XTR104BP

® XTR104 4-20mA Current Transmitter with BRIDGE EXCITATION AND LINEARIZATION FEATURES APPLICATIONS ● LESS THAN ±1% TOTAL ADJUSTED ERROR, –40°C TO +85°C ● INDUSTRIAL PROCESS CONTROL ● FACTORY AUTOMATION ● BRIDGE EXCITATION AND LINEARIZATION ● WIDE SUPPLY RANGE: 9V to 40V ● LOW SPAN DRIFT: 50ppm/°C max ● SCADA ● WEIGHTING SYSTEMS ● ACCELEROMETERS ● HIGH PSR: 110dB min ● HIGH CMR: 80dB min BRIDGE NONLINEARITY CORRECTION USING XTR104 2.0 DESCRIPTION Uncorrected Bridge Output 1.5 Nonlinearity (%) The XTR104 is a monolithic 4-20mA, two-wire current transmitter integrated circuit designed for bridge input signals. It provides complete bridge excitation, instrumentation amplifier, linearization, and current output circuitry necessary for high impedance strain gage sensors. The instrumentation amplifier can be used over a wide range of gain, accommodating a variety of input signals and sensors. Total adjusted error of the complete current transmitter, including the linearized bridge is less than ±1% over the full –40°C to +85°C temperature range. This includes zero drift, span drift and non-linearity for bridge outputs as low as 10mV. The XTR104 operates on loop power supply voltages down to 9V. Linearization circuitry consists of a second, fully independent instrumentation amplifier that controls the bridge excitation voltage. It provides second-order correction to the transfer function, typically achieving a 20:1 improvement in nonlinearity, even with low cost transducers. The XTR104 is available in 16-pin plastic DIP and SOL-16 surface-mount packages specified for the –40°C to +85°C temperature range. 1.0 0.5 Corrected 0 –0.5 0mV 5mV 10mV Bridge Output + R LIN 9V to 40V VPS 4-20 mA XTR104 RG VO RL – International Airport Industrial Park • Mailing Address: PO Box 11400 • Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd. • Tucson, AZ 85706 Tel: (520) 746-1111 • Twx: 910-952-1111 • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132 ® © SBOS018 1992 Burr-Brown Corporation PDS-1146B 1 XTR104 Printed in U.S.A. September, 1993 SPECIFICATIONS TA = +25°C, V+ = 24V, and 2N6121 external transistor, unless otherwise noted. XTR104BP, BU PARAMETER CONDITIONS OUTPUT Output Current Equation Total Adjusted Error (1) Current, Specified Range Over-Scale Limit Under Scale-Limit Full Scale Output Error Noise: 0.1Hz to 1kHz ZERO OUTPUT(2) Initial Error vs Temperature vs Supply Voltage, V+ vs Common-Mode Voltage SPAN Span Equation (Transconductance) Untrimmed Error vs Temperature(4) Nonlinearity: Ideal Input Bridge Input (5) INPUT Differential Range Input Voltage Range(3) Common-Mode Rejection Impedance: Differential Common-Mode Offset Voltage vs Temperature vs Supply Voltage, V+ Input Bias Current vs Temperature Input Offset Current vs Temperature VOLTAGE REFERENCE(6) Voltage Accuracy vs Temperature vs Supply Voltage, V+ vs Load MIN VIN = 1V, RG = ∞ RG = 40Ω VIN = 0V, RG = ∞ 4 ±5 ±0.2 0.5 0.1 V+ = 9V to 40V(3) VCM = 2V to 3V(3) 2 80 110 V+ = 9V to 40V(3) IL = 0 to 2mA (TMIN to TMAX) Derated Performance TYP * * * * * ±50 ±0.5 2 2 1 3 100 3 0.5 ±0.5 1 130 100 0.1 2 0.01 5 ±0.25 ±10 5 50 POWER SUPPLY Voltage Range(3), V+ TEMPERATURE RANGE Specification Operating θJA MIN * * * S = 0.016 + 40/RG ±0.1 ±1 ±20 ±50 0.01 0.1 RG ≥ 75Ω V+ = 9V to 40V(3) XTR104AP, AU MAX MAX IO = VIN • (0.016 + 40/RG) + 4mA VIN in Volts, RG in Ω ±1 ±2 4 20 * * 34 40 * * 3.6 3.8 * * ±15 ±50 * ±100 8 * TMIN to TMAX, VFS ≥ 10mV, RB = 5kΩ VIN = 2V to 3V (3) TYP mA µA µA/°C µA/V µA/V * ±100 * A/V % ppm/°C % % ±2.5 2.5 * 250 2 20 0.25 * * * * * * 2 * * * * * * * * * * ±0.5 ±50 A % of FS mA mA mA µA µAp-p ±100 ±1 * * * * * UNITS * 5 * * * * ±1 ±100 V V dB GΩ GΩ mV µV/°C dB nA nA/°C nA nA/°C V % ppm/°C ppm/V ppm/mA 9 40 * * V –40 –40 85 125 * * * * °C °C °C/W 80 * * Specification same as XTR104BP. NOTES: (1) Includes corrected second-order nonlinearity of bridge, and over-temperature zero and span effects. Does not include initial offset and span errors which are normally trimmed to zero at 25°C. (2) Describes accuracy of the 4mA low-scale current. Does not include input amplifier effects. Can be trimmed to zero. (3) Voltage measured with respect to IO pin. (4) Does not include TCR of gain-setting resistor, RG. (5) When configured to correct for ≤2% second-order bridge sensor nonlinearity. (6) Measured with RLIN = ∞ to disable linearization feature. ® XTR104 2 PIN CONFIGURATION ABSOLUTE MAXIMUM RATINGS Top View Power Supply, V+ (referenced to IO pin) .......................................... 40V Input Voltage, V+IN , V–IN, V+LIN , V– LIN (referenced to 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 DIP V+IN 1 16 Zero Adjust V– 2 15 Zero Adjust V+LIN 3 14 Zero Adjust V–LIN 4 13 B (Base) RG 5 12 VREF RG 6 11 E (Emitter) IO 7 10 V+ RLIN 8 9 IN PACKAGE INFORMATION MODEL XTR104AP XTR104BP XTR104AU XTR104BU RLIN PACKAGE 16-Pin Plastic 16-Pin Plastic SOL-16 Surface SOL-16 Surface PACKAGE DRAWING NUMBER(1) DIP DIP Mount Mount 180 180 211 211 NOTE: (1) For detailed drawing and dimension table, please see end of data sheet, or Appendix D of Burr-Brown IC Data Book. ORDERING INFORMATION MODEL PACKAGE XTR104AP XTR104BP XTR104AU XTR104BU 16-pin Plastic 16-pin Plastic SOL-16 Surface SOL-16 Surface DIP DIP Mount Mount TEMPERATURE RANGE –40°C –40°C –40°C –40°C to to to to +85°C +85°C +85°C +85°C ELECTROSTATIC DISCHARGE SENSITIVITY Electrostatic discharge can cause damage ranging from performance degradation to complete device failure. Burr-Brown Corporation recommends that all integrated circuits be handled and stored using appropriate ESD protection methods. 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 published specifications. The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes no responsibility for the use of this information, and all use of such information shall be entirely at the user’s own risk. Prices and specifications are subject to change without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant any BURR-BROWN product for use in life support devices and/or systems. ® 3 XTR104 DICE INFORMATION PAD FUNCTION PAD FUNCTION 1 2 3 4 5 6 7 8 V+IN V–IN V+LIN V–LIN RG RG IO RLIN 9 10 11 12A, 12B 13 14 15 16 RLIN V+ E (Emitter) VREF B (Base) Zero Adj. Zero Adj. Zero Adj. Pads 12A and 12B must be connected. NC: No Connection Substrate Bias: Internally connected to the IO terminal (#7). FPO MECHANICAL INFORMATION Die Size Die Thickness Min. Pad Size MILS (0.001") MILLIMETERS 168 x 104 ±5 20 ±3 4x4 4.27 x 2.64 ±0.13 0.51 ±0.08 0.1 x 0.1 Backing XTR104 DIE TOPOGRAPHY None TYPICAL PERFORMANCE CURVES TA = +25°C, V+ = 24V, unless otherwise noted. TRANSCONDUCTANCE vs FREQUENCY STEP RESPONSE 60 RG = ∞ RG = 25Ω RG = 100Ω 40 20mA RG = 400Ω RG = 25Ω RG = 2kΩ RG = ∞ 20 4mA 0 100 1k 10k 100k 100µs/Div 1M Frequency (Hz) ® XTR104 4 5mA/Div Transconductance (20 Log mA/V) 80 TYPICAL PERFORMANCE CURVES (CONT) TA = +25°C, +V = 24V, unless otherwise noted. POWER SUPPLY REJECTION vs FREQUENCY (RTI) COMMON-MODE REJECTION vs FREQUENCY (RTI) 120 140 Power Supply Rejection (dB) G = 0.16A/V (RG = 400Ω) 100 CMR (dB) 80 60 40 20 G = 0.16A/V (RG = 400Ω) 120 100 80 60 40 20 0 0 0.1 1 10 100 1k 10k 0.1 100k 1 10 LOOP RESISTANCE vs LOOP POWER SUPPLY 1750 Output Current Noise (pA/ Hz) 1000 750 Operating Region 250 9V 0 100k RG = ∞ 1 0.1 0 10 20 30 40 50 0.1 1 10 Loop Power Supply Voltage, VPS (V) 100 1k 10k 100k Frequency (Hz) INPUT CURRENT NOISE DENSITY vs FREQUENCY INPUT VOLTAGE NOISE DENSITY vs FREQUENCY 1k Noise Voltage (nV/ Hz ) 10 Input Current Noise (pA/ Hz ) Loop Resistance, RL (Ω ) (V+) – 9V 20mA 500 10k OUTPUT CURRENT NOISE DENSITY vs FREQUENCY 1500 R max = 1k 10 1550Ω 1250 100 Frequency (Hz) Frequency (Hz) 1 0.1 100 10 0.1 1 10 100 1k 10k 100k 0.1 Frequency (Hz) 1 10 100 1k 10k 100k Frequency (Hz) ® 5 XTR104 APPLICATION INFORMATION EXTERNAL TRANSISTOR Transistor Q1 conducts the majority of the signal-dependent 4 to 20mA loop current. Using an external transistor isolates the power dissipation from the precision input and reference circuitry of the XTR104, maintaining excellent accuracy. Figure 1 shows the basic connection diagram for the XTR104. The loop power supply, VPS, provides power for all circuitry. Loop current is measured as a voltage across the series load resistor, RL. Since the external transistor is inside a feedback loop its characteristics are not critical. Many common NPN types can be used. Requirements for operation at the full loop supply voltage are: VCEO = 45V min, β = 40 min and PD = 800mW. Power dissipation requirements may be lower if the maximum loop power supply voltage is less than 40V. Some possible choices for Q1 are listed in Figure 1. A high impedance (≥2750Ω) strain gage sensor can be excited directly by the 5V reference output terminal, VR. The output terminals of the bridge are connected to the instrumentation amplifier inputs, V+IN and V–IN. The resistor, RG, sets the gain of the instrumentation amplifier as required by the full-scale bridge voltage, VFS. The transfer function is: (1) IO = VIN • (0.016 + 40/RG) + 4mA, LOOP POWER SUPPLY The voltage applied to the XTR104, V+, is measured with respect to the IO connection, pin 7. V+ can range from 9V to 40V. The loop supply voltage, VPS, will differ from the voltage applied to the XTR104 according to the voltage drop on the current sensing resistor, RL (plus any other voltage drop in the line). V+ Where: VIN is the voltage applied to the IN and V–IN differential inputs (in Volts.) RG in Ω. With no RG connected (RG = ∞), a 0V to 1V input produces a 4 to 20mA output current. With RG = 25Ω, a 0V to 10mV input produces a 4 to 20mA output current. Other values for RG can be calculated as follows: 2500 1 –1 VFS RG = If a low loop supply voltage is used, RL must be made a relatively low value to assure that V+ remains 9V or greater for the maximum loop current of 20mA. It may, in fact, be prudent to design for V+ equal or greater than 9V with loop currents up to 34mA to allow for out-of-range input conditions. The typical performance curve “Loop Resistance vs Loop Power Supply” shows the allowable sense resistor values for full-scale 20mA. (2) Where: VFS is the full scale voltage applied to the V+IN and V–IN differential inputs (in Volts). RG in Ω. Under-scale input voltage (negative) will cause the output current to decrease below 4mA. Increasingly negative input will cause the output current to limit at approximately 3.6mA. The low operating voltage (9V) of the XTR104 allows operation directly from personal computer power supplies (12V±5%). When used with the RCV420 Current Loop Receiver (see Figure 9), load resistor voltage drop is only 1.5V at 20mA. Increasingly positive input voltage (above VFS) will produce increasing output current according to the transfer function, up to the output current limit of approximately 34mA. 12 1 V 3 (3) Bridge Sensor – 5 (2) RB + VR + IN V+LIN R LIN(3) 8 9 RLIN 10 V+ RG 4-20mA (1) RG R2 B XTR104 13 Q1 0.01µF R1 6 (3) – 4 V LIN 2 (1) RG = RG V–IN E IO IO = 4-20mA where VFS is Full Scale VIN. (2) RB ≥ 2750Ω. Otherwise add series resistance (see Figure 8). (3) See text — “Linearization”. FIGURE 1. Bridge Sensor Application, Connected for Positive Nonlinearity. ® 6 + + RL – VPS – 7 2500 Ω 1 –1 VFS XTR104 11 Possible choices for Q1 (see text). Type 2N4922 Package TO-225 TIP29B TO-220 TIP31B TO-220 With V+LIN and V–LIN connected to the bridge output, the bridge excitation voltage can be made to vary as much as ±0.5V in response to the bridge output voltage. Be sure that the total load on the VR output is less than 2mA at the maximum excitation voltage, VR = 5.5V. 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 XTR104. 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 VR output. The effective load of the trim circuit is nearly equal to R2. Total load on the VR output terminal must not exceed 2mA. An approximate value for R1 can be calculated: 5V • R B (3) R ≈ 1 4 • V TRIM Signal-dependent variation of the bridge excitation voltage provides a second-order term to the complete transfer function (including the bridge). This can be tailored to correct for bridge sensor nonlinearity. Either polarity of nonlinearity (bowing up or down) can be compensated by proper connection of the VLIN inputs. Connecting V+LIN to V+IN and V–LIN to V–IN (Figure 1) causes VR to increase with bridge output which compensates for a positive bow in the bridge response. Reversing the connections (Figure 3) causes VR to decrease with increasing bridge output, to compensate for negative-bowing nonlinearity. 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. To determine the required value for RLIN you must know the nonlinearity of the bridge sensor with constant excitation voltage. The linearization circuitry can only compensate for the parabolic portion of a sensor’s nonlinearity. Parabolic nonlinearity has a maximum deviation from linear occurring at mid-scale (see Figure 4). Sensors with nonlinearity curves similar to that shown in Figure 4, but not peaking exactly at mid-scale can be substantially improved. A nonlinearity that is perfectly “S-shaped” (equal positive and negative nonlinearity) cannot be corrected with the XTR104. It may, however, be possible to improve the worst-case nonlinearity of a sensor by equalizing the positive and negative nonlinearity. Figure 2 shows another way to adjust zero errors using the output current adjustment pins of the XTR104. This provides ±500µA (typical) adjustment around the initial lowscale output current. This is an output current adjustment that is independent of the input stage gain set with RG. If the input stage is set for high gain the output current adjustment may not provide sufficient range. (a) XTR104 The nonlinearity, B (in % of full scale), is positive or negative depending on the direction of the bow. A maximum of ±2.5% nonlinearity can be corrected. An approximate value for RLIN can be calculated by: 14 15 16 10kΩ ±500µA typical output current adjustment range. R (b) 14 15 5kΩ 5kΩ = K LIN • V FS (5) 0. 2 • B Where: KLIN ≈ 24000. VFS is the full-scale bridge output (in Volts) with constant 5V excitation. B is the parabolic nonlinearity in ±% of full scale. RLIN in Ω. XTR104 16 LIN ±50µA typical output current adjustment range. Methods for refining this calculation involve determining the actual value of KLIN for a particular device (explained later). FIGURE 2. Low-scale Output Current Adjustment. B is a signed number (negative for a downward-bowing nonlinearity). This can produce a negative value for RLIN. In this case, use the resistor value indicated (ignore the sign), but connect V+LIN to V–IN and V–LIN to V+IN as shown in Figure 3. LINEARIZATION Differential voltage applied to the linearization inputs, V+LIN and V–LIN, causes the reference (excitation) voltage, VR, to vary according to the following equation: (4) This approximate calculation of RLIN generally provides about a 5:1 improvement in bridge nonlinearity. Where: VLIN is the voltage applied to the V+LIN and V–LIN differential inputs (in V). RLIN in Ω. KLIN ≈ 24000 (approximately ±20% depending on variations in the fabrication of the XTR104). Example: The bridge sensor depicted by the negativebowing curve in Figure 4. Its full scale output is 10mV with constant 5V excitation. Its maximum nonlinearity, B, is –1.9% referred to full scale (occurring at mid-scale). Using equation 5: V = 5V + V R K LIN R LIN LIN ® 7 XTR104 12 1 (1) 3 Bridge Sensor 5 – + RB 9 RLIN V+LIN 10 V+ RG 4-20mA RG R2 R LIN 8 VR V+IN B XTR104 13 0.01µF R1 6 (1) RG E IO – 4 V LIN 2 11 + + RL – VPS – 7 V–IN IO = 4-20mA NOTE: (1) VLIN inputs connected for negative nonlinearity (B < 0). Pins 3 and 4 must be reversed for B > 0 (see Figure 1). FIGURE 3. Bridge Sensor, VLIN Connected for Negative Nonlinearity. R LIN ≈ 24000 • 0. 01 = −632 Ω 0. 2 • (−1. 9) BRIDGE TRANSDUCER TRANSFER FUNCTION WITH PARABOLIC NONLINEARITY Use RLIN = 632Ω. Because the calculation yields a negative result, connect V+LIN to V–IN and V–LIN to V+IN. 10 9 8 Bridge Output (mV) Gain is affected by the varying the excitation voltage. For each 1% of corrected nonlinearity, the gain must be altered by 4%. As a result, equation 2 will not provide an accurate RG when nonlinearity correction is used. The following equation calculates the required value for RG to compensate for this effect. 2500 RG = (6) 1 −1 (1 + 0. 04 • B) V Positive Nonlinearity B = +2.5% 7 6 5 4 B = –1.9% Negative Nonlinearity 3 2 Linear Response 1 0 FS 0 0.1 0.2 0.3 B must again be a signed number in this calculation— positive for positive bowing nonlinearity, and negative for a negative-bowing nonlinearity. K LIN = ∆V 1 Nonlinearity (% of Full Scale) Positive Nonlinearity B = +2.5% 1 0 –1 –2 Negative Nonlinearity B = –1.9% –3 (7) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Normalized Stimulus LIN Where: ∆VLIN is the change in voltage at VLIN. ∆VR is the measured change in reference voltage, VR. RTEST is a temporary fixed value of RLIN (in Ω). FIGURE 4. Parabolic Nonlinearity. ® XTR104 2 0 TEST 0.9 3 A more accurate value for RLIN can be determined by first measuring the actual gain constant of the linearization inputs, KLIN (see equation 4). Measure the change in the reference voltage, ∆VR, in response to a measured voltage change at the linearization inputs, ∆VLIN. Make this measurement with a known, temporary test value for RLIN. These measurements can be made during operation of the circuit by providing stimulus to the bridge sensor, or by temporarily unbalancing the bridge with a fixed resistor in parallel with one of the bridge resistors. Calculate the actual KLIN: R 0.8 NONLINEARITY vs STIMULUS RG = 23.32Ω for the example above. ∆V • R 0.4 0.5 0.6 0.7 Normalized Stimulus 8 0.8 0.9 1 OTHER SENSOR TYPES The XTR104 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 1V full scale. The linear common-mode range of the inputs is from 2V to 4V, referenced to the IO terminal, pin 7. Then, RLIN can be calculated using equation 5 using the accurate value of KLIN from equation 7. KLIN can be a different value for each XTR104. It is also possible to make a real-time adjustment of RLIN with a variable resistor (active circuit trimming). This is done by measuring the change in VR in response to a zeroto-VFS change in voltage applied to the VLIN inputs. To correct for each 1% of nonlinearity, the excitation voltage, VR, must make a 4% change at full-scale input. So the change in reference voltage, ∆VR, for a full-scale change in VLIN can be calculated by: ∆VR = 0.2 • B You can use the linearization feature of the XTR104 with any sensor whose output is ratiometric with an excitation voltage. For example, Figure 5 shows the XTR104 used with a potentiometer position sensor. (8) REVERSE-VOLTAGE PROTECTION Example: A bridge sensor has a –1.9% nonlinearity. Apply the full-scale bride output, VFS (10mV), to the VLIN inputs and adjust RLIN for: Figure 6 shows two ways to protect against reversed output connection lines. Trade-offs in an application will determine which technique is better. D1 offers series protection, but causes a 0.7V loss in loop supply voltage. This may be undesirable if V+ can approach the 9V limit. Using D2 (without D1) has no voltage loss, but high current will flow in the loop supply if the leads are reversed. This could damage the power supply or the sense resistor, RL. A diode with a higher current rating is needed for D2 to withstand the highest current that could occur with reversed lines. VR'’ = 5V + 0.2 • B = 4.62V Note that with all the calculation and adjustment methods described above, the full-scale bridge output is no longer equal to VFS because the excitation voltage at full scale is no longer 5V. All the calculations and adjustment procedures described above assume VFS to be the full-scale bridge output with constant 5V excitation. It is not necessary to iterate the calculations or adjustment procedures using the new full-scale bridge output as a starting point. However, a new value for RG must be calculated using equation 6. SURGE PROTECTION Long lines may be subject to voltage surges which can damage semiconductor components. To avoid damage, the maximum applied voltage rating for the XTR104 is 40V. A zener diode can be used for D2 (Figure 7) to clamp the voltage applied to the XTR104 to a safe level. The loop power supply voltage must be lower than the voltage rating of the zener diode. A refined value for RLIN, arrived at either by active circuit trimming, or by measuring linearization gain (equation 7) will improve linearity. Reduction of the original parabolic nonlinearity of the sensor can approach 40:1. Actual results will depend on higher-order nonlinearity of the sensor. There are special zener diode types (Figure 7) specifically designed to provide a very low impedance clamp and withstand large energy surges. These devices normally have a diode characteristic in the forward direction which also If no linearity correction is desired, make no connections to the RLIN pins (RLIN = ∞). This will cause the VR output to remain a constant +5V. The V+LIN and V–LIN inputs should remain connected to the bridge output to keep these inputs biased in their active region. 5V 12 1 8kΩ 3 2.5V to 3V 5 VR V+IN 8 RLIN 9 V+LIN RLIN 10 V+ RG 2.5kΩ RG 4-20 mA B XTR104 13 2kΩ 6 10kΩ 4 10kΩ 2.5V 2 E RG V–LIN V–IN IO 11 0.01µF + + RL – VPS – 7 10kΩ FIGURE 5. Potentiometer Sensor Application. ® 9 XTR104 protects against reversed loop connections. As noted earlier, reversed loop connections would produce a large loop current, possibly damaging RL. Bypass capacitors on the input often reduce or eliminate this interference. Connect these bypass capacitors to the IO terminal (see Figure 7). Although the DC voltage at the IO terminal is not equal to 0V (at the loop supply, VPS) this circuit point can be considered the transmitter’s “ground”. 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 XTR104 causing errors. This generally appears as an unstable output current that varies with the position of loop supply or input wiring. LOW-IMPEDANCE BRIDGES Low impedance bridges can be used with the XTR104 by adding series resistance to limit excitation current to ≤2mA. Equal resistance should be added to the upper and lower sides of the of the bridge (Figure 8) to keep the bridge output voltage centered at approximately 2.5V. Bridge output is reduced, so a preamplifier, as shown, may be needed to reduce offset and drift. If the bridge sensor is remotely located from the XTR104, 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. 1N4148 D1 Use either D1 or D2. See “Reverse Voltage Protection.” 10 V+ XTR104 B E 0.01µF 13 D2 1N4001 VPS RL 11 IO 7 FIGURE 6. Reverse Voltage Protection. Zener diode 36V: 1N4753A or General Semiconductor Transorb™ 1N6286A, special low impedence clamp type. Use lower voltage zener diodes with loop power supply voltages less than 30V for increased protection. 12 1 3 Bridge Sensor – 5 RB VR V+IN V+LIN B RG – 4 V LIN 2 V–IN E 13 11 Q1 0.01µF IO D2 + + RL – VPS – 7 IO = 4-20mA 0.01µF FIGURE 7. Over-Voltage Surge Protection. ® XTR104 10 V+ 4-20mA XTR104 6 0.01µF 9 RLIN RG RG + R LIN 8 10 Maximum VPS must be less than minimum voltage rating of zener diode. 1.37mA at 5V ≈ 400µA 1.65kΩ RLIN + 1kΩ 1 V+ IN LT1049 8 VR 9 10 + 3 V LIN V+ R 5 G RG 13 B XTR104 25Ω 6 E R IO 11 4 –G V LIN 7 V–IN 2 – 90kΩ 1µF 350Ω 1N4148 12 9.4kΩ 0.01µF IO = 4-20mA 1.65kΩ Bridge Excitation Voltage = 0.42V approx. x10 Amplifier FIGURE 8. 350Ω Bridge With X10 Preamplifier. +12V 1 Bridge Sensor 3 5 – RB RG + 12 V+IN V+LIN RLIN 8 9 10 VR B 13 0.01µF 16 E 10 3 IO 11 11 12 7 – V 1µF V+ RG XTR104 6 R 4 –G V LIN 2 1N4148 VO = 0 to 5V 15 IN RCV420 2 IO = 4-20mA 14 13 5 4 1µF –12V FIGURE 9. ±12V-Powered Transmitter/Receiver Loop. 1 Bridge Sensor 3 5 – RB + 12 V+IN V+LIN 8 VR RG XTR104 RG 6 R 4 –G V LIN 2 V – RLIN 1N4148 +15V 1µF 9 10 0 V+ B 1µF 13 –15V 0.01µF E IO 11 16 10 3 11 12 7 RCV420 2 14 13 4 V+ 1 15 IN IO = 4-20mA Isolated Power from PWS740 9 15 ISO122 5 10 7 8 VO 0 – 5V 2 16 V– FIGURE 10. Isolated Transmitter/Receiver Loop. ® 11 XTR104 PACKAGE OPTION ADDENDUM www.ti.com 9-Dec-2004 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Drawing Pins Package Eco Plan (2) Qty Lead/Ball Finish MSL Peak Temp (3) XTR104AP OBSOLETE PDIP N 16 None Call TI Call TI XTR104AU OBSOLETE SOIC DW 16 None Call TI Call TI XTR104AU/1K OBSOLETE SOIC DW 16 None Call TI Call TI XTR104BP OBSOLETE PDIP N 16 None Call TI Call TI XTR104BU OBSOLETE SOIC DW 16 None Call TI Call TI (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 - May not be currently available - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. None: Not yet available Lead (Pb-Free). 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. Green (RoHS & no Sb/Br): TI defines "Green" to mean "Pb-Free" and in addition, uses package materials that do not contain halogens, including bromine (Br) or antimony (Sb) above 0.1% of total product weight. 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