset otage 8 µ OSOH Output Offset otage Hysteresis (Notes, ) µ OSI /T Input Offset Drift (Note 8) (Note ).... µ/ C OSO /T Output Offset Drift (Note ).8 µ/ C I OS Input Offset Current 7 pa I OS /T Input Offset Current Drift.. pa/ C I B Input Bias Current 8 8 pa I B /T Input Bias Current Drift.. pa/ C CM Input otage Range S = ±. to ± S = ± to ±8 CMRR Common Mode Rejection Ratio k Source Imbaance, CM = to ± G = G = G = G = S. S S. S. S. S. 8 9 S. S fb

6 LT7 Eectrica Characteristics The denotes the specifications which appy over the fu operating temperature range, otherwise specifications are at T A = C., CM =, C T A 7 C, R L = k, uness otherwise noted. SYMBOL PARAMETER CONDITIONS (NOTE 7) PSRR Power Suppy Rejection Ratio S = ±. to ±8 G = G = G = G = LT7AI/LT7AI- LT7I/LT7I- MIN TYP MAX MIN TYP MAX I S Suppy Current.... ma OUT Output otage Swing S = ±. to ± S = ± to ±8 8 S. S. S. S. 9 S. S. S. S. I OUT Output Current ma SR Sew Rate G =, OUT = ± /µs REF REF otage Range (Note ) S. S. S. S. UNITS Note : Stresses beyond those isted under Absoute Maximum Ratings may cause permanent damage to the device. Exposure to any Absoute Maximum Rating condition for extended periods may affect device reiabiity and ifetime. Note : Does not incude the effect of the externa gain resistor RG. Note : This parameter is not tested. Note : The LT7AC/LT7C/LT7AC-/LT7C- are designed, characterized and expected to meet the industria temperature imits, but are not tested at C and 8 C. I-grade parts are guaranteed. Note : This parameter is measured in a high speed automatic tester that does not measure the therma effects with onger time constants. The magnitude of these therma effects are dependent on the package used, heat sinking and air fow conditions. Note : Hysteresis in offset votage is created by package stress that differs depending on whether the IC was previousy at a higher or ower temperature. Offset votage hysteresis is aways measured at C, but the IC is cyced to 8 C I-grade (or 7 C C-grade) or C I-grade ( C C-grade) before successive measurement. of the parts wi pass the typica imit on the data sheet. Note 7: Typica parameters are defined as the of the yied parameter distribution. Note 8: Referred to input. 7fb

7 Typica Performance Characteristics LT7 Gain Noninearity, G = Gain Noninearity, G = Gain Noninearity, G = NONLINEARITY (/DI) NONLINEARITY (/DI) NONLINEARITY (/DI) G = OUTPUT OLTAGE (/DI) R L = k OUT = ± 7 G G = OUTPUT OLTAGE (/DI) R L = k OUT = ± 7 G G = OUTPUT OLTAGE (/DI) R L = k OUT = ± 7 G NONLINEARITY (/DI) Gain Noninearity, G = G = OUTPUT OLTAGE (/DI) R L = k OUT = ± 7 G NONLINEARITY () 8 7 Gain Noninearity vs Temperature OUT = TO R L = k G = G =, G = 7 TEMPERATURE ( C) GAIN ERROR () Gain Error vs Temperature OUT = ± R L = k *DOES NOT INCLUDE TEMPERATURE EFFECTS OF R G G = G = * G = * G = * 7 TEMPERATURE ( C) 7 G 7 G PERCENT OF UNITS () Distribution of Input Offset otage, T A = C G = 7 N8 ( LOTS) S8 ( LOTS) TOTAL PARTS PERCENT OF UNITS () Distribution of Input Offset otage, T A = C G = 7 N8 ( LOTS) S8 ( LOTS) TOTAL PARTS PERCENT OF UNITS () Distribution of Input Offset otage, T A = 8 C G = 7 N8 ( LOTS) S8 ( LOTS) TOTAL PARTS 8 INPUT OFFSET OLTAGE (µ) INPUT OFFSET OLTAGE (µ) 8 INPUT OFFSET OLTAGE (µ) 7 G 7 G 7 G 7fb 7

8 LT7 Typica Performance Characteristics PERCENT OF UNITS () Distribution of Output Offset otage, T A = C 7 N8 ( LOTS) S8 ( LOTS) TOTAL PARTS G = PERCENT OF UNITS () Distribution of Output Offset otage, T A = C 7 N8 ( LOTS) S8 ( LOTS) TOTAL PARTS G = PERCENT OF UNITS () Distribution of Output Offset otage, T A = 8 C 7 N8 ( LOTS) S8 ( LOTS) TOTAL PARTS G = OUTPUT OFFSET OLTAGE (µ) OUTPUT OFFSET OLTAGE (µ) OUTPUT OFFSET OLTAGE (µ) 7 G 7 G 7 G PERCENT OF UNITS () Distribution of Input Offset otage Drift T A = C TO 8 C G = 7 N8 ( LOTS) S8 ( LOTS) TOTAL PARTS PERCENT OF UNITS () Distribution of Output Offset otage Drift T A = C TO 8 C G = 7 N8 ( LOTS) S8 ( LOTS) TOTAL PARTS CHANGE IN OFFSET OLTAGE (µ) 8 Warm-Up Drift T A = C G = S8 N INPUT OFFSET OLTAGE DRIFT (µ/ C) OUTPUT OFFSET OLTAGE DRIFT (µ/ C) TIME AFTER POWER ON (MINUTES) 7 G 7 G7 7 G9 PERCENT OF UNITS () Input Bias Current T A = C 7 S8 N8 9 TOTAL PARTS PERCENT OF UNITS () Input Offset Current T A = C 7 S8 N8 9 TOTAL PARTS INPUT BIAS AND OFFSET CURRENT (pa) Input Bias and Offset Current vs Temperature CM = I OS I B INPUT BIAS CURRENT (pa) INPUT OFFSET CURRENT (pa) 7 7 TEMPERATURE ( C) 7 G 7 G 7 G 8 7fb

9 Typica Performance Characteristics LT7 INPUT BIAS CURRENT (pa) Input Bias Current vs Common Mode Input otage 8 C C C 7 C C 9 9 COMMON MODE INPUT OLTAGE () 7 G COMMON MODE REJECTION RATIO () 8 Common Mode Rejection Ratio vs Frequency. G = G = G = G = T A = C k SOURCE IMBALANCE k k FREQUENCY (Hz) k 7 G NEGATIE POWER SUPPLY REJECTION RATIO () 8 Negative Power Suppy Rejection Ratio vs Frequency. G = G = G = = T A = C G = k k FREQUENCY (Hz) k 7 G POSITIE POWER SUPPLY REJECTION RATIO () 8 Positive Power Suppy Rejection Ratio vs Frequency Gain vs Frequency Suppy Current vs Suppy otage. G = G = G = = T A = C G = k k FREQUENCY (Hz) k 7 G GAIN () G = G = G = G = T A = C.. FREQUENCY (khz) 7 G7 SUPPLY CURRENT (ma) SUPPLY OLTAGE () 8 C C C 7 G8 OLTAGE NOISE DENSITY (n Hz) otage Noise Density vs Frequency T A = C /f CORNER = Hz /f CORNER = 9Hz GAIN = GAIN = /f CORNER = 7Hz GAIN =, BW LIMIT GAIN = k k k FREQUENCY (Hz) 7 G9 NOISE OLTAGE (µ/di).hz to Hz Noise otage, G = T A = C TIME (SEC) 7 G NOISE OLTAGE (.µ/di).hz to Hz Noise otage, Referred to Input, G = T A = C TIME (SEC) 7 G 7fb 9

10 LT7 Typica Performance Characteristics CURRENT NOISE DENSITY (fa/ Hz) OERSHOOT () Current Noise Density vs Frequency.Hz to Hz Current Noise Short-Circuit Current vs Time R S T A = C FREQUENCY (Hz) 7 G CURRENT NOISE (pa/di) T A = C TIME (SEC) Overshoot vs Capacitive Load Large-Signa Transient Response Sma-Signa Transient Response OUT = ±m R L = A = A = A CAPACITIE LOAD (pf) 7 G /DI G = R L = k C L = pf µs/di 7 G 7 G8 OUTPUT CURRENT (ma) (SINK) (SOURCE) T A = C T A = C T A = C T A = 8 C T A = 8 C T A = C TIME FROM OUTPUT SHORT TO GROUND (MINUTES) m/di G = R L = k C L = pf µs/di 7 G 7 G9 OUTPUT IMPEDANCE (Ω) Output Impedance vs Frequency Large-Signa Transient Response Sma-Signa Transient Response T A = C G = TO /DI m/di. FREQUENCY (khz) G = R L = k C L = pf µs/di 7 G G = R L = k C L = pf µs/di 7 G 7 G 7fb

11 Typica Performance Characteristics LT7 PEAK-TO-PEAK OUTPUT SWING () Undistorted Output Swing vs Frequency Large-Signa Transient Response Sma-Signa Transient Response G =,, G = T A = C FREQUENCY (khz) 7 G7 /DI G = R L = k C L = pf µs/di 7 G m/di G = R L = k C L = pf µs/di 7 G Setting Time vs Gain Large-Signa Transient Response Sma-Signa Transient Response T A = C OUT = m =. SETTLING TIME (µs) /DI m/di GAIN () G = R L = k C L = pf µs/di 7 G7 G = R L = k C L = pf µs/di 7 G8 7 G OUTPUT STEP () 8 8 Setting Time vs Step Size S = ± G = T A = C C L = pf R L = k TO. TO. TO. OUT OUT TO SETTLING TIME (µs) SLEW RATE (/µs) Sew Rate vs Temperature OUT = ± G =.8 SLEW SLEW 7 TEMPERATURE ( C) OUTPUT OLTAGE SWING () (REFERRED TO SUPPLY OLTAGE) S S. S. S. S. S. S. S. S. Output otage Swing vs Load Current 8 C C C SOURCE SINK S.. OUTPUT CURRENT (ma) 7 G 7 G 7 G9 7fb

12 LT7 Bock Diagram IN R Ω Q B A R.7k C R k A R k OUTPUT R G R G 8 IN R Ω B A C R7 k R8 k Q R.7k REF 7 PREAMP STAGE DIFFERENCE AMPLIFIER STAGE 7 F Figure. Bock Diagram Theory Of Operation The LT7 is a modified version of the three op amp instrumentation ampifier. Laser trimming and monoithic construction aow tight matching and tracking of circuit parameters over the specified temperature range. Refer to the bock diagram (Figure ) to understand the foowing circuit description. The coector currents in Q and Q are trimmed to minimize offset votage drift, thus assuring a high eve of performance. R and R are trimmed to an absoute vaue of.7k to assure that the gain can be set accuratey (. at G = ) with ony one externa resistor R G. The vaue of R G determines the transconductance of the preamp stage. As R G is reduced for arger programmed gains, the transconductance of the input preamp stage increases to that of the input transistors Q and Q. This increases the open-oop gain when the programmed gain is increased, reducing the input referred gain reated errors and noise. The input votage noise at gains greater than is determined ony by Q and Q. At ower gains the noise of the difference ampifier and preamp gain setting resistors increase the noise. The gain bandwidth product is determined by C, C and the preamp transconductance which increases with programmed gain. Therefore, the bandwidth does not drop proportionay to gain. The input transistors Q and Q offer exceent matching, which is inherent in NPN bipoar transistors, as we as picoampere input bias current due to superbeta processing. The coector currents in Q and Q are hed constant due to the feedback through the Q-A-R oop and Q-A-R oop which in turn impresses the differentia input votage across the externa gain set resistor R G. Since the current that fows through R G aso fows through R and R, the ratios provide a gained-up differentia votage, G = (R R)/R G, to the unity-gain difference ampifier A. The common mode votage is removed by A, resuting in a singe-ended output votage referenced to the votage on the REF pin. The resuting gain equation is: OUT REF = G( IN IN ) where: G = (9.kΩ/R G ) soving for the gain set resistor gives: R G = 9.kΩ/(G ) 7fb

13 Theory of Operation Input and Output Offset otage The offset votage of the LT7 has two components: the output offset and the input offset. The tota offset votage referred to the input (RTI) is found by dividing the output offset by the programmed gain (G) and adding it to the input offset. At high gains the input offset votage dominates, whereas at ow gains the output offset votage dominates. The tota offset votage is: Tota input offset votage (RTI) = input offset (output offset/g) Tota output offset votage (RTO) = (input offset G) output offset Reference Termina The reference termina is one end of one of the four k resistors around the difference ampifier. The output votage of the LT7 (Pin ) is referenced to the votage on the reference termina (Pin ). Resistance in series with the REF pin must be minimized for best common mode rejection. For exampe, a Ω resistance from the REF pin to ground wi not ony increase the gain error by. but wi ower the CMRR to 8. Singe Suppy Operation For singe suppy operation, the REF pin can be at the same potentia as the negative suppy (Pin ) provided the output of the instrumentation ampifier remains inside the specified operating range and that one of the inputs is at east. above ground. The barometer appication on the front page of this data sheet is an exampe that satisfies these conditions. The resistance R b from the bridge transducer to ground sets the operating current for the bridge and aso has the effect of raising the input common mode votage. The output of the LT7 is aways inside the specified range since the barometric pressure rarey goes ow enough to cause the output to rai (. inches of Hg corresponds to.). For appications that require the output to swing at or beow the REF potentia, the votage on the REF pin can be eve shifted. An op amp is used to buffer the votage on the REF pin since a parasitic series resistance wi degrade the CMRR. The appication in the back of this data sheet, Four Digit Pressure Sensor, is an exampe. LT7 Output Offset Trimming The LT7 is aser trimmed for ow offset votage so that no externa offset trimming is required for most appications. In the event that the offset needs to be adjusted, the circuit in Figure is an exampe of an optiona offset adjust circuit. The op amp buffer provides a ow impedance to the REF pin where resistance must be kept to minimum for best CMRR and owest gain error. IN IN R G 8 LT7 REF ±m ADJUSTMENT RANGE OUTPUT / LT k m Ω Ω m Figure. Optiona Trimming of Output Offset otage 7 F Input Bias Current Return Path The ow input bias current of the LT7 (pa) and the high input impedance (GΩ) aow the use of high impedance sources without introducing additiona offset votage errors, even when the fu common mode range is required. However, a path must be provided for the input bias currents of both inputs when a purey differentia signa is being ampified. Without this path the inputs wi foat to either rai and exceed the input common mode range of the LT7, resuting in a saturated input stage. Figure shows three exampes of an input bias current path. The first exampe is of a purey differentia signa source with a kω input current path to ground. Since the impedance of the signa source is ow, ony one resistor is needed. Two matching resistors are needed for higher impedance signa sources as shown in the second exampe. Baancing the input impedance improves both common mode rejection and DC offset. The need for input resistors is eiminated if a center tap is present as shown in the third exampe. 7fb

14 LT7 Theory of Operation THERMOCOUPLE MICROPHONE, R G LT7 HYDROPHONE, R G LT7 R G ETC LT7 k k k CENTER-TAP PROIDES BIAS CURRENT RETURN 7 F Figure. Providing an Input Common Mode Current Path Appications Information The LT7 is a ow power precision instrumentation ampifier that requires ony one externa resistor to accuratey set the gain anywhere from to. The output can hande capacitive oads up to pf in any gain configuration and the inputs are protected against ESD strikes up to k (human body). Input Current at High Common Mode otage When operating within the specified input common mode range, both the LT7 and LT7- operate as shown in the Input Bias Current vs Common Mode Input otage graph shown in the Typica Performance Characteristics. If however the inputs are within approximatey.8 of the positive suppy, the LT7 input current wi increase to approximatey µa to µa. If the impedance of the circuit driving the LT7 inputs is sufficienty high (e.g., MΩ when S = ), this increased input current can pu the input votage sufficienty high to keep the eevated input current fowing. The LT7- has been modified so that the input current is typicay two orders of magnitude ower under simiar conditions. The LT7- is recommended for new designs where input impedance is high. Input Protection The LT7 can safey hande up to ±ma of input current in an overoad condition. Adding an externa k input resistor in series with each input aows DC input faut votages up to ± and improves the ESD immunity to 8k (contact) and k (air discharge), which is the IEC -- eve specification. If ower vaue input resistors are needed, a camp diode from the positive suppy to each input wi maintain the IEC -- specification to eve for both air and contact discharge. A N9 drain/source to gate is a good ow eakage diode for use with k resistors, see Figure. The input resistors shoud be carbon and not meta fim or carbon fim. R IN CC J N9 CC J N9 R G R IN OPTIONAL FOR HIGHEST ESD PROTECTION CC LT7 EE Figure. Input Protection REF OUT 7 F RFI Reduction In many industria and data acquisition appications, instrumentation ampifiers are used to accuratey ampify sma signas in the presence of arge common mode votages or high eves of noise. Typicay, the sources of these very sma signas (on the order of microvots or miivots) are sensors that can be a significant distance from the signa conditioning circuit. Athough these sensors may be connected to signa conditioning circuitry, using shieded or unshieded twisted-pair cabing, the cabing may act as antennae, conveying very high frequency interference directy into the input stage of the LT7. 7fb

15 LT7 Appications Information The ampitude and frequency of the interference can have an adverse effect on an instrumentation ampifier s input stage by causing an unwanted DC shift in the ampifier s input offset votage. This we known effect is caed RFI rectification and is produced when out-of-band interference is couped (inductivey, capacitivey or via radiation) and rectified by the instrumentation ampifier s input transistors. These transistors act as high frequency signa detectors, in the same way diodes were used as RF enveope detectors in eary radio designs. Regardess of the type of interference or the method by which it is couped into the circuit, an out-of-band error signa appears in series with the instrumentation ampifier s inputs. To significanty reduce the effect of these out-of-band signas on the input offset votage of instrumentation ampifiers, simpe owpass fiters can be used at the inputs. These fiters shoud be ocated very cose to the input pins of the circuit. An effective fiter configuration is iustrated in Figure, where three capacitors have been added to the inputs of the LT7. Capacitors C XCM and C XCM form owpass fiters with the externa series resistors R S, to any out-of-band signa appearing on each of the input traces. Capacitor C XD forms a fiter to reduce any unwanted signa that woud appear across the input traces. An added benefit to using C XD is that the circuit s AC common mode rejection is not degraded due to common mode capacitive IN IN R S C XCM.k.µF R S.k C XD.µF C XCM.µF EXTERNAL RFI FILTER R G LT7 f Hz OUT 7 F Figure. Adding a Simpe RC Fiter at the Inputs to an Instrumentation Ampifier Is Effective in Reducing Rectification of High Frequency Out-of-Band Signas imbaance. The differentia mode and common mode time constants associated with the capacitors are: t DM(LPF) = ()(R S )(C XD ) t CM(LPF) = (R S, )(C XCM, ) Setting the time constants requires a knowedge of the frequency, or frequencies of the interference. Once this frequency is known, the common mode time constants can be set foowed by the differentia mode time constant. To avoid any possibiity of inadvertenty affecting the signa to be processed, set the common mode time constant an order of magnitude (or more) arger than the differentia mode time constant. Set the common mode time constants such that they do not degrade the LT7 s inherent AC CMR. Then the differentia mode time constant can be set for the bandwidth required for the appication. Setting the differentia mode time constant cose to the sensor s BW aso minimizes any noise pickup aong the eads. To avoid any possibiity of common mode to differentia mode signa conversion, match the common mode time constants to or better. If the sensor is an RTD or a resistive strain gauge, then the series resistors R S, can be omitted, if the sensor is in proximity to the instrumentation ampifier. Ro Your Own Discrete vs Monoithic LT7 Error Budget Anaysis The LT7 offers performance superior to that of ro your own three op amp discrete designs. A typica appication that ampifies and buffers a bridge transducer s differentia output is shown in Figure. The ampifier, with its gain set to, ampifies a differentia, fu-scae output votage of m over the industria temperature range. To make the comparison chaenging, the ow cost version of the LT7 wi be compared to a discrete instrumentation amp made with the A grade of one of the best precision quad op amps, the LTA. The LT7C outperforms the discrete ampifier that has ower OS, ower I B and comparabe OS drift. The error budget comparison in Tabe shows how various errors are cacuated and how each error affects the tota error budget. The tabe shows the greatest differences between the discrete soution and 7fb

16 LT7 Appications Information / LTA Ω Ω Ω Ω R G 99Ω k* k* LT7C REF Ω** k** k** / LTA PRECISION BRIDGE TRANSDUCER LT7 MONOLITHIC INSTRUMENTATION AMPLIFIER G =, R G = ± TC SUPPLY CURRENT =.ma MAX Figure. Ro Your Own vs LT7 / LTA k* k* ROLL YOUR OWN INST AMP, G = *. RESISTOR MATCH, / C TRACKING ** DISCRETE RESISTOR, ±/ C TC TRACKING SUPPLY CURRENT =.ma FOR AMPLIFIERS 7 F Tabe. Ro Your Own vs LT7 Error Budget ERROR SOURCE Absoute Accuracy at T A = C Input Offset otage, µ Output Offset otage, µ Input Offset Current, na CMR, Drift to 8 C Gain Drift, / C Input Offset otage Drift, µ/ C Output Offset otage Drift, µ/ C Resoution Gain Noninearity, of Fu Scae Typ.Hz to Hz otage Noise, µ P-P G =, S = ± A errors are min/max and referred to input. LT7C CIRCUIT CALCULATION µ/m (µ/)/m [(pa)(/)ω]/m [(.)()]/m ( )( C) [(.µ/ C)( C)]/m [(µ/ C)( C)]//m.8µ P-P /m the LT7 are input offset votage and CMRR. Note that for the discrete soution, the noise votage specification is mutipied by which is the RMS sum of the uncoreated noise of the two input ampifiers. Each of the ampifier errors is referenced to a fu-scae bridge differentia votage of m. The common mode range of the bridge is. The LT data sheet provides offset votage, offset votage drift and offset current specifications for the matched op amp pairs used in the error-budget tabe. Even with an exceent matched op amp ike the LT, the discrete soution s tota error is significanty higher than the LT7 s ROLL YOUR OWN CIRCUIT CALCULATION µ/m [(µ)()/]/m [(pa)(ω)/]/m [(. Match)()]/m Tota Absoute Error (/ C Track)( C) [(.µ/ C)( C)]/m [(.µ/ C)()( C)]//m Tota Drift Error (.µ P-P )( )/m Tota Resoution Error Grand Tota Error ERROR, OF FULL SCALE LT7C ROLL YOUR OWN tota error. The LT7 has additiona advantages over the discrete design, incuding ower component cost and smaer size. Current Source Figure 7 shows a simpe, accurate, ow power programmabe current source. The differentia votage across Pins and is mirrored across R G. The votage across R G is ampified and appied across R X, defining the output current. The µa bias current fowing from Pin is buffered by the LT JFET operationa ampifier. This 7fb

17 Appications Information IN IN R G 8 I L = X = R X 9.kΩ G = R G LT7 S S 7 [(IN) (IN)]G R X REF / LT R X X LOAD Figure 7. Precision otage-to-current Converter I L 7 F7 has the effect of improving the resoution of the current source to pa, which is the maximum I B of the LTA. Repacing R G with a programmabe resistor greaty increases the range of avaiabe output currents. Nerve Impuse Ampifier The LT7 s ow current noise makes it idea for high source impedance EMG monitors. Demonstrating the LT7 s abiity to ampify ow eve signas, the circuit in Figure 8 takes advantage of the ampifier s high gain and ow noise operation. This circuit ampifies the ow eve nerve impuse signas received from a patient at Pins and. R G and the parae combination of R and R set a gain of ten. The potentia on LT s Pin creates a ground for the common mode signa. C was chosen to maintain the stabiity of the patient ground. The LT7 s LT7 high CMRR ensures that the desired differentia signa is ampified and unwanted common mode signas are attenuated. Since the DC portion of the signa is not important, R and C make up a.hz highpass fiter. The AC signa at LT s Pin is ampified by a gain of set by (R7/R8). The parae combination of C and R7 form a owpass fiter that decreases this gain at frequencies above khz. The abiity to operate at ± on.9ma of suppy current makes the LT7 idea for battery-powered appications. Tota suppy current for this appication is.7ma. Proper safeguards, such as isoation, must be added to this circuit to protect the patient from possibe harm. Low I B Favors High Impedance Bridges, Lowers Dissipation The LT7 s ow suppy current, ow suppy votage operation and ow input bias currents optimize it for battery-powered appications. Low overa power dissipation necessitates using higher impedance bridges. The singe suppy pressure monitor appication (Figure 9) shows the LT7 connected to the differentia output of a.k bridge. The bridge s impedance is amost an order of magnitude higher than that of the bridge used in the error-budget tabe. The picoampere input bias currents keep the error caused by offset current to a negigibe eve. The LT eve shifts the LT7 s reference pin and the ADC s anaog ground pins above ground. The LT7 s and LT s combined power dissipation is sti ess than the bridge s. This circuit s tota suppy current is just.8ma. IN PATIENT GROUND IN PATIENT/CIRCUIT PROTECTION/ISOLATION C.µF R M R k / LT R k R k R G k 8 A = POLE AT khz 7 LT7 G =.Hz HIGHPASS C.7µF 8 R M R8 Ω / LT C nf 7 R7 k OUTPUT /m 7 F8 Figure 8. Nerve Impuse Ampifier 7fb 7

18 LT7 Appications Information BI TECHNOLOGIES 7-8- RKQ (. RATIO MATCH).k.k.k.k G = 9Ω 8 7 LT7 k k k / LT REF IN ADC LTC 8 AGND DIGITAL DATA OUTPUT 7 F9 Figure 9. Singe Suppy Bridge Ampifier Typica Appication AC Couped Instrumentation Ampifier IN IN R G LT7 8 REF C R.µF k OUTPUT / LT f = (π)(r)(c) =.Hz 7 TA 8 7fb

19 Package Description N8 Package 8-Lead PDIP (Narrow. Inch) (Reference LTC DWG # -8-) LT7.* (.) MAX 8 7. ±.* (.77 ±.8).. (7. 8.).. (..). ±. (. ±.7).8. (..8) ( ). (.) TYP. (.) BSC NOTE: INCHES. DIMENSIONS ARE MILLIMETERS *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED. INCH (.mm). (.8) MIN.8 ±. (.7 ±.7). (.8) MIN N8 7fb 9

20 LT7 Package Description S8 Package 8-Lead Pastic Sma Outine (Narrow. Inch) (Reference LTC DWG # -8-). BSC. ± (.8.) NOTE 8 7. MIN. ±..8. (.79.97)..7 (.8.988) NOTE. ±. TYP RECOMMENDED SOLDER PAD LAYOUT.8. (..).. (..8) 8 TYP..9 (..7).. (..).. (..7) NOTE: INCHES. DIMENSIONS IN (MILLIMETERS)..9 (..8) TYP. DRAWING NOT TO SCALE. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED." (.mm). (.7) BSC SO8 7fb

21 LT7 Revision History (Revision history begins at Rev B) RE DATE DESCRIPTION PAGE NUMBER B / Added LT7- to Description, Absoute Maximum Ratings, Order Information, Eectrica Characteristics and -, Appications Information Section Information furnished by Linear Technoogy Corporation is beieved to be accurate and reiabe. However, no responsibiity is assumed for its use. Linear Technoogy Corporation makes no representation that the interconnection of its circuits as described herein wi not infringe on existing patent rights. 7fb

22 LT7 Typica Appication -Digit Pressure Sensor 9 R8 9k LTCCZ-. / LT R9 k. ACCURACY AT ROOM TEMP. ACCURACY AT C TO C OLTS.8.. INCHES Hg 8... LUCAS NOA SENOR NPC--A-L k k R 8Ω R k k Ω 8 R SET R k / LT R k 9 LT7 G = 7 TO -DIGIT DM 9 R k / LT CALIBRATION ADJUST R k C µf 8 R7 8k 7 TA Reated Parts PART NUMBER DESCRIPTION COMMENTS LTC Precision Chopper-Stabiized Instrumentation Ampifier Best DC Accuracy LT Precision, Micropower, Singe Suppy Instrumentation Ampifier Fixed Gain of or, I S < µa LT High Speed, JFET Instrumentation Ampifier Fixed Gain of or, /µs Sew Rate LT8 Low Power, Singe Resistor Programmabe Instrumentation Ampifier I SUPPLY = µa Max LTC8 -Bit, Low Power, ksps ADC with Seria and Parae I/O Singe Suppy or ± Operation, ±.LSB INL and ±LSB DNL Max LT Precision Series Reference Micropower;.,, ersions; High Precision LT8 -Bit Accurate Op Amp, Low Noise Fast Setting -Bit Accuracy at Low and High Frequencies, 9MHz GBW, /µs, 9ns Setting LTC Active RC Fiter Lowpass, Bandpass, Highpass Responses; Low Noise, Low Distortion, Four nd Order Fiter Sections LTC -Bit, ksps, Samping ADC Singe Suppy, Bipoar Input Range: ±, Power Dissipation: mw Typ LT RE B PRINTED IN USA Linear Technoogy Corporation McCarthy Bvd., Mipitas, CA 9-77 (8) -9 FAX: (8) -7 LINEAR TECHNOLOGY CORPORATION 998 7fb