XTR105 XTR 105 XTR 105 SBOS061B – FEBRUARY 1997 – REVISED AUGUST 2004 4-20mA CURRENT TRANSMITTER with Sensor Excitation and Linearization FEATURES APPLICATIONS ● ● ● ● ● ● ● ● ● ● ● ● ● ● DESCRIPTION The XTR105 is a monolithic 4-20mA, 2-wire current transmitter with two precision current sources. It provides complete current excitation for platinum RTD temperature sensors and bridges, instrumentation amplifiers, and current output circuitry on a single integrated circuit. INDUSTRIAL PROCESS CONTROL FACTORY AUTOMATION SCADA REMOTE DATA ACQUISITION REMOTE TEMPERATURE AND PRESSURE TRANSDUCERS Pt100 NONLINEARITY CORRECTION USING XTR105 5 4 Nonlinearity (%) LOW UNADJUSTED ERROR TWO PRECISION CURRENT SOURCES: 800µA each LINEARIZATION 2- OR 3-WIRE RTD OPERATION LOW OFFSET DRIFT: 0.4µV/°C LOW OUTPUT CURRENT NOISE: 30nAPP HIGH PSR: 110dB minimum HIGH CMR: 86dB minimum WIDE SUPPLY RANGE: 7.5V to 36V DIP-14 AND SO-14 PACKAGES Uncorrected RTD Nonlinearity 2 1 Corrected Nonlinearity 0 −1 −200°C Versatile linearization circuitry provides a 2nd-order correction to the RTD, typically achieving a 40:1 improvement in linearity. Instrumentation amplifier gain can be configured for a wide range of temperature or pressure measurements. Total unadjusted error of the complete current transmitter is low enough to permit use without adjustment in many applications. This includes zero output current drift, span drift, and nonlinearity. The XTR105 operates on loop power-supply voltages down to 7.5V. 3 +850°C Process Temperature (°C) IR = 0.8mA IR = 0.8mA VLIN VREG 7.5V to 36V + VPS 4-20 mA RTD The XTR105 is available in DIP-14 and SO-14 surfacemount packages and is specified for the –40°C to +85°C industrial temperature range. XTR105 RG VO RL – Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. All trademarks are the property of their respective owners. Copyright © 1997-2004, Texas Instruments Incorporated PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. www.ti.com ABSOLUTE MAXIMUM RATINGS(1) ELECTROSTATIC DISCHARGE SENSITIVITY Power Supply, V+ (referenced to the IO pin) ...................................... 40V Input Voltage, VIN+, VIN– (referenced to the IO pin) .................... 0V to V+ Storage Temperature Range ......................................... –55°C to +125°C Lead Temperature (soldering, 10s) ............................................... +300°C Output Current Limit ................................................................ Continuous Junction Temperature .................................................................... +165°C This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. NOTE: (1) Stresses above those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. Exposure to absolute maximum conditions for extended periods may affect device reliability. ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. PACKAGE/ORDERING INFORMATION(1) PACKAGE-LEAD PACKAGE DESIGNATOR SPECIFIED TEMPERATURE RANGE DIP-14 N –40°C to +85°C " " " SO-14 Surface-Mount D –40°C to +85°C " " " SO-14 Surface-Mount D –40°C to +85°C " " " PRODUCT XTR105 " XTR105 " XTR105 " PACKAGE MARKING ORDERING NUMBER TRANSPORT MEDIA, QUANTITY XTR105PA XTR105P XTR105UA XTR105UA XTR105U XTR105U XTR105PA XTR105P XTR105UA XTR105UA/2K5 XTR105U XTR105U/2K5 Rails, 25 Rails, 25 Rails, 58 Tape and Reel, 2500 Rails, 58 Tape and Reel, 2500 NOTE: (1) For the most current package and ordering information, see the Package Option Addendum located at the end of this data sheet. FUNCTIONAL BLOCK DIAGRAM PIN CONFIGURATION Top View DIP and SO VLIN IR1 12 IR2 1 14 VREG V+ 800µA 800µA 11 + VIN 13 5.1V 4 B RLIN 1kΩ Q1 9 100µA RG 3 – VIN 1 14 IR2 – VIN 2 13 VIN RG 3 12 VLIN RG 4 11 VREG NC 5 10 V+ IRET 6 9 B (Base) IO 7 8 E (Emitter) IR1 10 E I = 100µA + 2 VIN 8 RG 975Ω + 25Ω NC = No Internal Connection 7 IO = 4mA + VIN • ( R40 ) G 6 IRET 2 XTR105 www.ti.com SBOS061B ELECTRICAL CHARACTERISTICS At TA = +25°C, V+ = 24V, and TIP29C external transistor, unless otherwise noted. XTR105P, U PARAMETER CONDITIONS OUTPUT Output Current Equation Output Current, Specified Range Over-Scale Limit Under-Scale Limit OUTPUT(1) ZERO Initial Error vs Temperature vs Supply Voltage, V+ vs Common-Mode Voltage vs VREG Output Current Noise, 0.1Hz to 10Hz SPAN Span Equation (transconductance) Initial Error (3) vs Temperature(3) Nonlinearity, Ideal Input (4) INPUT(5) Offset Voltage vs Temperature vs Supply Voltage, V+ vs Common-Mode Voltage, RTI (CMRR) Common-Mode Input Range(2) Input Bias Current vs Temperature Input Offset Current vs Temperature Impedance, Differential Common-Mode Noise, 0.1Hz to 10Hz CURRENT SOURCES Current Accuracy vs Temperature vs Power Supply, V+ Matching vs Temperature vs Power Supply, V+ Compliance Voltage, Positive Negative(2) Output Impedance Noise, 0.1Hz to 10Hz IREG = 0V MIN TYP XTR105PA, UA MAX MIN TYP IO = VIN • (40/RG) + 4mA, VIN in Volts, RG in Ω 4 20 ✻ 24 27 30 ✻ ✻ 1.8 2.2 2.6 ✻ ✻ VIN = 0V, RG = ∞ 4 ±5 ±0.07 0.04 0.02 0.3 0.03 V+ = 7.5V to 36V VCM = 1.25V to 3.5V(2) Full-Scale (VIN) = 50mV Full-Scale (VIN) = 50mV VCM = 2V V+ = 7.5V to 36V VCM = 1.25V to 3.5V(2) ✻ ✻ ✻ ✻ ✻ ✻ ✻ ±25 ±0.5 0.2 MAX UNITS ✻ ✻ ✻ A mA mA mA ±50 ±0.9 ✻ S = 40/RG ±0.05 ±3 0.003 ±0.2 ±25 0.01 ✻ ✻ ✻ ✻ ±0.4 ✻ ✻ A/V % ppm/°C % ±50 ±0.4 ±0.3 ±10 ±100 ±1.5 ±3 ±50 ✻ ✻ ✻ ✻ ±250 ±3 ✻ ±100 µV µV/°C µV/V µV/V ✻ 50 V nA pA/°C nA pA/°C GΩ || pF GΩ || pF µVPP 1.25 5 20 ±0.2 5 0.1 || 1 5 || 10 0.6 3.5 25 ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ±3 ±10 VO = 2V(6) V+ = 7.5V to 36V V+ = 7.5V to 36V (V+) – 3 0 800 ±0.05 ±15 ±10 ±0.02 ±3 1 (V+) – 2.5 –0.2 150 0.003 VREG(2) Accuracy vs Temperature vs Supply Voltage, V+ Output Current Output Impedance 5.1 ±0.02 ±0.2 1 ±1 75 LINEARIZATION RLIN (internal) Accuracy vs Temperature 1 ±0.2 ±25 POWER SUPPLY Specified Voltage Range TEMPERATURE RANGE Specification, TMIN to TMAX Operating Storage Thermal Resistance, θJA DIP-14 SO-14 Surface-Mount mA µA µA/°C µA/V µA/V µA/mA µAPP ±0.2 ±35 ±25 ±0.1 ±15 10 ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ±0.1 ✻ ✻ ✻ ±0.5 ±100 ±0.4 ±75 ✻ ±0.2 ±30 ✻ ✻ V V mV/°C mV/V mA Ω ±1 ✻ kΩ % ppm/°C ✻ +24 µA % ppm/°C ppm/V % ppm/°C ppm/V V V MΩ µAPP +7.5 +36 ✻ ✻ V V –40 –55 –55 +85 +125 +125 ✻ ✻ ✻ ✻ ✻ ✻ °C °C °C 80 100 ✻ ✻ °C/W °C/W ✻ Specification same as XTR105P and XTR105U. NOTES: (1) (2) (3) (4) (5) (6) Describes accuracy of the 4mA low-scale offset current. Does not include input amplifier effects. Can be trimmed to zero. Voltage measured with respect to IRET pin. Does not include initial error or TCR of gain-setting resistor, RG. Increasing the full-scale input range improves nonlinearity. Does not include Zero Output initial error. Current source output voltage with respect to IRET pin. XTR105 SBOS061B www.ti.com 3 TYPICAL CHARACTERISTICS At TA = +25°C and V+ = 24V, unless otherwise noted. TRANSCONDUCTANCE vs FREQUENCY STEP RESPONSE RG = 125Ω RG = 500Ω RG = 2kΩ 40 20mA 30 4mA/div Transconductance (20 Log mA/V) 50 20 RG = 125Ω RG = 2kΩ 4mA 10 0 100 1k 10k 100k 25µs/div 1M Frequency (Hz) COMMON-MODE REJECTION vs FREQUENCY POWER-SUPPLY REJECTION vs FREQUENCY 140 Full-Scale Input = 50mV 100 Power Supply Rejection (dB) Common-Mode Rejection (dB) 110 90 80 RG = 125Ω 70 60 RG = 2kΩ 50 40 30 20 120 RG = 125Ω 100 80 RG = 2kΩ 60 40 20 0 10 100 1k 10k 100k 1M 10 100 Frequency (Hz) 1k 10k 100k 1M Frequency (Hz) UNDER-SCALE CURRENT vs TEMPERATURE OVER-SCALE CURRENT vs TEMPERATURE 2.40 29 Under-Scale Current (mA) Over-Scale Current (mA) With External Transistor 28 27 V+ = 36V 26 V+ = 7.5V 25 V+ = 24V 24 2.30 2.25 2.20 V+ = 7.5V to 36V 23 2.15 –75 –50 –25 0 25 50 75 100 –75 125 –50 –25 0 25 50 75 100 125 Temperature (°C) Temperature (°C) 4 2.35 XTR105 www.ti.com SBOS061B TYPICAL CHARACTERISTICS (Cont.) At TA = +25°C and V+ = 24V, unless otherwise noted. ZERO OUTPUT AND REFERENCE CURRENT NOISE vs FREQUENCY INPUT VOLTAGE AND CURRENT NOISE DENSITY vs FREQUENCY 10k 10k 1k Current Noise 100 100 Voltage Noise 10 1 10 100 1k Zero Output Current Noise (pA/√Hz) 1k Input Current Noise (fA/√Hz) Input Voltage Noise (nV/√Hz) 10k 1k 100 Reference Current 10 10 100k 10k 1 1k 10k INPUT BIAS AND OFFSET CURRENT vs TEMPERATURE ZERO OUTPUT CURRENT ERROR vs TEMPERATURE 100k 4 20 15 +IB 10 –IB 5 IOS Zero Output Current Error (µA) Input Bias and Offset Current (nA) 100 Frequency (Hz) 25 2 0 –2 –4 –6 –8 –10 –12 0 –75 –50 –25 0 25 50 75 100 –75 125 –50 –25 0 25 50 75 Temperature (°C) Temperature (°C) INPUT OFFSET VOLTAGE DRIFT PRODUCTION DISTRIBUTION ZERO OUTPUT DRIFT PRODUCTION DISTRIBUTION 50 100 125 40 Typical Production Distribution of Packaged Units. 45 35 Percent of Units (%) 40 Percent of Units (%) 10 Frequency (Hz) 35 30 25 20 15 10 0.02% 0.1% 5 Typical Production Distribution of Packaged Units. 30 25 20 15 10 5 0 0.025 0.050 0.075 0.100 0.125 0.150 0.175 0.200 0.225 0.250 0.275 0.300 0.325 0.350 0.375 0.400 0.425 0.450 0.475 0.500 3.0 2.8 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 Input Offset Voltage Drift (µV/°C) Zero Output Drift (µA/°C) XTR105 SBOS061B www.ti.com 5 TYPICAL CHARACTERISTICS (Cont.) At TA = +25°C and V+ = 24V, unless otherwise noted. CURRENT SOURCE DRIFT PRODUCTION DISTRIBUTION CURRENT SOURCE MATCHING DRIFT PRODUCTION DISTRIBUTION 40 80 30 Current Source Drift (ppm/°C) Current Source Matching Drift (ppm/°C) VREG OUTPUT VOLTAGE vs VREG OUTPUT CURRENT REFERENCE CURRENT ERROR vs TEMPERATURE 30 0.02% 28 0.07% 26 12 8 10 6 4 2 75 70 60 55 50 45 40 35 30 25 20 15 0 5 0 10 10 24 20 0.01% 5 22 10 40 20 15 50 18 20 60 14 25 0.04% Typical Production Distribution of Packaged Units. 70 Percent of Units (%) 30 65 Percent of Units (%) 35 16 Typical Production Distribution of Packaged Units. IR1 AND IR2 Included. +0.05 5.35 125°C 5.25 Reference Current Error (%) VREG Output Voltage (V) 5.30 25°C 5.20 5.15 –55°C NOTE: Above 1mA, Zero Output Degrades 5.10 5.05 5.00 –1.0 –0.05 –0.10 –0.15 –0.20 –0.5 0 0.5 1.0 1.5 –75 2.0 –50 –25 0 25 50 75 100 125 Temperature (°C) VREG Output Current (mA) 6 0 XTR105 www.ti.com SBOS061B APPLICATION INFORMATION The transfer function through the complete instrumentation amplifier and voltage-to-current converter is: Figure 1 shows the basic connection diagram for the XTR105. The loop power supply, VPS, provides power for all circuitry. Output loop current is measured as a voltage across the series load resistor, RL. IO = 4mA + VIN • (40/RG) (VIN in volts, RG in ohms) where VIN is the differential input voltage. As evident from the transfer function, if no RG is used the gain is zero and the output is simply the XTR105’s zero current. The value of RG varies slightly for 2-wire RTD and 3wire RTD connections with linearization. RG can be calculated from the equations given in Figure 1 (2-wire RTD connection) and Table I (3-wire RTD connection). Two matched 0.8mA current sources drive the RTD and zero-setting resistor, RZ. The instrumentation amplifier input of the XTR105 measures the voltage difference between the RTD and RZ. The value of RZ is chosen to be equal to the resistance of the RTD at the low-scale (minimum) measurement temperature. RZ can be adjusted to achieve 4mA output at the minimum measurement temperature to correct for input offset voltage and reference current mismatch of the XTR105. The IRET pin is the return path for all current from the current sources and VREG. The IRET pin allows any current used in external circuitry to be sensed by the XTR105 and to be included in the output current without causing an error. RCM provides an additional voltage drop to bias the inputs of the XTR105 within their common-mode input range. RCM should be bypassed with a 0.01µF capacitor to minimize common-mode noise. Resistor RG sets the gain of the instrumentation amplifier according to the desired temperature range. RLIN1 provides 2nd-order linearization correction to the RTD, typically achieving a 40:1 improvement in linearity. An additional resistor is required for 3-wire RTD connections (see Figure 3). The VREG pin provides an on-chip voltage source of approximately 5.1V and is suitable for powering external input circuitry (refer to Figure 6). It is a moderately accurate voltage reference—it is not the same reference used to set the 800µA current references. VREG is capable of sourcing approximately 1mA of current. Exceeding 1mA may affect the 4mA zero output. IR = 0.8mA Possible choices for Q1 (see text). IR = 0.8mA 12 13 4 VLIN + VIN 1 IR1 TO-225 TO-220 TO-220 IO RG RG RLIN1(3) PACKAGE 7.5V to 36V 14 11 IR2 10 VREG V+ 4-20 mA (2) XTR105 3 TYPE 2N4922 TIP29C TIP31C RG B 9 Q1 0.01µF VO E 8 RL IO 2 – VIN + VPS – 7 IRET RTD (1) RZ 6 IO = 4mA + VIN • ( 40 ) RG NOTES: (1) RZ = RTD resistance at minimum measured temperature. RCM = 1kΩ (2) RG = (3) RLIN1 = 0.01µF 2R1(R2 +RZ) – 4(R2RZ) R2 – R1 RLIN(R2 – R1) 2(2R1 – R2 – RZ) where R1 = RTD Resistance at (TMIN + TMAX)/2 R2 = RTD Resistance at TMAX RLIN = 1kΩ (Internal) FIGURE 1. Basic 2-Wire RTD Temperature Measurement Circuit with Linearization. XTR105 SBOS061B www.ti.com 7 MEASUREMENT TEMPERATURE SPAN ∆T (°C) TMIN 100°C 200°C 300°C 400°C 500°C 600°C 700°C 800°C 900°C 1000°C –200°C 18.7/86.6 15000 16500 18.7/169 9760 11500 18.7/255 8060 10000 18.7/340 6650 8870 18.7/422 5620 7870 18.7/511 4750 7150 18.7/590 4020 6420 18.7/665 3480 5900 18.7/750 3090 5360 18.7/845 2740 4990 –100°C 60.4/80.6 27400 29400 60.4/162 15400 17800 60.4/243 10500 13000 60.4/324 7870 10200 60.4/402 6040 8660 60.4/487 4990 7500 60.4/562 4220 6490 60.4/649 3570 5900 60.4/732 3090 5360 0°C 100/78.7 33200 35700 100/158 16200 18700 100/237 10500 13000 100/316 7680 10000 100/392 6040 8250 100/475 4870 7150 100/549 4020 6340 100/634 3480 5620 100°C 137/75 31600 34000 137/150 15400 17800 137/226 10200 12400 137/301 7500 9760 137/383 5760 8060 137/453 4750 6810 137/536 3920 6040 200°C 174/73.2 30900 33200 174/147 15000 17400 174/221 9760 12100 174/294 7150 9310 174/365 5620 7680 174/442 4530 6490 300°C 210/71.5 30100 32400 210/143 14700 16500 210/215 9530 11500 210/287 6980 8870 210/357 5360 7320 400°C 249/68.1 28700 30900 249/137 14000 16200 249/205 9090 11000 249/274 6650 8450 500°C 280/66.5 28000 30100 280/133 13700 15400 280/200 8870 10500 316/64.9 26700 28700 313/130 13000 14700 600°C 700°C 800°C RZ /RG RLIN1 RLIN2 NOTE: The values listed in this table are 1% resistors (in Ω). Exact values may be calculated from the following equations: RZ = RTD resistance at minimum measured temperature. RG = 348/61.9 26100 27400 374/60.4 24900 26700 2(R2 – RZ )(R1 – RZ ) (R2 – R1) RLIN1 = RLIN (R2 – R1) 2(2R1 – R2 – RZ ) RLIN2 = (RLIN + RG )(R2 – R1) 2(2R1 – R2 – RZ ) where: R1 = RTD resistance at (TMIN + TMAX)/2 R2 = RTD resistance at TMAX RLIN = 1kΩ (Internal) EXAMPLE: The measurement range is –100°C to +200°C for a 3-wire Pt100 RTD connection. Determine the values for RS, RG, RLIN1, and RLIN2. Look up the values from the chart or calculate the values according to the equations provided. METHOD 1: TABLE LOOK UP For TMIN = –100°C and ∆T = –300°C, the 1% values are: RZ = 60.4Ω RLIN1 = 10.5kΩ RG = 243Ω RLIN2 = 13kΩ METHOD 2: CALCULATION Calculation of Pt100 Resistance Values Step 1: Determine RZ, R1, and R2. (according to DIN IEC 751) RZ is the RTD resistance at the minimum measured temperature,TMIN = –100°C. Using Equation 1 at right gives RZ = 60.25Ω (1% value is 60.4Ω). R2 is the RTD resistance at the maximum measured temperature, TMAX = 200°C. Using Equation 2 at right gives R2 = 175.84Ω. R1 is the RTD resistance at the midpoint measured temperature, TMID = (TMIN + TMAX) /2 = 50°C. R1 is NOT the average of RZ and R2. Using Equation 2 at right gives R1 = 119.40Ω. (Equation 1) Temperature range from –200°C to 0°C: R(T) = 100 [1 + 3.90802 • 10–3 • T – 0.5802 • 10–6 • T2 – 4.27350 • 10–12 (T – 100) T3] (Equation 2) Temperature range from 0°C to +850°C: R(T) = 100 (1 + 3.90802 • 10–3 • T – 0.5802 • 10–6 • T2) where: R(T) is the resistance in Ω at temperature T. T is the temperature in °C. Step 2: Calculate RG, RLIN1, and RLIN2 using equations above. NOTE: Most RTD manufacturers provide reference tables for resistance values at various temperatures. RG = 242.3Ω (1% value is 243Ω) RLIN1 = 10.413kΩ (1% value is 10.5kΩ) RLIN2 = 12.936kΩ (1% value is 13kΩ) TABLE I. RZ, RG, RLIN1, and RLIN2 Standard 1% Resistor Values for 3-Wire Pt100 RTD Connection with Linearization. A negative input voltage, VIN, will cause the output current to be less than 4mA. Increasingly negative VIN will cause the output current to limit at approximately 2.2mA. Refer to the typical characteristic Under-Scale Current vs Temperature. 8 Increasingly positive input voltage (greater than the full-scale input) will produce increasing output current according to the transfer function, up to the output current limit of approximately 27mA. Refer to the typical characteristic Over-Scale Current vs Temperature. XTR105 www.ti.com SBOS061B EXTERNAL TRANSISTOR Transistor Q1 conducts the majority of the signal-dependent 4-20mA loop current. Using an external transistor isolates the majority of the power dissipation from the precision input and reference circuitry of the XTR105, maintaining excellent accuracy. Since the external transistor is inside a feedback loop, its characteristics are not critical. Requirements are: VCEO = 45V min, β = 40 min, and PD = 800mW. Power dissipation requirements may be lower if the loop power-supply voltage is less than 36V. Some possible choices for Q1 are listed in Figure 1. The XTR105 can be operated without this external transistor, however, accuracy will be somewhat degraded due to the internal power dissipation. Operation without Q1 is not recommended for extended temperature ranges. A resistor (R = 3.3kΩ) connected between the IRET pin and the E (emitter) pin may be needed for operation below 0°C without Q1 to ensure the full 20mA full-scale output, especially with V+ near 7.5V. 10 8 XTR105 The low operating voltage (7.5V) of the XTR105 allows operation directly from personal computer power supplies (12V ±5%). When used with the RCV420 current loop receiver (see Figure 7), the load resistor voltage drop is limited to 3V. ADJUSTING INITIAL ERRORS Many applications require adjustment of initial errors. Input offset and reference current mismatch errors can be corrected by adjustment of the zero resistor, RZ. Adjusting the gain-setting resistor, RG, corrects any errors associated with gain. 2- AND 3-WIRE RTD CONNECTIONS In Figure 1, the RTD can be located remotely simply by extending the two connections to the RTD. With this remote 2-wire connection to the RTD, line resistance will introduce error. This error can be partially corrected by adjusting the values of RZ, RG, and RLIN1. A better method for remotely located RTDs is the 3-wire RTD connection (see Figure 3). This circuit offers improved accuracy. RZ’s current is routed through a third wire to the RTD. Assuming line resistance is equal in RTD lines 1 and 2, this produces a small common-mode voltage that is rejected by the XTR105. A second resistor, RLIN2, is required for linearization. V+ E It is recommended to design for V+ equal or greater than 7.5V with loop currents up to 30mA to allow for out-of-range input conditions. 0.01µF Note that although the 2-wire and 3-wire RTD connection circuits are very similar, the gain-setting resistor, RG, has slightly different equations: IO 7 IRET 2-wire: 6 RQ = 3.3kΩ For operation without an external transistor, connect a 3.3kΩ resistor between pin 6 and pin 8. See text for discussion of performance. 3-wire: RG = 2R1(R2 + RZ ) – 4(R2RZ ) R2 – R1 RG = 2(R2 – RZ )(R1 – RZ ) R2 – R1 where: RZ = RTD resistance at TMIN R1 = RTD resistance at (TMIN + TMAX)/2 FIGURE 2. Operation Without an External Transistor. R2 = RTD resistance at TMAX LOOP POWER SUPPLY The voltage applied to the XTR105, V+, is measured with respect to the IO connection, pin 7. V+ can range from 7.5V to 36V. The loop-supply voltage, VPS, will differ from the voltage applied to the XTR105 according to the voltage drop on the current sensing resistor, RL (plus any other voltage drop in the line). If a low loop-supply voltage is used, RL (including the loop wiring resistance) must be made a relatively low value to assure that V+ remains 7.5V or greater for the maximum loop current of 20mA: (V + ) – 7.5V RL max = – RWIRING 20mA To maintain good accuracy, at least 1% (or better) resistors should be used for RG. Table I provides standard 1% RG resistor values for a 3-wire Pt100 RTD connection with linearization. LINEARIZATION RTD temperature sensors are inherently (but predictably) nonlinear. With the addition of one or two external resistors, RLIN1 and RLIN2, it is possible to compensate for most of this nonlinearity resulting in 40:1 improvement in linearity over the uncompensated output. See Figure 1 for a typical 2-wire RTD application with linearization. Resistor RLIN1 provides positive feedback and controls linearity correction. RLIN1 is chosen according to the desired temperature range. An equation is given in Figure 1. XTR105 SBOS061B www.ti.com 9 In 3-wire RTD connections, an additional resistor, RLIN2, is required. As with the 2-wire RTD application, RLIN1 provides positive feedback for linearization. RLIN2 provides an offset canceling current to compensate for wiring resistance encountered in remotely located RTDs. RLIN1 and RLIN2 are chosen such that their currents are equal. This makes the voltage drop in the wiring resistance to the RTD a commonmode signal that is rejected by the XTR105. The nearest standard 1% resistor values for RLIN1 and RLIN2 should be adequate for most applications. Table I provides the 1% resistor values for a 3-wire Pt100 RTD connection. If no linearity correction is desired, the VLIN pin should be left open. With no linearization, RG = 2500 • VFS, where VFS = full-scale input range. RTDs The text and figures thus far have assumed a Pt100 RTD. With higher resistance RTDs, the temperature range and input voltage variation should be evaluated to ensure proper common-mode biasing of the inputs. As mentioned earlier, RCM can be adjusted to provide an additional voltage drop to bias the inputs of the XTR105 within their common-mode input range. RLIN1(1) ERROR ANALYSIS See Table II for how to calculate the effect various error sources have on circuit accuracy. A sample error calculation for a typical RTD measurement circuit (Pt100 RTD, 200°C measurement span) is provided. The results reveal the XTR105’s excellent accuracy, in this case 1.1% unadjusted. Adjusting resistors RG and RZ for gain and offset errors improves circuit accuracy to 0.32%. Note that these are worst-case errors; ensured maximum values were used in the calculations and all errors were assumed to be positive (additive). The XTR105 achieves performance that is difficult to obtain with discrete circuitry and requires less space. OPEN-CIRCUIT PROTECTION The optional transistor Q2 in Figure 3 provides predictable behavior with open-circuit RTD connections. It assures that if any one of the three RTD connections is broken, the XTR105’s output current will go to either its high current limit (≈ 27mA) or low current limit (≈ 2.2mA). This is easily detected as an out-of-range condition. 13 RLIN2(1) 4 12 1 VLIN IR1 + VIN IO 14 IR2 11 10 VREG V+ RG (1) RG XTR105 3 2 B 9 E RG Q1 0.01µF 8 IO – VIN 7 IRET EQUAL line resistances here creates a small common-mode voltage which is rejected by the XTR105. RZ(1) IO 6 1 2 RCM = 1000Ω (RLINE2) RTD (RLINE1) NOTES: (1) See Table I for resistor equations and 1% values. (2) Q2 optional. Provides predictable output current if any one RTD connection is broken: Q2(2) 2N2222 (RLINE3) Resistance in this line causes a small common-mode voltage which is rejected by the XTR105. 0.01µF 3 OPEN RTD TERMINAL IO 1 2 3 ≈ 2.2mA ≈27mA ≈2.2mA FIGURE 3. Remotely Located RTDs with 3-Wire Connection. 10 XTR105 www.ti.com SBOS061B SAMPLE ERROR CALCULATION RTD value at 4mA Output (RRTD MIN): RTD Measurement Range: Ambient Temperature Range (∆TA): Supply Voltage Change (∆V+): Common-Mode Voltage Change (∆CM): ERROR SOURCE INPUT Input Offset Voltage vs Common-Mode Input Bias Current Input Offset Current EXCITATION Current Reference Accuracy vs Supply Current Reference Matching vs Supply 100Ω 200°C 20°C 5V 0.1V ERROR EQUATION VOS/(VIN MAX) • 106 CMRR • ∆CM/(VIN MAX) • 106 IB/IREF • 106 IOS • RRTD MIN/(VIN MAX) • 106 IREF Accuracy (%)/100% • 106 (IREF vs V+) • ∆V+ IREF Matching (%)/100% • 800µA • RRTD MIN/(VIN MAX) • 106 (IREF Matching vs V+) • ∆V+ • RRTD MIN/(VIN MAX) ERROR (ppm of Full Scale) SAMPLE ERROR CALCULATION(1) UNADJ. ADJUST. 1645 82 31 5 1763 0 82 0 0 82 0.2%/100% • 106 25ppm/V • 5V 0.1%/100% • 800µA • 100Ω/(800µA • 0.38Ω/°C • 200°C) • 106 2000 125 1316 0 125 0 10ppm/V • 5V • 800µA • 100Ω/(800µA • 0.38Ω/°C • 200°C) 66 66 3507 191 Total Gain Error: 2000 100 2100 0 100 100 25µA/16000µA • 106 0.2µA/V • 5V/16000µA • 106 Total Output Error: 1563 63 1626 0 63 63 1.5µV/°C • 20°C/(800µA • 0.38Ω/°C • 200°C) • 106 20pA/°C • 20°C/800µA • 106 5pA/°C • 20°C • 100W/(800µA • 0.38Ω/°C • 200°C) • 106 35ppm/°C • 20°C 15ppm/°C • 20°C • 800µA • 100Ω/(800µA • 0.38Ω/°C • 200°C) 25ppm/°C • 20°C 0.5µA/°C • 20°C/16000µA • 106 Total Drift Error: 493 0.5 0.2 700 395 500 626 2715 493 0.5 0.2 700 395 500 626 2715 10 5 2 17 10 5 2 17 11728 (1.17%) 3168 (0.32%) 100µV/(800µA • 0.38Ω/°C • 200°C) • 106 50µV/V • 0.1V/(800µA • 0.38Ω/°C • 200°C) • 106 0.025µA/800µA • 106 3nA • 100Ω/(800µA • 0.38Ω/°C • 200°C) • 106 Total Input Error: Total Excitation Error: GAIN Span Nonlinearity OUTPUT Zero Output vs Supply Span Error (%)/100% • 106 Nonlinearity (%)/100% • 106 (IZERO – 4mA) /16000µA • 106 (IZERO vs V+) • ∆V+/16000µA • 106 DRIFT (∆TA = 20°C) Input Offset Voltage Drift • ∆TA/(VIN MAX) • 106 Input Bias Current (typical) Drift • ∆TA/800µA • 106 Input Offset Current (typical) Drift • ∆TA • RRTD MIN/(VIN MAX) • 106 Current Reference Accuracy Drift • ∆TA Current Reference Matching Drift • ∆TA • 800µA • RRTD MIN/(VIN MAX) Span Drift • ∆TA Zero Output Drift • ∆TA/16000µA • 106 NOISE (0.1Hz to 10Hz, typ) Input Offset Voltage Current Reference Zero Output 0.2%/100% • 106 0.01%/100% • 106 vn/(VIN MAX) • 106 IREF Noise • RRTD MIN/(VIN MAX) • 106 IZERO Noise/16000µA • 106 0.6µV/(800µA • 0.38Ω/°C • 200°C) • 106 3nA • 100Ω/(800µA • 0.38Ω/°C • 200°C) • 106 0.03µA/16000µA • 106 Total Noise Error: NOTE (1): All errors are min/max and referred to input unless otherwise stated. TOTAL ERROR: TABLE II. Error Calculation. XTR105 SBOS061B www.ti.com 11 REVERSE-VOLTAGE PROTECTION The XTR105’s low compliance rating (7.5V) permits the use of various voltage protection methods without compromising operating range. Figure 4 shows a diode bridge circuit that allows normal operation even when the voltage connection lines are reversed. The bridge causes a two diode drop (approximately 1.4V) loss in loop-supply voltage. This results in a compliance voltage of approximately 9V—satisfactory for most applications. If a 1.4V drop in loop supply is too much, a diode can be inserted in series with the loop-supply voltage and the V+ pin. This protects against reverse output connection lines with only a 0.7V loss in loop-supply voltage. SURGE PROTECTION Remote connections to current transmitters can sometimes be subjected to voltage surges. It is prudent to limit the maximum surge voltage applied to the XTR105 to as low as practical. Various zener diodes and surge clamping diodes are specially designed for this purpose. Select a clamp diode with as low a voltage rating as possible for best protection. For example, a 36V protection diode will assure proper transmitter operation at normal loop voltages, yet will provide an appropriate level of protection against voltage surges. Characterization tests on three production lots showed no damage to the XTR105 within loop-supply voltages up to 65V. Most surge protection zener diodes have a diode characteristic in the forward direction that will conduct excessive current, possibly damaging receiving-side circuitry if the loop connections are reversed. If a surge protection diode is used, a series diode or diode bridge should be used for protection against reversed connections. RADIO FREQUENCY INTERFERENCE The long wire lengths of current loops invite radio frequency (RF) interference. RF can be rectified by the sensitive input circuitry of the XTR105 causing errors. This generally appears as an unstable output current that varies with the position of loop supply or input wiring. If the RTD sensor is remotely located, the interference may enter at the input terminals. For integrated transmitter assemblies with short connections to the sensor, the interference more likely comes from the current loop connections. Bypass capacitors on the input reduce or eliminate this input interference. Connect these bypass capacitors to the IRET terminal (see Figure 5). Although the dc voltage at the IRET terminal is not equal to 0V (at the loop supply, VPS), this circuit point can be considered the transmitter’s “ground.” The 0.01µF capacitor connected between V+ and IO may help minimize output interference. NOTE: (1) Zener Diode 36V: 1N4753A or General Semiconductor TransorbTM 1N6286A. Use lower voltage zener diodes with loop-power supply voltages less than 30V for increased protection. See the Surge Protection section. 10 V+ 0.01µF XTR105 B E 9 D1(1) 1N4148 Diodes RL 8 IO 7 IRET 6 VPS Maximum VPS must be less than minimum voltage rating of zener diode. The diode bridge causes a 1.4V loss in loop-supply voltage. FIGURE 4. Reverse Voltage Operation and Over-Voltage Surge Protection. 12 XTR105 www.ti.com SBOS061B 12 1kΩ 13 4 RLIN1 VLIN + VIN 1 IR1 14 11 IR2 VREG 10 V+ RG RLIN2 RG B XTR105 3 E RG 9 0.01µF 8 IO 1kΩ 2 – VIN 7 IRET RZ 0.01µF 6 0.01µF RTD (1) RCM NOTE: (1) Bypass capacitors can be connected to either the IRET pin or the IO pin. 0.01µF FIGURE 5. Input Bypassing Technique with Linearization. IREG < 1mA 5V 12 V+ Type J VLIN 1/2 OPA2335 13 RF 10kΩ 4 R 412Ω + VIN 1 IR1 11 VREG XTR105 3 10 V+ RG RG 1250Ω RF 10kΩ 14 IR2 B E RG 9 8 IO 1/2 OPA2335 1kΩ 2 25Ω 7 IRET V– 50Ω – VIN 6 + – IO = 4mA + (VIN – VIN) 40 RG RCM = 1250Ω (G = 1 + 2RF = 50) R FIGURE 6. Thermocouple Low Offset, Low Drift Loop Measurement with Diode Cold Junction Compensation. XTR105 SBOS061B www.ti.com 13 12 13 4 1 IR1 VLIN + VIN 3 IR2 +12V 11 VREG 10 V+ 1µF RG B 9 RG 402Ω RLIN1 5760Ω 1N4148 14 XTR105 Q1 0.01µF 16 RG – VIN RTD RZ 137Ω 2 7 VO = 0 to 5V 14 13 5 4 IO = 4mA – 20mA 6 12 RCV420 IRET Pt100 100°C to 600°C 11 15 IO 2 10 3 E 8 1µF –12V RCM = 1kΩ NOTE: A 2-wire RTD connection is shown. For remotely located RTDs, a 3-wire RTD conection is recommended. RG becomes 383Ω, RLIN2 is 8060Ω. See Figure 3 and Table I. 0.01µF FIGURE 7. ±12V Powered Transmitter/Receiver Loop. 12 RLIN1 RLIN2 13 4 VLIN + VIN 1 IR1 1N4148 14 11 IR2 10 VREG V+ 0 RG RG 1µF XTR105 3 +15V 1µF B E RG 9 Q1 –15V 0.01µF 16 11 12 – 2 VIN IRET 2 7 IO = 4mA – 20mA 6 14 13 4 V+ 1 15 RCV420 IO RZ 10 3 8 Isolated Power from PWS740 9 15 ISO122 5 10 7 8 VO 0 – 5V 2 16 RTD NOTE: A 3-wire RTD connection is shown. For a 2-wire RTD connection eliminate RLIN2. V– RCM = 1kΩ 0.01µF FIGURE 8. Isolated Transmitter/Receiver Loop. 14 XTR105 www.ti.com SBOS061B 1.6mA 12 VLIN + 13 VIN 4 1 IR1 14 IR2 11 VREG 10 V+ RG RG XTR105 3 2 B E RG – VIN 9 8 7 IRET 6 RCM = 1kΩ(1) NOTE: (1) Use RCM to adjust the common-mode voltage to within 1.25V to 3.5V. FIGURE 9. Bridge Input, Current Excitation. XTR105 SBOS061B www.ti.com 15 PACKAGE OPTION ADDENDUM www.ti.com 16-Feb-2009 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Drawing Pins Package Eco Plan (2) Qty XTR105P ACTIVE PDIP N 14 25 Green (RoHS & no Sb/Br) CU NIPDAU N / A for Pkg Type XTR105PA ACTIVE PDIP N 14 25 Green (RoHS & no Sb/Br) CU NIPDAU N / A for Pkg Type XTR105PAG4 ACTIVE PDIP N 14 25 Green (RoHS & no Sb/Br) CU NIPDAU N / A for Pkg Type XTR105PG4 ACTIVE PDIP N 14 25 Green (RoHS & no Sb/Br) CU NIPDAU N / A for Pkg Type XTR105U ACTIVE SOIC D 14 50 Green (RoHS & no Sb/Br) CU NIPDAU Level-3-260C-168 HR XTR105UA ACTIVE SOIC D 14 50 Green (RoHS & no Sb/Br) CU NIPDAU Level-3-260C-168 HR XTR105UA/2K5 ACTIVE SOIC D 14 2500 Green (RoHS & no Sb/Br) CU NIPDAU Level-3-260C-168 HR XTR105UA/2K5E4 ACTIVE SOIC D 14 2500 Green (RoHS & no Sb/Br) CU NIPDAU Level-3-260C-168 HR XTR105UAG4 ACTIVE SOIC D 14 50 Green (RoHS & no Sb/Br) CU NIPDAU Level-3-260C-168 HR XTR105UG4 ACTIVE SOIC D 14 50 Green (RoHS & no Sb/Br) CU NIPDAU Level-3-260C-168 HR Lead/Ball Finish MSL Peak Temp (3) (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above. Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material) (3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. 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Addendum-Page 1 PACKAGE MATERIALS INFORMATION www.ti.com 23-May-2008 TAPE AND REEL INFORMATION *All dimensions are nominal Device XTR105UA/2K5 Package Package Pins Type Drawing SOIC D 14 SPQ Reel Reel Diameter Width (mm) W1 (mm) 2500 330.0 16.4 Pack Materials-Page 1 A0 (mm) B0 (mm) K0 (mm) P1 (mm) 6.5 9.0 2.1 8.0 W Pin1 (mm) Quadrant 16.0 Q1 PACKAGE MATERIALS INFORMATION www.ti.com 23-May-2008 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) XTR105UA/2K5 SOIC D 14 2500 346.0 346.0 33.0 Pack Materials-Page 2 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. 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