ANALOG DEVICES REF43: 2.5 V Low Power Precision Voltage Reference Data Sheet (Rev D 2004-08-01-) handbook
Contents
1. 4859C maximum quiescent current the REF 43 is ideally suited to Storage Temperature Range 65 to 175 applications where power dissipation must be minimized as in Junction Temperature Range 65 C to 175 precision battery powered equipment The low supply current Lead Temperature Soldering 10 sec 300 C minimizes drift due to self heating after power up A temperature output provides a means of determining system PACKAGE TYPE 64 Note 2 Sic UNITS ambient temperature Applications of the REF 43 include A D 8 Pin Hermetic DIP 2 148 CAN and D A conversion 4 20mA transmitter receiver operation log 8 Pin Plastic DIP P 103 a CN amplifiers and power supply regulators 8 Pin SO S 458 13 CN For a low cost 2 5V reference available in small outline pack NOTES ages consult the REF 03 data sheet ABSOLUTE MAXIMUM RATINGS dad D Supply Voltage Output Short Circuit Duration 40V Indefinite 1 Absolute maximum ratings apply to both DICE and packaged parts unless otherwise noted is specified for worst case mounting conditions i e is specified for device in socket for TO CerDIP P DIP and LCC packages is specified for device soldered to printed circuit board for SO package m ELECTRICAL CHARACTERISTICS at Vj 5V I OmA 25 C unless otherwise noted REF 43F REF 43G PARAMETER SYMBOL CONDITIONS MIN TYP MAX2. 16mA Output Ratio ATopEgRATING 4TopeRATING As an example assume the transmitter is to operate over the 50 C to 150 C temperature range 16mA 16mA 0 08mA C 150 C 50 C 200 Output Ratio If l ourin the ice water bath equaled 6 3mA then in the boiling water bath 100 lour o c 100 C 0 08mA C 6 3mA 14 3 REV With the REF 43 in the boiling water bath the gain trim in 16mA OUT this example should be adjusted so equals 14 3mA 200 20 50 C 4mA 9 6mA Once the gain trim has been completed the offset trim can be made Remember that adjusting the offsettrim will notaffect Table 1 shows the values of R6 and R7 required for various the gain temperature ranges The offset trim can be set at any known temperature by TABLE 1 adjusting RS until the output current equals TEMP R6 R7 Al RANGE FIXED TRIMPOT lout s Tmin 4mA 0 C to 70 C 10k 5k E ee 40 C to 85 C 6k 3k Using the previous example and assuming the REF 43 is at 50 C to 150 C 3k Ok 20 C FIGURE 11 Temperature to 4 20mA Transmitter y BY TO 404 QP Yaet B OFFSET TRIM ALL RESISTORS 1 4W 5 UNLESS OTHERWISE NOTED FIGURE 12 Low Power Logarithmic Amplifier 15 7 KI Your REF 43 GND Your S Vout Vi FOR Viy gt OV TEL LABS 1381 LOW POWER LOGAR
3. Range REF43FZ 10ppm C 8 Pin Hermetic DIP 40 C to 85 C REF43GZ 25ppm C 8 Pin Hermetic DIP 40 C to 85 C REF43GP 25ppm C 8 Pin Plastic DIP 40 C to 85 C REF43GS 25ppm C 8 Pin SOIC 40 C to 85 C REF43GS REEL 25ppm C 8 Pin SOIC 409 to 85 C REF43GS REEL7 25ppm C 8 Pin SOIC 40 C to 85 C REF43GSZ 25ppm C 8 Pin SOIC 409 to 85 C REF43GSZ REEL7 25ppm C 8 Pin SOIC 40 C to 85 C REF43NBC Z Pb free part SIMPLIFIED SCHEMATIC REV D o GROUND Information furnished by Analog Devices is believed to be accurate and reliable However no responsibility is assumed by Analog Devices for its use norfor any infringements of patents or other rights ofthird parties that may result from its use No license is granted by implication or otherwise One Technology Way P O Box 9106 Norwood MA 02062 9106 U S A under any patent or patent rights of Analog Devices Trademarks and Tel 781 329 4700 www analog com registered trademarks are the property of their respective owners Fax 781 326 8703 2004 Analog Devices Inc All rights reserved REF43 The REF 43 may be operated with supply voltages from 4 5V Operating Temperature Range to 40V The output voltage changes by less than 1784V from REF 43F 2 40 C to 485 C one extreme of supply voltage to the other With only 450uA REF 43G 3 2 P 5 40 1
4. VOUT SENSEF PADS 4A AND 4B MUST BOTH BE BONDED TO GROUND VOUT FORCE AND SENSE ARE TYPICALLY BONDED TOGETHER AT THE LOAD DIE SIZE 0 085 x 0 062 inch 5270 sq mils 2 16 x 1 57 mm 3 39 sq mm WAFER TEST LIMITS at Va 5V T 25 C unless otherwise noted REF 43N PARAMETER __ CONDITIONS UNITS Cutput Vollage Tolerance 1 Dici S i Line Regulation mM Vira l to 40V MEE 2 ppm MAX Load Regulation 00000 OMA to mA BEEN ppm MAX Quiescent Supply Current lax T No Load LLL 450 sl Load Current Sourcing _ I a 10 m NOTES Final output trims are not performed on standard product dice These trims are typically pertormed after packaging Precision Monolithics Imc assumes no responsibility for improper trimming by t e customer Contact factory for trim methods 2 Guaranteed by load regulation test Electrical tests are performed at walter probe to the limits shown Due to variations in assembly methods anc normal yield loss yield after packaging ia not guaranteed for standard product dice Consult factory to negotiate specifications based on dice lot qualification through sample lot assembly and testing TYPICAL PERFORMANCE CHARACTERISTICS LOAD REGULATION LINE REGULATION OUTPUT VOLTAGE CHANGE vs TEMPERATURE vs TEMPERATURE vs
5. power corresponds to a die temperature increase of 60 C above ambient Die temperature is calculated by T Pp X 6 4 where Pp is the sum of the power dissipation due to quiescent current and current delivered to the load Pp Isy X Vg Loan Vs 2 5V The for different packages in a PC board surrounded by free air are listed below REV FIGURE 4 2 5V Reference PACKAGE TYPE CERDIP 80 PLASTIC 80 An additional source of error is dueto temperature gradients across the package leads resulting in thermocouple effects Temperature gradients will be generated when the IC is required to dissipate large amounts of power Even at low power levels thermocouple effects may appear as low fre quency noise due to air currents across the leads A signifi cant improvement in low frequency noise will be found by encasing the reference and any metal junctions such as solder joints which form thermocouples along the refer ence path in a light insulating foam or other enclosure to reduce turbulence Thermocouple effects can easily add over 10uVp p of low frequency noise The temperature output of the REF 43 provides an output voltage which is proportional to the die temperature When the REF 43 is operating at constant load current this is a good indication of system temperature The nominal output voltage at 25 C is 56 7mV and the slope is typically 1 9mV C 0 2mV C The TEMP output
6. ANALOG 2 5 V Low Power Precision DEVICES Voltage Reference FEATURES PIN CONFIGURATION e 42 5 Volt Output 30 10 Low Temperature Coefficient 25ppm C Max 8 PIN CERDIP Excellent Regulation Z Suffix Load Regulation 20ppm mA Max 8 PIN PLASTIC DIP Line Regulation Max P Suffix Supply Current 45004 8 PIN SO Temperature Voltage 1 9 S Suffix Operating Voltage Range 4 5V lo 40V RESERVED FOR FACTORY TESTING amp Extended Industrial Temp Range mo 40 C to 485 C MAKE NO ELECTRICAL CONNECTION TO THESE PINS Available in Die Form GENERAL DESCRIPTION Tight output tolerances and low thermal drift are assured by The REF43 is a low power precision reference providing a zener zap trimming of both output voltage and its temperature stable 2 5 V output independent of variations in supply voltage coefficient A unique curvature correction circuit reduces the load conditions or ambient temperature It is suitable as a thermal curvature which 1s characteristic of many previous reference level for 8 10 and 12 bit data acquisition systems bandgap references or wherever a stable known voltage is required ORDERING GUIDE Number of Initial Temperature Package Package Part per Temperature Model Accuracy Coefficient Description Option Reel Tray
7. CAL CHARACTERISTICS at Viy 5V OmA 40 C T a s 485 C for the REF 43F G unless otherwise noted REF 43F HEF 43G PARAMETER SYMBOL CONDITIONS MIN TYP MAX MIN MAX UNITS Quiput Volt puns Ne Load 0 06 02 Of 202 Tolerance Output Voltage Mo Load 2497 2500 2 503 2 495 2 500 2 505 V Output co Tee NDS TERES 7 B ppm C igi 9 a C s Ta s 485 C 10 10 25 PP Coefficient Mote 1 Vin 4 5 Line Regulat 1 d 1 d mV ine Regulation ip 40V Load Regul 20 35 25 40 egulabon to 10 E GOuiescent 400 600 400 600 Supply Current ur a Lone m Load Current i or 10 o 10 20 Sourcing L Temperatura Hysteresis of AT 225 C 100 100 py Output Voltage Temperature Voltage TCVTEMP 1 8 1 9 Output Tempco HOTES 1 Output voltage temperature coefficient is measured by the box method The tempcois defined as the slope ofthe diagonal of a box drawn around ihe output voltage plotted against temperatura Vo jris measured at Tuin 25 C and Ty Tor tne applicable temperature range The lowest af these three readings is subtracted from the highest reading and the resulting difference divided by Tuag 2 Guaranteed by Load Regulation test BURN IN CIRCUIT OUTPUT VOLTAGE TRIM METHOD REV D _3 REF43 DICE CHARACTERISTICS VIN TEMPERATURE OUT GROUND GROUND TRIM VOUT FO2 VIN 6B
8. EED AND HIGHER LINEARITY IS REQUIRED FIGURE 7 Precision Current Source 8 TO FIGURE 8 Single Supply Kelvin OQutput Thermometer Fou 10 200 34511 TRIM FOR Your 2 98V AT 25 K 273 REV D FIGURE 9 Thermocouple Amplifier with Cold Junction Compensation ISOTHERMAL BLOCK COLD JUNCTION COMPENSATION TEMPERATURE MEASUREMENT Using the REF 43 s TEMP output a Kelvin output thermom eter that operates off a single 5V supply can be built as shown in Figure 8 Since the output of the REF 43 s TEMP pin is theoretically zero at 0 K trimming adjusts both the slope and zero point In actuality the 40mV zero point found by extrapolating the TEMP voltage vs actual tempera ture to zero will create a small error 4 2Z0mA temperature transmitter is described on page 10 which uses two trims to eliminate this inaccuracy For wider temperature ranges than semiconductors can withstand thermocouples are commonly used Depending upon the type used a thermocouple can measure tempera tures over 1000 C Thermocouples require a reference junc tion at a known temperature usually 090 Since it is not generally convenient to have an ice bath electronic methods of simulating this junction have been developed called cold junction compensation In Figure 9 diode D1 is mounted isothermally to the termination of the thermocouple and along with R1and R2 provides the cold junctio
9. ITHMIC AMPLIFIER voltage is given by Vout log Vnge Rgge log Viy R iN A logarithmic amplifier accurate over more than 4 decades is thus the zero point may be adjusted by and the input shown in Figure 12 This circuit requires less than 2mA of scaling by Rin current when the input is at 1V OV output The output REV D 11 REF43 OUTLINE DIMENSIONS 8 Lead Ceramic Dual In Line Package CERDIP 8 Lead Standard Small Outline Package SOIC Q 8 R 8 Z Suffix S Suffix Dimensions shown in inches and millimeters 0 005 0 13 0 055 1 40 MIN MA 0 310 7 87 PIN 1 0 220 5 59 M 5 59 0 100 2 54 BSC 0 405 10 29 MAX 0 320 8 13 0 060 1 52 i 0 290 7 37 a 0 200 5 08 0 015 38 0 200 5 08 CIE 0 125 3 18 0 023 0 58 R Ait 0 015 0 38 0 070 1 78 0 014 0 36 0 030 0 76 PLANE 15 0 008 0 20 CONTROLLING DIMENSIONS ARE IN INCHES MILLIMETER DIMENSIONS IN PARENTHESES ARE ROUNDED OFF INCH EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN Dimensions shown in millimeters and inches 5 00 0 1968 0 1 so M 6 20 0 2440 3 80 0 1497 5 80 0 2284 1 dee 1 27 0 0500 0 50 0 0196 2 BSC 1 75 0 0688 lt 0 25 0 0099 0 25 0 0098 1 35 0 0532 0 10 0 0040 Y 0 51 0 0201 118 COPLANARITY at pe or 00201 0 25 0 0098 0 1 27 0 0500 0 10 E 0 17 0 0067 0 40 0 0157 COMPLIANT T
10. MIN TYP MAX UNITS Output Voltage 9 No Load 002 0 06 004 0 1 Tolerance Output Voltage Vo No Load 2 4985 2 5000 p 5015 2 4975 2 5000 2 5025 V Output Voltage 1OHz to 1kHz nnb T 10 7 10 u V Noise nes Note 1 4 5 Line Regulation 0 8 d 0 8 2 N 3 to 40V pm Load Regulation 14 20 14 20 gua to 10mA Quiescent No Load 340 450 340 450 A Supply Current T d Load Current 2 10 20 10 2 Sourcing IL Note 2 0 mA Load Current Note 3 1 2 1 2 Sinking 5 nd j Short Circuit Output Shorted 50 60 A Output Current to Ground Temperature Output Va our Adjust _ 95 95 mv Range Long Term AV Output Drift AVE 1 000 Hours 40 40 NOTES 1 Guaranteed but not tested 2 Guaranteed by load regulation test 3 Output remains within 2 5V 2 5mvV CAUTION ESD electrostatic discharge sensitive device Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection Although the REF43 features proprietary ESD protection circuitry permanent damage may occur on devices subjected to high energy electrostatic discharges Therefore proper ESD precautions are recommended to avoid performance degradation or loss of functionality T We dee WARNING pel ESD SENSITIVE DEVICE REV D ELECTRI
11. O JEDEC STANDARDS MS 012AA CONTROLLING DIMENSIONS ARE IN MILLIMETERS INCH DIMENSIONS IN PARENTHESES ARE ROUNDED OFF MILLIMETER EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN 8 Lead Plastic Dual In Line Package PDIP N 8 P Suffix Dimensions shown in inches and millimeters 0 375 9 53 0 365 9 27 0 355 9 02 t 0 295 7 49 0 285 7 24 0 275 6 98 K 0 325 8 26 0 310 7 87 0 300 7 62 0 150 3 81 0 135 3 43 dao 0 015 0 120 3 05 4 57 0 38 T n j MIN 0 015 0 38 0 150 3 81 SEATING 0 010 0 25 0 130 3 30 PLANE 0 008 0 20 0 110 2 79 0 060 1 52 0 022 0 56 0 050 1 27 0 018 0 46 0 045 1 14 0 014 0 36 COMPLIANT TO JEDEC STANDARDS MO 095AA CONTROLLING DIMENSIONS ARE IN INCHES MILLIMETER DIMENSIONS IN PARENTHESES ARE ROUNDED OFF INCH EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN Revision History Location 8 04 Data Sheet Changed from REV to REV D Edits to FEATURES Changes to PIN CONFIGURATION Changes to ORDERING GUIDE Changes to ABSOLUTE MAXIMUM RATINGS Changes to PACKAGE TYPE Changes to ELECTRICAL CHARACTERISTICS Delected PACKAGE TYPE C00374 0 8 04 D
12. TEMPERATURE 20 Vip Vig LSV TD 400 laur 7 mA TO 16mA laur mA 40 gt 5 B amp 5 3 12 5 5 B z 40 i 3 al c 85 5 95 65 85 100 125 55 358 18 5 26 745 65 85 5 125 TEMPERATURE PC TEMPERATURE C TEMPERATURE 4 REV D Typical Performance Characteristics REF43 SUPPLY CURRENT TEMPERATURE PIN VOLTAGE SUPPLY CURRENT vs TEMPERATURE vs TEMPERATURE ve SUPPLY VOLTAGE SUPPLY CURRENT uA TEMPERATURE VOLTAGE VOLTS SUPPLY CURRENT pA 55 35 15 5 25 4 65 85 5 135 h amp 35 1 8 35 45 65 85 4105 125 TEMPERATURE 71 TEMPERATURE C SUPPLY VOLTAGE VOLTS OUTPUT VOLTAGE CHANGE RIPPLE REJECTION OUTPUT IMPEDANCE vs SUPPLY VOLTAGE vs FREQUENCY VREGUENCY Vi 35V AM 7 lagur Om amp Ta 7 25 L HO INPUT DECOUPLING x CUT LIME TIS g 30d 30k 100k iM 19 1 SUPPLY VOLTAGE VOLTS FREGUENCY FREQUENCY Hr NL 4 th meae RIPPLE REJECTION dB OUTPUT VOLTAGE CHANGE uY OUTPUT IMPEDANCE N WIDEBAND OUTPUT NOISE BANDWIDTH 0 1Hz TO OUTPUT VOLTAGE CHANGE BURN IN DRIFT FREQUENCY INDICATED ve LOAD CURRENT AT Ta 150 C 1000 MEAN DRIFT 22 n 957 OUTPUT NOISE uv OUTPUT VOLTAGE CHANGE OUTPUT VOLTAGE DRIFT mV
13. e boost transistor In Figure 5b the limit occurs when the voltage dropped across R2 exceeds one Vgg 0 6V The current limit is sensitive to the variations of the diodes forward drop and the PNP s Vege with temperature and will decrease with increasing temperature FIGURE 5 Output Current Boost a No Current Limit b 100mA Current Limit 202905 Vin 43 Vout 0 T 100mA GAC REF43 LOW POWER CMOS DAC REFERENCE The REF 43 makes an excellent reference for use with CMOS and bipolar DACs Figure 6 shows the REF 43 connected to the DAC 8012 a 12 bit parallel loading CMOS DAC with memory With an OP 43 output amplifier for fast settling the circuit requires less than 3mA when driven from TTL gates and less than 2mA when driven from CMOS gates In situa tions not requiring the higher speed of the OP 43 enhanced linearity and some savings in power dissipation can be real ized using an OP 97 for the output amplifier FIGURE 6 CMOS DAC Reference PRECISION CURRENT SOURCE Current sources are often required in analog processing and computational circuits The circuit of Figure 7 shows a high output impedance current source capable of single supply operation Performance is optimal at current levels below 1mA since output voltage changes directly affect the power dissipated within the REF 43 DIGITAL INPUT L Vo 0V TO 2 5V OP AMP IS OP43 IF HIGHER SPEED AND FASTER SETTING IS REQUIRED OP97 IF LOWER SP
14. gure 2A while the transient response of the REF 43 to a sudden 2mA load is shown in Figures 2B and 2C As can be seen from Figure 2B if the reference Is given 1 us to settle after applica tion or removal of the load no output decoupling is necessary Load regulation is a measure of the DC output impedance of the reference For the REF 43 this value is specified at 20 Max which is equivalent to only 50 milliohms of output impedance It is obvious that to truly realize this per formance level wiring resistances from the reference to the rest of the system must be kept as low as is practical The REF 43 is capable of delivering at least 10mA to a load To maintain its precision operation loads should be kept within the 10mA specification High speed testing requires that load regulation is measured on a pulse basis therefore FIGURE 2A Hecommended Decoupling for High Frequency Pulse Response 0 01nF TO TANTALUM FIGURE 2C Pulse Response with Output Decoupling when calculating the output voltage tolerance within a sys tem the effects of current delivered to the load must be accounted for both as load regulation and as a temperature increase due to power dissipated within the IC In AC sys tems the RMS power dissipation should be used Thermal effects can be significant since a REF 43 delivering 10mA with an input voltage of 40V must dissipate almost 400mW of power In the 99 package 400mW of
15. is affected by the internal trimming done for output voltage tolerance and will vary between units If theTemperature Pin 3 is connected to external circuitry it should be buffered by an op amp Current into or out of Pin 3 will change the temperature coefficient and curvature of the output voltage while capacitance at the pin can create instabilities within the reference amplifier GENERATING A 2 5V REFERENCE Often there is a requirement for a negative reference voltage The simplest method of generating a 2 5 reference with the REF 43 is to connect an amp in a gain of 1 to the output as shown in Figure 3 This provides both positive and nega tive 2 5V references Figure 4 shows another method of obtaining a negative reference in which the current output FIGURE 3 2 5V Reference VIN REF 43 GAD 190 0 100611 REV D element is a PNP transistor with the REF 43 in a servo loop to ensure that the output remains 2 5V below ground BOOST TRANSISTOR PROVIDES HIGH OUTPUT CURRENT When applications require more than 10mA current delivery an external boost transistor may be added to the REF 43 to pass the required current without dissipating excessive power within the IC The maximum current output to the system is bounded only by the capabilities of the boost tran sistor This technique is shown in Figure 5 with and without current limiting Current limiting may be used to prevent damage to th
16. l 10 200 300 ano FREQUENCY Hz LOAD CURRENT mA H URS OF ORR RATION AT 150C 10 100 1k TER 1M REV D 5 REF43 APPLICATIONS INFORMATION The REF 43 provides a stable 2 5V output voltage with minimal dependence on load current line voltage or temper ature This voltage is typically used to set an absolute refer ence point in data conversion circuits or in analog circuits such as log amps 4 20m transmitters and power supplies 43 is of particular value in systems requiring high precision reference using a single 5V supply rail or where power dissipation must be minimized Because an onboard operational amplifier is used to amplify the basic band gap cell voltage to 2 5V supply decoupling is critical to the transient performance of a voltage reference The supply line should be bypassed with a 10uF tantalum capacitor in parallel with a 0 01 uF to 0 1u4F ceramic capacitor for best results For less critical conditions a single 0 1uF capacitor is adequate FIGURE 1 Basic Connections Your 2 5 Output decoupling is not generally required or recom mended except to achieve the lowest possible high frequency output impedance when loads are being switched in and out quickly was the case with supply decoupling best results will be achieved with 10uF tantalum capacitor in parallel with a 0 01uF to O 1uF ceramic capacitor Recom mended high frequency decoupling is shown in Fi
17. n campensa tion required for accurate measurement Using an OP 90 as the amplifier the circuit will operate off a single 5V supply and is capable of measuring temperaturas from O C to 400 C If negative temperatures must be measured dual supplies must be used to allow the op amp to swing negative In cases where the electronics are subject to temperature fluctuations an OP 77 is recommended for its extremely low TCVos REV D Calibration of the thermocouple amplifier is done after a 15 minute warm up time using R5 A copper wire shortis placed across the thermocouple terminating junctions simulating condition R5 is then adjusted for a 0 00 output The short isthen removed and the amplifier is ready for use Mote that special care must be used in calibration when this circuit is operated single supply as the output of the OP 90 will swing to within 5DOuV of ground but not below ground Thus H5 must be trimmed t the point where the output just barely reaches its swing limit By changing the appropriate resistor values the amplifier may ba used with type S J or K thermocouples In all cases the output has been scaled with R8 to provide an output of 1l 0mVv C SEEBECK TYPE COEFFICIENT R1 R2 R7 R8 K 39 24 V C 11001 578 102 269k J 50 2uV C 1000 402 80 0 5 10 10041 20 5 LOTMA TWO WIRE 4 20mA TRANSMITTERS 4 20mA current loops are used in noisy enviro
18. nments for many types of remote data acquisition With a two wire loop the sensing circuitry can be powered with the same lines used for signal transmission REF43 FIGURE 10 Two Wire 4 20mA Transmitter 2 5V REFERENCE 2 The current transmitter of Figure 10 provides an output of 4mA to 20mA that is linearly proportional to the input voltage Linearity of the transmitter exceeds 0 00496 and line rejection is below measurement limits Biasing for the current transmitter is provided by the REF 43FZ The OP 90EZ regulates the output current to satisfy the current summation at the noninverting node 25VR5 ONT R6 R2 R1 For the values shown in Figure 10 16 v 4mA OUT 1000 IM giving a full scale output of 20mA with a 100mV input Adjustment of R2 will provide an offset trim and adjustment of R1 will provide a gain trim These trims do not interact since the noninverting input of the OP 90 is atvirtual ground The Schottky diode D1 prevents input voltage spikes from pulling the noninverting input more than 300mV below the inverting input Without the diode such spikes could cause phase reversal of the OP 90 and possible latch up of the transmitter Compliance of this circuit is from 4 5V to 40V The voltage reference output can provide up to 2 for trans ducer excitation The OP 90 is also available in dual and quad versions Using an OP 490 three ofthe amplifiers can be usedtoim
19. plement a full instrumentation amplifier for signal conditioning before delivery to the 4 20mA transmitter All four OP 90s require less than 80uA supply current and thus have virtually no impact on the current budget of the 4 20mA loop simple temperature to 4 20mA transmitter is shownin Figure 11 After calibration the transmitter is accurate to within 1 C over the 50 C to 150 C temperature range The transmitter operates from 6V to 40V with supply rejection better than 10 4 5V TO 400 3ppm V An OP 90 is used to buffer the TEMP pin while the second OP 90 regulates the output current to satisfy the current summation at its noninverting input Ho Ret Ret H7 ppc Ead obe H5 R4p H2 Rig The change in output current with temperature is the deriva tive of the transfer function AVTEMP AlouT AT 86 Ra Rip From the formulas it can be seen that if the gain trim is adjusted before the final offset trim the two trims are not interactive which greatly simplifies the calibration procedure To calibrate the transmitter begin by placing the REF 43 in ice water 0 C bath If necessary adjust the offset trim R5 so that the output current is above 4mA Record the output current Next place the REF 02 in a boil ing water 100 C bath Adjust the gain trim R6 so that the change in the output current reflects the desired mA C ratio described as follows Alrs
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ANALOG DEVICES REF43: 2.5 V Low Power Precision Voltage Reference Data Sheet (Rev D 2004 08 01 ) han