XTR106 XTR 106 X TR 1 06 SBOS092A – JUNE 1998 – REVISED NOVEMBER 2003 4-20mA CURRENT TRANSMITTER with Bridge Excitation and Linearization FEATURES APPLICATIONS ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● LOW TOTAL UNADJUSTED ERROR 2.5V, 5V BRIDGE EXCITATION REFERENCE 5.1V REGULATOR OUTPUT LOW SPAN DRIFT: ±25ppm/°C max LOW OFFSET DRIFT: 0.25µV/°C HIGH PSR: 110dB min HIGH CMR: 86dB min WIDE SUPPLY RANGE: 7.5V to 36V 14-PIN DIP AND SO-14 SURFACE-MOUNT PRESSURE BRIDGE TRANSMITTERS STRAIN GAGE TRANSMITTERS TEMPERATURE BRIDGE TRANSMITTERS INDUSTRIAL PROCESS CONTROL SCADA REMOTE DATA ACQUISITION REMOTE TRANSDUCERS WEIGHING SYSTEMS ACCELEROMETERS BRIDGE NONLINEARITY CORRECTION USING XTR106 DESCRIPTION 2.0 1.5 Nonlinearity (%) The XTR106 is a low cost, monolithic 4-20mA, twowire current transmitter designed for bridge sensors. It provides complete bridge excitation (2.5V or 5V reference), instrumentation amplifier, sensor linearization, and current output circuitry. Current for powering additional external input circuitry is available from the VREG pin. The instrumentation amplifier can be used over a wide range of gain, accommodating a variety of input signal types and sensors. Total unadjusted error of the complete current transmitter, including the linearized bridge, is low enough to permit use without adjustment in many applications. The XTR106 operates on loop power supply voltages down to 7.5V. Linearization circuitry provides second-order correction to the transfer function by controlling bridge excitation voltage. It provides up to a 20:1 improvement in nonlinearity, even with low cost transducers. The XTR106 is available in 14-pin plastic DIP and SO-14 surface-mount packages and is specified for the –40°C to +85°C temperature range. Operation is from –55°C to +125°C. Uncorrected Bridge Output 1.0 0.5 Corrected 0 –0.5 0 5 10 Bridge Output (mV) VREG (5.1V) VREF5 VREF 2.5V RLIN + 7.5V to 36V VPS 4-20mA 5V VO XTR106 RG RL – Lin Polarity IOUT IRET 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 © 1998-2003, 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 SPECIFICATIONS At TA = +25°C, V+ = 24V, and TIP29C external transistor, unless otherwise noted. XTR106P, U PARAMETER CONDITIONS OUTPUT Output Current Equation Output Current, Specified Range Over-Scale Limit Under-Scale Limit IO IOVER IUNDER ZERO OUTPUT(1) Initial Error vs Temperature vs Supply Voltage, V+ vs Common-Mode Voltage (CMRR) vs VREG (IO) Noise: 0.1Hz to 10Hz IZERO IO = VIN 4 24 1 2.9 • (40/RG) + 4mA, VIN in Volts, RG in Ω 20 ✻ 28 30 ✻ ✻ 1.6 2.2 ✻ ✻ 3.4 4 ✻ ✻ VIN = 0V, RG = ∞ 4 ±5 ±0.07 0.04 0.02 0.8 0.035 S VOS CMRR VCM IB Full Scale (VIN) = 50mV TA = –40°C to +85°C Full Scale (VIN) = 50mV S = 40/RG ±0.05 ±3 ±0.001 VCM = 2.5V TA = –40°C to +85°C V+ = 7.5V to 36V VCM = 1.1V to 3.5V(5) ±50 ±0.25 ±0.1 ±10 1.1 5 20 ±0.2 5 0.1 || 1 5 || 10 0.6 TA = –40°C to +85°C IOS TA = –40°C to +85°C ZIN Vn MAX MIN ✻ ✻ ✻ ✻ ✻ ✻ ✻ ±25 ±0.9 0.2 ✻ ✻ ✻ ✻ ±0.2 ±25 ±0.01 ±100 ±1.5 ±3 ±50 3.5 25 TYP ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ±3 MAX UNITS ✻ ✻ ✻ ✻ A mA mA mA mA ±50 ✻ ✻ ±0.4 ✻ ✻ ±250 ±3 ✻ ±100 ✻ 50 ±10 mA µA µA/°C µA/V µA/V µA/mA µAp-p A/V % ppm/°C % µV µV/°C µV/V µV/V V nA pA/°C nA pA/°C GΩ || pF GΩ || pF µVp-p Lin Polarity Connected to VREG, RLIN = 0 Initial: 2.5V Reference 5V Reference Accuracy vs Temperature vs Supply Voltage, V+ vs Load Noise: 0.1Hz to 10Hz VREF2.5 VREF5 VREG(5) Accuracy vs Temperature vs Supply Voltage, V+ Output Current Output Impedance VREG TA = –40°C to +85°C V+ = 7.5V to 36V IREG IREG = 0mA to 2.5mA RLIN KLIN Linearization Factor KLIN Accuracy vs Temperature Max Correctable Sensor Nonlinearity ±0.25 ±35 ±20 ✻ ✻ ✻ ✻ ✻ ✻ ✻ 5.1 ±0.02 ±0.1 ±0.3 1 See Typical Curves 80 ✻ ✻ ✻ ✻ ✻ ✻ 2.5 5 ±0.05 ±20 ±5 60 10 VREF = 2.5V or 5V TA = –40°C to +85°C V+ = 7.5V to 36V IREF = 0mA to 2.5mA LINEARIZATION(6) RLIN (external) Equation TEMPERATURE RANGE Specification Operating Storage Thermal Resistance 14-Pin DIP SO-14 Surface Mount TYP in VOLTAGE REFERENCES(5) POWER SUPPLY Specified Voltage Range MIN TA = –40°C to +85°C V+ = 7.5V to 36V VCM = 1.1V to 3.5V(5) SPAN Span Equation (Transconductance) Untrimmed Error vs Temperature(2) Nonlinearity: Ideal Input (3) INPUT(4) Offset Voltage vs Temperature vs Supply Voltage, V+ vs Common-Mode Voltage, RTI Common-Mode Range(5) Input Bias Current vs Temperature Input Offset Current vs Temperature Impedance: Differential Common-Mode Noise: 0.1Hz to 10Hz IREG = 0, IREF = 0 IREF + IREG = 2.5mA XTR106PA, UA B RLIN = KLIN • VREF = 5V VREF = 2.5V ✻ 4B , KLIN in Ω, B is nonlinearity relative to VFS 1 – 2B 6.645 9.905 ±1 ±50 ±5 –2.5, +5 TA = –40°C to +85°C VREF = 5V VREF = 2.5V ±0.5 ±75 ✻ ✻ ✻ ✻ ✻ ✻ ✻ ±5 ±100 ✻ ✻ V V % ppm/°C ppm/V ppm/mA µVp-p V V mV/°C mV/V mA Ω Ω kΩ kΩ % ppm/°C % of VFS % of VFS V+ ✻ +7.5 +24 +36 ✻ ✻ V V –40 –55 –55 +85 +125 +125 ✻ ✻ ✻ ✻ ✻ ✻ °C °C °C θJA 80 100 ✻ ✻ °C/W °C/W ✻ Specification same as XTR106P, XTR106U. NOTES: (1) Describes accuracy of the 4mA low-scale offset current. Does not include input amplifier effects. Can be trimmed to zero. (2) Does not include initial error or TCR of gain-setting resistor, RG. (3) Increasing the full-scale input range improves nonlinearity. (4) Does not include Zero Output initial error. (5) Voltage measured with respect to IRET pin. (6) See “Linearization” text for detailed explanation. VFS = full-scale VIN. 2 XTR106 www.ti.com SBOS092A ABSOLUTE MAXIMUM RATINGS(1) PIN CONFIGURATION Top View DIP and SOIC VREG 1 14 VREF5 V– IN 2 13 VREF2.5 RG 3 12 Lin Polarity RG 4 11 RLIN + VIN 5 10 V+ IRET 6 9 B (Base) IO 7 8 E (Emitter) Power Supply, V+ (referenced to IO pin) .......................................... 40V + – Input Voltage, VIN, VIN (referenced to IRET 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 NOTE: (1) Stresses above these ratings may cause permanent damage. Exposure to absolute maximum conditions for extended periods may degrade device reliability. ELECTROSTATIC DISCHARGE SENSITIVITY 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. PACKAGE/ORDERING INFORMATION For the most current package and ordering information, see the Package Option Addendum at the end of this data sheet. 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. XTR106 SBOS092A www.ti.com 3 FUNCTIONAL DIAGRAM VREG Lin Polarity 12 RLIN V+ 11 1 10 VREF5 VREF2.5 14 REF Amp Bandgap VREF 5.1V 13 Lin Amp Current Direction Switch + VIN 5 4 100µA B 9 RG 975Ω 25Ω 3 – VIN 2 I = 100µA + E VIN RG 8 7 6 IO = 4mA + VIN • ( 40 ) RG IRET 4 XTR106 www.ti.com SBOS092A TYPICAL PERFORMANCE CURVES At TA = +25°C, V+ = 24V, unless otherwise noted. TRANSCONDUCTANCE vs FREQUENCY RG = 50Ω 50 STEP RESPONSE CCOUT 0.01µF OUT==0.01µF COUT = 0.033µF COUT = 0.01µF RG = 1kΩ COUT connected between V+ and IO 40 30 20mA 4mA/div Transconductance (20 log mA/V) 60 RG = 1kΩ RG = 50Ω 20 4mA 10 RL = 250Ω 0 100 1k 10k 100k 1M 50µs/div Frequency (Hz) POWER SUPPLY REJECTION vs FREQUENCY 160 100 140 Power Supply Rejection (dB) Common-Mode Rejection (dB) COMMON-MODE REJECTION vs FREQUENCY 110 90 RG = 50Ω 80 RG = 1kΩ 70 60 50 120 100 RG = 1kΩ 80 60 40 20 40 0 30 10 100 1k 10k 100k 10 1M 100 1k 10k 100k Frequency (Hz) Frequency (Hz) INPUT OFFSET VOLTAGE DRIFT PRODUCTION DISTRIBUTION INPUT OFFSET VOLTAGE CHANGE vs VREG and VREF CURRENTS Typical production distribution of packaged units. 80 70 1M 1.5 90 VOS vs IREG 1.0 0.5 60 ∆ VOS (µV) Percent of Units (%) COUT = 0 RG = 50Ω 50 40 30 0 –0.5 VOS vs IREF –1.0 –1.5 20 –2.0 10 –2.5 –1.0 3.0 2.75 2.5 2.25 2.0 1.75 1.5 1.0 1.25 0.75 0.5 0.25 0 0 –0.5 0 0.5 1.0 1.5 2.0 2.5 Current (mA) Offset Voltage Drift (µV/°C) XTR106 SBOS092A www.ti.com 5 TYPICAL PERFORMANCE CURVES (CONT) At TA = +25°C, V+ = 24V, unless otherwise noted. UNDER-SCALE CURRENT vs TEMPERATURE UNDER-SCALE CURRENT vs IREF + IREG 4.0 2.5 Under-Scale Current (mA) Under-Scale Current (mA) 3.5 2.0 1.5 1.0 0.5 2.5 2.0 TA = +25°C 1.5 0.5 0 0 –75 –50 –25 0 25 50 75 100 0 125 0.5 1.0 1.5 2.0 Temperature (°C) IREF + IREG (mA) OVER-SCALE CURRENT vs TEMPERATURE ZERO OUTPUT ERROR vs VREF and VREG CURRENTS 2.5 3.0 30 With External Transistor 2.5 29 Zero Output Error (µA) Over-Scale Current (mA) TA = +125°C 1.0 V+ = 7.5V to 36V 28 V+ = 36V 27 V+ = 7.5V 26 V+ = 24V 25 2.0 IZERO Error vs IREG 1.5 1.0 0.5 IZERO Error vs IREF 0 –0.5 –1.0 24 –75 –50 –25 0 25 50 75 100 –1 125 –0.5 0 0.5 1.0 1.5 Temperature (°C) Current (mA) ZERO OUTPUT CURRENT ERROR vs TEMPERATURE ZERO OUTPUT DRIFT PRODUCTION DISTRIBUTION 4 70 2 60 0 Percent of Units (%) Zero Output Current Error (µA) TA = –55°C 3.0 –2 –4 –6 –8 2.0 2.5 Typical production distribution of packaged units. 50 40 30 20 10 –10 –12 0 –50 –25 0 25 50 75 100 125 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 –75 Temperature (°C) Zero Output Drift (µA/°C) 6 XTR106 www.ti.com SBOS092A TYPICAL PERFORMANCE CURVES (CONT) At TA = +25°C, V+ = 24V, unless otherwise noted. INPUT BIAS and OFFSET CURRENT vs TEMPERATURE INPUT VOLTAGE, INPUT CURRENT, and ZERO OUTPUT CURRENT NOISE DENSITY vs FREQUENCY Input Current Noise 100 100 Input Voltage Noise 10 1 10 100 1k 10k Input Bias and Offset Current (nA) 1k 1k Input Current Noise (fA/√Hz) Zero Output Noise Zero Output Current Noise (pA/√Hz) Input Voltage Noise (nV/√Hz) 10 10k 10k 8 IB 6 4 2 IOS 0 –2 10 100k –75 –50 –25 25 50 75 100 125 REFERENCE TRANSIENT RESPONSE VREF = 5V VREG OUTPUT VOLTAGE vs VREG OUTPUT CURRENT 50mV/div 5.5 Reference Output 5.6 5.4 5.3 5.2 TA = +25°C, –55°C 5.1 5.0 4.9 4.8 –1.0 TA = +125°C –0.5 0 0.5 1mA 500µA/div VREG Output Current (V) 0 Temperature (°C) Frequency (Hz) 1.0 1.5 2.0 0 2.5 10µs/div VREG Output Current (mA) REFERENCE AC LINE REJECTION vs FREQUENCY VREF5 vs VREG OUTPUT CURRENT 120 5.008 100 TA = +25°C Line Rejection (dB) VREF5 (V) 5.004 5.000 4.996 TA = +125°C 4.992 VREF2.5 80 60 VREF5 40 20 TA = –55°C 4.988 –1.0 0 –0.5 0 0.5 1.0 1.5 2.0 10 2.5 XTR106 SBOS092A 100 1k 10k 100k 1M Frequency (Hz) VREG Current (mA) www.ti.com 7 TYPICAL PERFORMANCE CURVES (CONT) At TA = +25°C, V+ = 24V, unless otherwise noted. REFERENCE VOLTAGE DEVIATION vs TEMPERATURE REFERENCE VOLTAGE DRIFT PRODUCTION DISTRIBUTION 40 30 25 20 15 10 5 Reference Voltage Deviation (%) Percent of Units (%) 35 0.1 Typical production distribution of packaged units. 0 0 –0.1 VREF = 5V –0.2 VREF = 2.5V –0.3 –0.4 –0.5 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 –75 –50 –25 0 25 50 75 100 125 Temperature (°C) Reference Voltage Drift (ppm/°C) 8 XTR106 www.ti.com SBOS092A APPLICATIONS INFORMATION The transfer function for the complete current transmitter is: IO = 4mA + VIN • (40/RG) Figure 1 shows the basic connection diagram for the XTR106. The loop power supply, VPS, provides power for all circuitry. Output loop current is measured as a voltage across the series load resistor, RL. A 0.01µF to 0.03µF supply bypass capacitor connected between V+ and IO is recommended. For applications where fault and/or overload conditions might saturate the inputs, a 0.03µF capacitor is recommended. where VIN is the differential input voltage. As evident from the transfer function, if no RG is used (RG = ∞), the gain is zero and the output is simply the XTR106’s zero current. 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 1.6mA. If current is being sourced from the reference and/or VREG, the current limit value may increase. Refer to the Typical Performance Curves, “Under-Scale Current vs IREF + IREG” and “UnderScale Current vs Temperature.” A 2.5V or 5V reference is available to excite a bridge sensor. For 5V excitation, pin 14 (VREF5) should be connected to the bridge as shown in Figure 1. For 2.5V excitation, connect pin 13 (VREF2.5) to pin 14 as shown in Figure 3b. The output terminals of the bridge are connected to the instrumentation amplifier inputs, VIN and VIN. A 0.01µF capacitor is shown + – connected between the inputs and is recommended for high impedance bridges (> 10kΩ). The resistor RG sets the gain of the instrumentation amplifier as required by the full-scale bridge voltage, VFS. Increasingly positive input voltage (greater than the fullscale input, VFS) will produce increasing output current according to the transfer function, up to the output current limit of approximately 28mA. Refer to the Typical Performance Curve, “Over-Scale Current vs Temperature.” Lin Polarity and RLIN provide second-order linearization correction to the bridge, achieving up to a 20:1 improvement in linearity. Connections to Lin Polarity (pin 12) determine the polarity of nonlinearity correction and should be connected either to IRET or VREG. Lin Polarity should be connected to VREG even if linearity correction is not desired. RLIN is chosen according to the equation in Figure 1 and is dependent on KLIN (linearization constant) and the bridge’s nonlinearity relative to VFS (see “Linearization” section). The IRET pin is the return path for all current from the references and VREG. IRET also serves as a local ground and is the reference point for VREG and the on-board voltage references. The IRET pin allows any current used in external circuitry to be sensed by the XTR106 and to be included in the output current without causing error. The input voltage range of the XTR106 is referred to this pin. For 2.5V excitation, connect VREG pin 13 to pin 14 VREF5 VREF2.5 Possible choices for Q1 (see text). RLIN(3) 14 13 5 11 RLIN 1 VREG + VIN CIN 0.01µF(2) 5V (5) R1(5) R2 + RB 4 3 2 PACKAGE TO-225 TO-220 TO-220 7.5V to 36V 10 V+ IO 4-20 mA (4) Bridge Sensor TYPE 2N4922 TIP29C TIP31C RG RG – (1) VIN in Volts, RG in Ohms B XTR106 E Lin(1) Polarity IRET Q1 COUT 0.01µF VO RG – VIN 9 + 8 RL IO VPS – 7 12 6 VREG(1) IO = 4mA + VIN • ( 40 ) RG or NOTES: (1) Connect Lin Polarity (pin 12) to IRET (pin 6) to correct for positive bridge nonlinearity or connect to VREG (pin 1) for negative bridge nonlinearity. The RLIN pin and Lin Polarity pin must be connected to VREG if linearity correction is not desired. Refer to “Linearization” section and Figure 3. (2) Recommended for bridge impedances > 10kΩ ( 3) RLIN = KLIN • 4B 1 – 2B (4) RG = (VFS/400µA) • 1 + 2B 1 – 2B (VFS in V) where KLIN = 9.905kΩ for 2.5V reference KLIN = 6.645kΩ for 5V reference B is the bridge nonlinearity relative to VFS VFS is the full-scale input voltage (5) R1 and R2 form bridge trim circuit to compensate for the initial accuracy of the bridge. See “Bridge Balance” text. (KLIN in Ω) FIGURE 1. Basic Bridge Measurement Circuit with Linearization. XTR106 SBOS092A www.ti.com 9 EXTERNAL TRANSISTOR External pass 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 XTR106, 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 XTR106 can be operated without an external pass transistor. Accuracy, however, 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 guarantee the full 20mA full-scale output, especially with V+ near 7.5V. The low operating voltage (7.5V) of the XTR106 allows operation directly from personal computer power supplies (12V ±5%). When used with the RCV420 Current Loop Receiver (Figure 8), load resistor voltage drop is limited to 3V. BRIDGE BALANCE Figure 1 shows a bridge trim circuit (R1, R2). This adjustment can be used to compensate for the initial accuracy of the bridge and/or to trim the offset voltage of the XTR106. The values of R1 and R2 depend on the impedance of the bridge, and the trim range required. This trim circuit places an additional load on the VREF output. Be sure the additional load on VREF does not affect zero output. See the Typical Performance Curve, “Under-Scale Current vs IREF + IREG.” The effective load of the trim circuit is nearly equal to R2. An approximate value for R1 can be calculated: R1 ≈ (3) 5V • R B 4 • V TRIM where, RB is the resistance of the bridge. VTRIM is the desired ±voltage trim range (in V). Make R2 equal or lower in value to R1. LINEARIZATION Many bridge sensors are inherently nonlinear. With the addition of one external resistor, it is possible to compensate for parabolic nonlinearity resulting in up to 20:1 improvement over an uncompensated bridge output. 10 V+ E 8 XTR106 0.01µF IO 7 IRET 6 RQ = 3.3kΩ For operation without external transistor, connect a 3.3kΩ resistor between pin 6 and pin 8. See text for discussion of performance. FIGURE 2. Operation without External Transistor. LOOP POWER SUPPLY The voltage applied to the XTR106, 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 XTR106 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: R L max = (V+) – 7. 5V – R WIRING 20mA (2) It is recommended to design for V+ equal or greater than 7.5V with loop currents up to 30mA to allow for out-ofrange input conditions. V+ must be at least 8V if 5V sensor excitation is used and if correcting for bridge nonlinearity greater than +3%. 10 Linearity correction is accomplished by varying the bridge excitation voltage. Signal-dependent variation of the bridge excitation voltage adds a second-order term to the overall transfer function (including the bridge). This can be tailored to correct for bridge sensor nonlinearity. Either positive or negative bridge non-linearity errors can be compensated by proper connection of the Lin Polarity pin. To correct for positive bridge nonlinearity (upward bowing), Lin Polarity (pin 12) should be connected to IRET (pin 6) as shown in Figure 3a. This causes VREF to increase with bridge output which compensates for a positive bow in the bridge response. To correct negative nonlinearity (downward bowing), connect Lin Polarity to VREG (pin 1) as shown in Figure 3b. This causes VREF to decrease with bridge output. The Lin Polarity pin is a high impedance node. If no linearity correction is desired, both the RLIN and Lin Polarity pins should be connected to VREG (Figure 3c). This results in a constant reference voltage independent of input signal. RLIN or Lin Polarity pins should not be left open or connected to another potential. RLIN is the external linearization resistor and is connected between pin 11 and pin 1 (VREG) as shown in Figures 3a and 3b. To determine the value of RLIN, the nonlinearity of the bridge sensor with constant excitation voltage must be known. The XTR106’s linearity circuitry can only compensate for the parabolic-shaped portions of a sensor’s nonlinearity. Optimum correction occurs when maximum deviation from linear output occurs at mid-scale (see Figure 4). Sensors with nonlinearity curves similar to that shown in XTR106 www.ti.com SBOS092A Figure 4, but not peaking exactly at mid-scale can be substantially improved. A sensor with a “S-shaped” nonlinearity curve (equal positive and negative nonlinearity) cannot be improved with the XTR106’s correction circuitry. The value of RLIN is chosen according to Equation 4 shown in Figure 3. RLIN is dependent on a linearization factor, KLIN, which differs for the 2.5V reference and 5V reference. The sensor’s nonlinearity term, B (relative to full scale), is positive or negative depending on the direction of the bow. A maximum ±5% non-linearity can be corrected when the 5V reference is used. Sensor nonlinearity of +5%/–2.5% can be corrected with 2.5V excitation. The trim circuit shown in Figure 3d can be used for bridges with unknown bridge nonlinearity polarity. Gain is affected by the varying excitation voltage used to correct bridge nonlinearity. The corrected value of the gain resistor is calculated from Equation 5 given in Figure 3. VREG VREF5 XTR106 VREF2.5 14 5 5V R2 Lin Polarity RLIN 13 1 + IRET 11 R1 + – RG 2 RY RX 100kΩ 15kΩ Open RX for negative bridge nonlinearity Open RY for positive bridge nonlinearity XTR106 – 3d. On-Board Resistor Circuit for Unknown Bridge Nonlinearity Polarity 12 6 Lin Polarity IRET EQUATIONS Linearization Resistor: 3a. Connection for Positive Bridge Nonlinearity, VREF = 5V VREG RLIN = KLIN • VREF2.5 VREF5 RLIN 13 5 2.5V 1 + 11 4 – RG RG = VFS 400µA 1 + 2B 1 – 2B (in Ω) (5) 1 + 2B 1 – 2B (in V) (6) KLIN = 9905Ω for the 2.5V reference – 12 KLIN = 6645Ω for the 5V reference Lin Polarity B is the sensor nonlinearity relative to VFS (for –2.5% nonlinearity, B = –0.025) IRET VFS is the full-scale bridge output without linearization (in V) 3b. Connection for Negative Bridge Nonlinearity, VREF = 2.5V Example: VREG VREF5 Calculate RLIN and the resulting RG for a bridge sensor with 2.5% downward bow nonlinearity relative to VFS and determine if the input common-mode range is valid. VREF2.5 14 RLIN 13 5V (4) where, KLIN is the linearization factor (in Ω) 6 5 • VREF (Adj) = VREF (Initial) • XTR106 3 2 (in Ω) Adjusted Excitation Voltage at Full-Scale Output: R1 + 4B 1– 2B Gain-Set Resistor: 14 R2 1 12 6 4 3 R2 VREG 1 + VREF = 2.5V and VFS = 50mV 11 For a 2.5% downward bow, B = –0.025 (Lin Polarity pin connected to VREG) 4 For VREF = 2.5V, KLIN = 9905Ω R1 + – RG XTR106 RLIN = 3 2 RG = – 12 6 Lin Polarity VCM = IRET 3c. Connection if no linearity correction is desired, VREF = 5V (9905Ω) (4) ( –0.025) = 943Ω 1 – (2) ( –0.025) 0.05V 1 + (2) ( –0.025) • = 113Ω 400µA 1 – (2) ( –0.025) VREF (Adj) 2 = 1 1 + (2) ( –0.025) • 2.5V • = 1.13V 2 1 – (2) ( –0.025) which falls within the 1.1V to 3.5V input common-mode range. FIGURE 3. Connections and Equations to Correct Positive and Negative Bridge Nonlinearity. XTR106 SBOS092A www.ti.com 11 UNDER-SCALE CURRENT When using linearity correction, care should be taken to insure that the sensor’s output common-mode voltage remains within the XTR106’s allowable input range of 1.1V to 3.5V. Equation 6 in Figure 3 can be used to calculate the XTR106’s new excitation voltage. The common-mode voltage of the bridge output is simply half this value if no common-mode resistor is used (refer to the example in Figure 3). Exceeding the common-mode range may yield unpredicatable results. The total current being drawn from the VREF and VREG voltage sources, as well as temperature, affect the XTR106’s under-scale current value (see the Typical Performance Curve, “Under-Scale Current vs IREF + IREG). This should be considered when choosing the bridge resistance and excitation voltage, especially for transducers operating over a wide temperature range (see the Typical Performance Curve, “Under-Scale Current vs Temperature”). For high precision applications (errors < 1%), a two-step calibration process can be employed. First, the nonlinearity of the sensor bridge is measured with the initial gain resistor and RLIN = 0 (RLIN pin connected directly to VREG). Using the resulting sensor nonlinearity, B, values for RG and RLIN are calculated using Equations 4 and 5 from Figure 3. A second calibration measurement is then taken to adjust RG to account for the offsets and mismatches in the linearization. LOW IMPEDANCE BRIDGES The XTR106’s two available excitation voltages (2.5V and 5V) allow the use of a wide variety of bridge values. Bridge impedances as low as 1kΩ can be used without any additional circuitry. Lower impedance bridges can be used with the XTR106 by adding a series resistance to limit excitation current to ≤ 2.5mA (Figure 5). Resistance should be added BRIDGE TRANSDUCER TRANSFER FUNCTION WITH PARABOLIC NONLINEARITY NONLINEARITY vs STIMULUS 10 3 Nonlinearity (% of Full Scale) 9 Bridge Output (mV) 8 Positive Nonlinearity B = +0.025 7 6 5 4 B = –0.019 Negative Nonlinearity 3 2 Linear Response 2 Positive Nonlinearity B = +0.025 1 0 –1 –2 Negative Nonlinearity B = –0.019 1 0 –3 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Normalized Stimulus 0.8 0.9 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Normalized Stimulus 0.8 0.9 1 FIGURE 4. Parabolic Nonlinearity. 700µA at 5V VREF5 ITOTAL = 0.7mA + 1.6mA ≤ 2.5mA IREG ≈ 1.6mA VREF2.5 VREG 3.4kΩ 14 13 5V 1/2 OPA2277 1kΩ 5 1 RLIN 1N4148 11 V+IN 10 V+ 4 RG 10kΩ 350Ω RG 125Ω 412Ω 10kΩ 3.4kΩ 1/2 OPA2277 3 2 B 9 XTR106 E RG V Lin I O Polarity – IN 0.01µF IRET 8 7 12 6 IO = 4-20mA Bridge excitation voltage = 0.245V Shown connected to correct positive bridge nonlinearity. For negative bridge nonlinearity, see Figure 3b. Approx. x50 amplifier FIGURE 5. 350Ω Bridge with x50 Preamplifier. 12 XTR106 www.ti.com SBOS092A to the upper and lower sides of the bridge to keep the bridge output within the 1.1V to 3.5V common-mode input range. Bridge output is reduced so a preamplifier as shown may be needed to reduce offset voltage and drift. OTHER SENSOR TYPES The XTR106 can be used with a wide variety of inputs. Its high input impedance instrumentation amplifier is versatile and can be configured for differential input voltages from millivolts to a maximum of 2.4V full scale. The linear range of the inputs is from 1.1V to 3.5V, referenced to the IRET terminal, pin 6. The linearization feature of the XTR106 can be used with any sensor whose output is ratiometric with an excitation voltage. ERROR ANALYSIS Table I shows how to calculate the effect various error sources have on circuit accuracy. A sample error calculation for a typical bridge sensor measurement circuit is shown (5kΩ bridge, VREF = 5V, VFS = 50mV) is provided. The results reveal the XTR106’s excellent accuracy, in this case 1.2% unadjusted. Adjusting gain and offset errors improves circuit accuracy to 0.33%. Note that these are worst-case errors; guaranteed maximum values were used in the calculations and all errors were assumed to be positive (additive). The XTR106 achieves performance which is difficult to obtain with discrete circuitry and requires less board space. SAMPLE ERROR CALCULATION Bridge Impedance (RB) Ambient Temperature Range (∆TA) Supply Voltage Change (∆V+) Full Scale Input (VFS) Excitation Voltage (VREF) Common-Mode Voltage Change (∆CM) INPUT Input Offset Voltage vs Common-Mode vs Power Supply Input Bias Current Input Offset Current ERROR CALCULATION VOS /VFS • 106 CMRR • ∆CM/VFS • 106 (VOS vs V+) • (∆V+)/VFS • 106 CMRR • IB • (RB /2)/ VFS • 106 IOS • RB /VFS • 106 EXCITATION Voltage Reference Accuracy vs Supply VREF Accuracy (%)/100% • 106 (VREF vs V+) • (∆V+) • (VFS/VREF) GAIN Span Nonlinearity Span Error (%)/100% • 106 Nonlinearity (%)/100% • 106 OUTPUT Zero Output vs Supply UNADJ ADJUST 200µV/50mV • 106 50µV/V • 0.025V/50mV • 106 3µV/V • 5V/50mV • 106 50µV/V • 25nA • 2.5kΩ/50mV • 106 3nA • 5kΩ/50mV • 106 Total Input Error 2000 25 300 0.1 300 2625 0 25 300 0 0 325 0.25%/100% • 106 20ppm/V • 5V (50mV/5V) Total Excitation Error 2500 1 2501 0 1 1 Total Gain Error 2000 100 2100 0 100 100 25µA/16000µA • 106 0.2µA/V • 5V/16000µA • 106 Total Output Error 1563 62.5 1626 0 62.5 63 1.5µV / °C • 20°C / (50mV) • 106 5pA / °C • 20°C • 5kΩ/ (50mV) • 106 35ppm/°C • 20°C 225ppm/°C • 20°C 0.9µA /°C • 20°C / 16000µA • 106 Total Drift Error 600 10 700 500 1125 2936 600 10 700 500 1125 2936 12 2.2 0.6 0.6 15 12 2.2 0.6 0.6 15 0.2%/100% • 106 0.01%/100% • 106 | IZERO – 4mA | /16000µA • 106 (IZERO vs V+) • (∆V+)/16000µA • 106 DRIFT (∆TA = 20°C) Input Offset Voltage Input Offset Current (typical) Voltage Refrence Accuracy Span Zero Output 50mV 5V 25mV (= VFS/2) ERROR (ppm of Full Scale) SAMPLE ERROR EQUATION ERROR SOURCE NOISE (0.1Hz to 10Hz, typ) Input Offset Voltage Zero Output Thermal RB Noise Input Current Noise 5kΩ 20°C 5V Drift • ∆TA / (VFS) • 106 Drift • ∆TA • RB / (VFS) • 106 Drift • ∆TA / 16000µA • 106 Vn(p-p)/ VFS • 106 IZERO Noise / 16000µA • 106 [√ 2 • √ (RB / 2 ) / 1kΩ • 4nV / √ Hz • √ 10Hz ] / VFS • 106 (in • 40.8 • √2 • RB / 2)/ VFS • 106 0.6µV / 50mV • 106 0.035µA / 16000µA • 106 [√ 2 • √ 2.5kΩ / 1kΩ • 4nV/ √ Hz • √ 10Hz ] / 50mV • 106 (200fA/√Hz • 40.8 • √2 • 2.5kΩ)/50mV• 106 Total Noise Error NOTE (1): All errors are min/max and referred to input, unless otherwise stated. TOTAL ERROR: 11803 1.18% 3340 0.33% TABLE I. Error Calculation. XTR106 SBOS092A www.ti.com 13 REVERSE-VOLTAGE PROTECTION The XTR106’s low compliance rating (7.5V) permits the use of various voltage protection methods without compromising operating range. Figure 6 shows a diode bridge circuit which 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. A diode can be inserted in series with the loop supply voltage and the V+ pin as shown in Figure 8 to protect against reverse output connection lines with only a 0.7V loss in loop supply voltage. OVER-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 XTR106 to as low as practical. Various zener diode 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 XTR106 with loop supply voltages up to 65V. VREF5 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 interference. RF can be rectified by the sensitive input circuitry of the XTR106 causing errors. This generally appears as an unstable output current that varies with the position of loop supply or input wiring. If the bridge sensor is remotely located, the interference may enter at the input terminals. For integrated transmitter assemblies with short connection 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 as shown in Figure 6. 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. VREF2.5 14 13 5 + VIN 4 5V + RB – RG RG XTR106 3 Bridge Sensor Maximum VPS must be less than minimum voltage rating of zener diode. 10 V+ B E RG 9 Q1 0.01µF D1(1) 1N4148 Diodes RL 8 VPS IO 2 – VIN The diode bridge causes a 1.4V loss in loop supply voltage. 7 IRET 6 0.01µF 0.01µF NOTE: (1) Zener Diode 36V: 1N4753A or Motorola P6KE39A. Use lower voltage zener diodes with loop power supply voltages less than 30V for increased protection. See “Over-Voltage Surge Protection.” FIGURE 6. Reverse Voltage Operation and Over-Voltage Surge Protection. 14 XTR106 www.ti.com SBOS092A VREF5 0.01µF See ISO124 data sheet if isolation is needed. 1MΩ VREF2.5 4.8kΩ 6kΩ Isothermal Block 14 20kΩ OPA277 5 + 13 11 RLIN VIN 7.5V to 36V 1 VREG 4 Type K 1N4148 IO 4-20 mA XTR106 3 V+ RG RG 1kΩ 1MΩ(1) 10 E RG Lin Polarity – 2 VIN IRET 9 COUT 0.01µF Q1 VO 8 + VPS – RL IO 7 12 IO = 4mA + VIN • ( 40 ) RG 6 5.2kΩ 50Ω B VREG (pin 1) 100Ω 2kΩ NOTE: (1) For burn-out indication. 0.01µF FIGURE 7. Thermocouple Low Offset, Low Drift Loop Measurement with Diode Cold-Junction Compensation. VREF2.5 Bridge Sensor VREG VREF5 2.5V 14 RLIN 13 1 RB 5 VIN + 4 +12V 10 V+ B XTR106 2 1µF RG RG 3 1N4148 11 + – See ISO124 data sheet if isolation is needed. RG E Lin Polarity – VIN IRET 9 0.01µF 16 10 3 8 11 12 15 IO RCV420 2 7 VO = 0V to 5V 13 5 12 6 14 4 1µF IO = 4-20mA NOTE: Lin Polarity shown connected to correct positive bridge nonlinearity. See Figure 3b to correct negative bridge nonlinearity. –12V FIGURE 8. ±12V-Powered Transmitter/Receiver Loop. XTR106 SBOS092A 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 XTR106P ACTIVE PDIP N 14 25 Green (RoHS & no Sb/Br) CU NIPDAU N / A for Pkg Type XTR106PA ACTIVE PDIP N 14 25 Green (RoHS & no Sb/Br) CU NIPDAU N / A for Pkg Type XTR106PAG4 ACTIVE PDIP N 14 25 Green (RoHS & no Sb/Br) CU NIPDAU N / A for Pkg Type XTR106PG4 ACTIVE PDIP N 14 25 Green (RoHS & no Sb/Br) CU NIPDAU N / A for Pkg Type XTR106U ACTIVE SOIC D 14 50 Green (RoHS & no Sb/Br) CU NIPDAU Level-3-260C-168 HR XTR106U/2K5 ACTIVE SOIC D 14 2500 Green (RoHS & no Sb/Br) CU NIPDAU Level-3-260C-168 HR XTR106U/2K5E4 ACTIVE SOIC D 14 2500 Green (RoHS & no Sb/Br) CU NIPDAU Level-3-260C-168 HR XTR106UA ACTIVE SOIC D 14 Green (RoHS & no Sb/Br) CU NIPDAU Level-3-260C-168 HR XTR106UA/2K5 ACTIVE SOIC D 14 2500 Green (RoHS & no Sb/Br) CU NIPDAU Level-3-260C-168 HR XTR106UA/2K5E4 ACTIVE SOIC D 14 2500 Green (RoHS & no Sb/Br) CU NIPDAU Level-3-260C-168 HR XTR106UAG4 ACTIVE SOIC D 14 50 Green (RoHS & no Sb/Br) CU NIPDAU Level-3-260C-168 HR XTR106UE4 ACTIVE SOIC D 14 50 Green (RoHS & no Sb/Br) CU NIPDAU Level-3-260C-168 HR 50 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. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals. TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release. Addendum-Page 1 PACKAGE OPTION ADDENDUM www.ti.com 16-Feb-2009 In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis. Addendum-Page 2 PACKAGE MATERIALS INFORMATION www.ti.com 11-Mar-2008 TAPE AND REEL INFORMATION *All dimensions are nominal Device Package Package Pins Type Drawing SPQ Reel Reel Diameter Width (mm) W1 (mm) A0 (mm) B0 (mm) K0 (mm) P1 (mm) W Pin1 (mm) Quadrant XTR106U/2K5 SOIC D 14 2500 330.0 16.4 6.5 9.0 2.1 8.0 16.0 Q1 XTR106UA/2K5 SOIC D 14 2500 330.0 16.4 6.5 9.0 2.1 8.0 16.0 Q1 Pack Materials-Page 1 PACKAGE MATERIALS INFORMATION www.ti.com 11-Mar-2008 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) XTR106U/2K5 SOIC D 14 2500 346.0 346.0 33.0 XTR106UA/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. 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