RCV420

® RCV 420 RCV420 Precision 4mA to 20mA CURRENT LOOP RECEIVER FEATURES q COMPLETE 4-20mA TO 0-5V CONVERSION q INTERNAL SENSE RESISTORS q PRECISION 10V REFERENCE q BUILT-IN LEVEL-SHIFTING q ±40V COMMON-MODE INPUT RANGE q 0.1% OVERALL CONVERSION ACCURACY q HIGH NOISE IMMUNITY: 86dB CMR APPLICATIONS q PROCESS CONTROL q INDUSTRIAL CONTROL q FACTORY AUTOMATION q DATA ACQUISITION q SCADA q RTUs q ESD q MACHINE MONITORING DESCRIPTION The RCV420 is a precision current-loop receiver designed to convert a 4–20mA input signal into a 0–5V output signal. As a monolithic circuit, it offers high reliability at low cost. The circuit consists of a premium grade operational amplifier, an on-chip precision resistor network, and a precision 10V reference. The RCV420 features 0.1% overall conversion accuracy, 86dB CMR, and ±40V common-mode input range. The circuit introduces only a 1.5V drop at full scale, which is useful in loops containing extra instrument burdens or in intrinsically safe applications where V+ 16 RCV420 300kΩ –In 1 RS 75Ω CT 2 RS 75Ω +In 3 300kΩ 100kΩ 13 Rcv Com 5 Ref Com 1.01kΩ +10V Ref 99kΩ V– 4 transmitter compliance voltage is at a premium. The 10V reference provides a precise 10V output with a typical drift of 5ppm/°C. The RCV420 is completely self-contained and offers a highly versatile function. No adjustments are needed for gain, offset, or CMR. This provides three important advantages over discrete, board-level designs: 1) lower initial design cost, 2) lower manufacturing cost, and 3) easy, cost-effective field repair of a precision circuit. Ref In 12 92kΩ 11.5kΩ 15 Rcv fB 14 Rcv Out 11 Ref Out 10 Ref fB 8 7 Ref Trim Ref Noise Reduction 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 Internet: http://www.burr-brown.com/ • FAXLine: (800) 548-6133 (US/Canada Only) • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132 ® © 1988 Burr-Brown Corporation PDS-837E 1 Printed in U.S.A. October, 1997 RCV420 SPECIFICATIONS ELECTRICAL At T = +25° C and VS = ±15V, unless otherwise noted. RCV420KP, JP CHARACTERISTICS GAIN Initial Error Error—JP Grade vs Temp Nonlinearity(1) OUTPUT Rated Voltage (IO = +10mA, –5mA) Rated Current (EO = 10V) Impedance (Differential) Current Limit (To Common) Capacitive Load (Stable Operation) INPUT Sense Resistance Input Impedance (Common-Mode) Common-Mode Voltage CMR(2) vs Temp (DC) (TA = TMIN to TMAX) AC 60Hz OFFSET VOLTAGE (RTO)(3) Initial vs Temp vs Supply (±11.4V to ±18V) vs Time ZERO ERROR(4) Initial Initial—JP Grade vs Temp OUTPUT NOISE VOLTAGE fB = 0.1Hz to 10Hz fO = 10kHz DYNAMIC RESPONSE Gain Bandwidth Full Power Bandwidth Slew Rate Settling Time (0.01%) VOLTAGE REFERENCE Initial Trim Range(5) vs Temp vs Supply (±11.4V to ±18V) vs Output Current (IO = 0 to +10mA) vs Time Noise (0.1Hz to 10Hz) Output Current POWER SUPPLY Rated Voltage Range(6) Quiescent Current (VO = 0V) TEMPERATURE RANGE Specification Operation Storage Thermal Resistance, θJA 9.99 ±4 5 0.0002 0.0002 15 5 +10, –2 ±15 –5, +11.4 3 0 –25 –40 80 10 +10, –5 MIN TYP 0.3125 0.05 15 0.0002 12 0.01 +49, –13 1000 MAX UNITS V/mA % of span % of span ppm/°C % of span V mA Ω mA pF 0.15 0.25 0.002 74.25 75 200 80 76 80 75.75 ±40 70 Ω kΩ V dB dB dB mV µV/°C dB µV/mo % of span % of span ppm of span/° C µVp-p nV/√Hz kHz kHz V/µs µs 1 74 10 90 200 0.025 10 0.075 0.15 50 800 150 30 1.5 10 10.01 V % ppm/°C %/V %/mA ppm/kHz µVp-p mA V V mA °C °C °C °C/W ±18 4 +70 +85 +85 NOTES: (1) Nonlinearity is the max peak deviation from best fit straight line. (2) With 0 source impedance on Rcv Com pin. (3) Referred to output with all inputs grounded including Ref In. (4) With 4mA input signal and Voltage Reference connected (includes VOS, Gain Error, and Voltage Reference Errors). (5) External trim slightly affects drift. (6) IO Ref = 5mA, IO Rcv = 2mA. ® RCV420 2 PIN CONFIGURATION Top View DIP ABSOLUTE MAXIMUM RATINGS(1) Supply ............................................................................................... ±22V Input Current, Continuous ................................................................ 40mA Input Current Momentary, 0.1s ........................... 250mA, 1% Duty Cycle Common-Mode Input Voltage, Continuous ....................................... ±40V Lead Temperature (soldering, 10s) ............................................... +300°C Output Short Circuit to Common (Rcv and Ref) ..................... Continuous NOTE: (1) Stresses above these ratings may cause permanent damage. –In CT +In V– Ref Com NC Ref Noise Reduction Ref Trim 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 V+ Rcv fB Rcv Out Rcv Com Ref In Ref Out Ref fB NC PACKAGE INFORMATION PRODUCT RCV420KP RCV420JP PACKAGE 16-Pin Plastic DIP 16-Pin Plastic DIP PACKAGE DRAWING NUMBER(1) 180 180 NOTE: (1) For detailed drawing and dimension table, please see end of data sheet, or Appendix C of Burr-Brown IC Data Book. ORDERING INFORMATION PERFORMANCE GRADE 0°C to +70°C 0°C to +70°C PRODUCT RCV420KP RCV420JP PACKAGE 16-Pin Plastic DIP 16-Pin Plastic DIP 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 RCV420 TYPICAL PERFORMANCE CURVES At TA = +25°C, VS = ±15V, unless otherwise noted. STEP RESPONSE NO LOAD SMALL SIGNAL RESPONSE NO LOAD SMALL SIGNAL RESPONSE RL = ∞, CL = 1000pF POSITIVE COMMON-MODE VOLTAGE RANGE vs POSITIVE POWER SUPPLY VOLTAGE 80 TA = –55°C 70 TA = +25°C 60 TA = +125°C Max Rating = 40V 40 –VS = –5V to –20V 30 11 11.4 12 13 14 15 16 17 18 19 20 Positive Power Supply Voltage (V) –80 NEGATIVE COMMON-MODE VOLTAGE RANGE vs NEGATIVE POWER SUPPLY VOLTAGE Negative Common-Mode Range (V) Positive Common-Mode Range (V) –70 TA = +25°C –60 –50 –40 –30 +VS = +11.4V to +20V –20 –10 –5 –10 –15 –20 Negative Power Supply Voltage (V) Max Rating = –40V TA = –55°C to +125°C 50 COMMON-MODE REJECTION vs FREQUENCY 100 100 90 80 80 POWER-SUPPLY REJECTION vs FREQUENCY CMR (dB) PSR (dB) V+ 60 V– 60 40 1 10 100 1k 10k 100k Frequency (Hz) 40 1 10 100 1k 10k 100k Frequency (Hz) ® RCV420 4 THEORY OF OPERATION Refer to the figure on the first page. For 0 to 5V output with 4–20mA input, the required transimpedance of the circuit is: VOUT /IIN = 5V/16mA = 0.3125V/mA. To achieve the desired output (0V for 4mA and 5V for 20mA), the output of the amplifier must be offset by an amount: VOS = – (4mA)(0.3125V/mA) = –1.25V. The input current signal is connected to either +In or –In, depending on the polarity of the signal, and returned to ground through the center tap, CT. The balanced input—two matched 75Ω sense resistors, RS—provides maximum rejection of common-mode voltage signals on CT and true differential current-to-voltage conversion. The sense resistors convert the input current signal into a proportional voltage, which is amplified by the differential amplifier. The voltage gain of the amplifier is: AD = 5V/(16mA)(75Ω) = 4.1667V/V. The tee network in the feedback path of the amplifier provides a summing junction used to generate the required –1.25V offset voltage. The input resistor network provides high-input impedance and attenuates common-mode input voltages to levels suitable for the operational amplifier’s common-mode signal capabilities. BASIC POWER SUPPLY AND SIGNAL CONNECTIONS Figure 1 shows the proper connections for power supply and signal. Both supplies should be decoupled with 1µF tantalum capacitors as close to the amplifier as possible. To avoid gain and CMR errors introduced by the external circuit, connect grounds as indicated, being sure to minimize ground resistance. The input signal should be connected to either +In or –In, depending on its polarity, and returned to ground through the center tap, CT. The output of the voltage reference, Ref Out, should be connected to Ref In for the necessary level shifting. If the Ref In pin is not used for level shifting, then it must be grounded to maintain high CMR. GAIN AND OFFSET ADJUSTMENT Figure 2 shows the circuit for adjusting the RCV420 gain. Increasing the gain of the RCV420 is accomplished by inserting a small resistor in the feedback path of the amplifier. Increasing the gain using this technique results in CMR degradation, and therefore, gain adjustments should be kept as small as possible. For example, a 1% increase in gain is typically realized with a 125Ω resistor, which degrades CMR by about 6dB. A decrease in gain can be achieved by placing matched resistors in parallel with the sense resistors, also shown in Figure 2. The adjusted gain is given by the following expression VOUT/IIN = 0.3125 x RX /(RX + RS). A 1% decrease in gain can be achieved with a 7.5kΩ resistor. It is important to match the parallel resistance on each sense resistor to maintain high CMR. The TCR mismatch between the two external resistors will effect gain error drift and CMR drift. There are two methods for nulling the RCV420 output offset voltage. The first method applies to applications using the internal 10V reference for level shifting. For these applica- –In CT +In 10kΩ(1) 10kΩ(1) RX RX 1 2 3 15 R1 200Ω(1) 14 ±0.5% Gain Adjustment RCV420 Rcv Out NOTE: (1) Typical values. See text. FIGURE 2. Optional Gain Adjustment. IIN 4–20mA 12 +In CT 3 15 2 RS RS –In 1 +10V Reference 75 Ω RCV420 75 Ω 14 11 10 8 7 Ref In Rcv fB Rcv Out Ref Out Ref fB Ref Trim Ref Noise Reduction VO (0–5V) V+ 1µF 16 1µF 4 V– 13 Rcv Com 5 Ref Com FIGURE 1. Basic Power Supply and Signal Connections. ® 5 RCV420 tions, the voltage reference output trim procedure can be used to null offset errors at the output of the RCV420. The voltage reference trim circuit is discussed under “Voltage Reference.” When the voltage reference is not used for level shifting or when large offset adjustments are required, the circuit in Figure 3 can be used for offset adjustment. A low impedance on the Rcv Com pin is required to maintain high CMR. ZERO ADJUSTMENT Level shifting the RCV420 output voltage can be achieved using either the Ref In pin or the Rcv Com pin. The disadvantage of using the Ref In pin is that there is an 8:1 voltage attenuation from this pin to the output of the RCV420. Thus, use the Rcv Com pin for large offsets, because the voltage on this pin is seen directly at the output. Figure 4 shows the circuit used to level-shift the output of the RCV420 using the Rcv Com pin. It is important to use a low-output impedance amplifier to maintain high CMR. With this method of zero adjustment, the Ref In pin must be connected to the Rcv Com pin. MAINTAINING COMMON-MODE REJECTION Two factors are important in maintaining high CMR: (1) resistor matching and tracking (the internal resistor network does this) and (2) source impedance. CMR depends on the accurate matching of several resistor ratios. The high accuracies needed to maintain the specified CMR and CMR temperature coefficient are difficult and expensive to reliably achieve with discrete components. Any resistance imbalance introduced by external circuitry directly affects CMR. These imbalances can occur by: mismatching sense resistors when gain is decreased, adding resistance in the feedback path when gain is increased, and adding series resistance on the Rcv Com pin. The two sense resistors are laser-trimmed to typically match within 0.01%; therefore, when adding parallel resistance to decrease gain, take care to match the parallel resistance on each sense resistor. To maintain high CMR when increasing the gain of the RCV420, keep the series resistance added to the feedback network as small as possible. Whether the Rcv Com pin is grounded or connected to a voltage reference for level shifting, keep the series resistance on this pin as low as possible. For example, a resistance of 20Ω on this pin degrades CMR from 86dB to approximately 80dB. For applications requiring better than 86dB CMR, the circuit shown in Figure 5 can be used to adjust CMR. PROTECTING THE SENSE RESISTOR The 75Ω sense resistors are designed for a maximum continuous current of 40mA, but can withstand as much as 250mA for up to 0.1s (see absolute maximum ratings). There are several ways to protect the sense resistor from –In CT +In 1 15 2 3 13 +15V 12 OPA237 ±150mV adjustment at output. 1k Ω –15V 100k Ω 100k Ω RCV420 5 14 VO FIGURE 3. Optional Output Offset Nulling Using External Amplifier. –In CT +In Use 10V Ref for + and 10V Ref with INA105 for –. 1 15 2 3 5 13 12 V ZERO OPA237 10k Ω 50kΩ 10k Ω +10V 3 RCV420 10 14 11 2 5 INA105 1 6 –10V OPA237 1kΩ 1kΩ 200Ω CMR Adjust VO = (0.3125)(I IN ) + V ZERO VO RCV420 13 1kΩ 1kΩ Procedure: 1. Connect CMV to C T. 2. Adjust potentiometer for near zero at the output. ±5V adjustment at output. FIGURE 4. Optional Zero Adjust Circuit. FIGURE 5. Optional Circuit for Externally Trimming CMR. ® RCV420 6 overcurrent conditions exceeding these specifications. Refer to Figure 6. The simplest and least expensive method is a resistor as shown in Figure 6a. The value of the resistor is determined from the expression RX = VCC /40mA – 75Ω and the full scale voltage drop is VRX = 20mA x RX. For a system operating off of a 32V supply RX = 725Ω and VRX = 14.5V. In applications that cannot tolerate such a large voltage drop, use circuits 6b or 6c. In circuit 6b a power JFET and source resistor are used as a current limit. The 200Ω potentiometer, RX, is adjusted to provide a current limit of approximately 30mA. This circuit introduces a 1–4V drop at full scale. If only a very small series voltage drop at full scale can be tolerated, then a 0.032A series 217 fast-acting fuse should be used, as shown in Figure 6c. For automatic fold-back protection, use the circuit shown in Figure 15. VOLTAGE REFERENCE The RCV420 contains a precision 10V reference. Figure 8 shows the circuit for output voltage adjustment. Trimming the output will change the voltage drift by approximately 0.007ppm/°C per mV of trimmed voltage. Any mismatch in TCR between the two sides of the potentiometer will also affect drift, but the effect is divided by approximately 5. The trim range of the voltage reference using this method is typically ±400mV. The voltage reference trim can be used to trim offset errors at the output of the RCV420. There is an 8:1 voltage attenuation from Ref In to Rcv Out, and thus the trim range at the output of the receiver is typically ±50mV. The high-frequency noise (to 1MHz) of the voltage reference is typically 1mVp-p. When the voltage reference is used for level shifting, its noise contribution at the output of the receiver is typically 125µVp-p due to the 8:1 attenuation from Ref In to Rcv Out. The reference noise can be reduced by connecting an external capacitor between the Noise Reduction pin and ground. For example, 0.1µF capacitor reduces the high-frequency noise to about 200µVp-p at the output of the reference and about 25µVp-p at the output of the receiver. V+ VRX RX 4–20mA 3 2 1 RCV420 15 14 VO a) RX = (V+)/40mA – 75Ω V+ 2N3970 200 Ω 4–20mA 3 2 1 RCV420 15 14 VO RX b) RX set for 30mA current limit at 25°C. V+ f1 4–20mA 3 2 1 RCV420 15 14 VO c) f1 is 0.032A, Lifflefuse Series 217 fast-acting fuse. Request Application Bulletin AB-014 for details of a more complete protection circuit. FIGURE 6. Protecting the Sense Resistors. –In CT +In 1 15 2 3 10 8 20kΩ V REF RCV420 11 14 VO ±400mV adjustment at output of reference, and ±50mV adjustment at output of receiver if reference is used for level shifting. FIGURE 7. Optional Voltage Reference External Trim Circuit. ® 7 RCV420 12 13 VLIN + VIN 1 IR1 1N4148 14 IR2 11 10 V+ 1µF B9 +12V VREG 4 RLIN1 5760Ω RG 402Ω 3 RG XTR105 RG – VIN Q1 0.01µF 3 16 10 E8 IO 11 12 15 VO = 0 to 5V 14 13 RCV420 7 IO = 4mA – 20mA 2 4 5 2 Pt100 100°C to 600°C IRET RTD RZ 137Ω 6 1µF –12V RCM = 1kΩ NOTE: A two-wire RTD connection is shown. For remotely located RTDs, a three-wire RTD conection is recommended. RG becomes 383Ω, RLIN2 is 8060Ω. See Figure 3 and Table I. 0.01µF FIGURE 8. RCV420 Used in Conjunction with XTR101 to Form a Complete Solution for 4-20mA Loop. 12 RLIN1 RLIN2 13 VLIN + VIN 1 IR1 1N4148 14 11 IR2 10 VREG V+ +15V 1µF 0 1µF Isolated Power from PWS740 4 RG XTR105 B E RG IO – RG 3 9 8 Q1 0.01µF 3 –15V 16 10 11 12 15 1 15 ISO122 10 2 16 V– 9 7 8 VO 0 – 5V V+ 14 13 RCV420 7 IO = 4mA – 20mA 2 4 5 RZ 2 VIN IRET 6 RTD NOTE: A three-wire RTD connection is shown. For a two-wire RTD connection eliminate RLIN2. RCM = 1kΩ 0.01µF FIGURE 9. Isolated 4-20mA Instrument Loop (RTD shown). ® RCV420 8 10 4–20mA +In CT –In 3 2 1 RS RS RCV420 (1) 13 5 11 12 15 14 VO (0–5V) 3 15 2 1 5 4–20mA 12 13 12k Ω +6.25V +6.25V OPA237 CT RCV420 10 +10V 14 11 VO (5–0V) 10 +In CT –In RCM(1) 3 2 1 RS RS RCV420 (N) 13 5 IL NOTE: (1) RCM and RG are used to provide a first order correction of CMR and Gain Error, respectively. Table 1 gives typical resistor values for RCM and RG when as many as three RCV420s are stacked. Table II gives typical CMR and Gain Error with no correction. Further improvement in CMR and Gain Error can be achieved using a 500kΩ potentiometer for RCM and a 100Ω potentiometer for RG. Load +In RX(1) 3 RS 2 RX(1) 1 RS 12 5 11 12 15 14 VO (0–5V) VO = 6.25V – (0.3125) (IIN) RG(1) 20k Ω FIGURE 12. 4-20mA to 5-0V Conversion. 15 RCV420 13 14 VO (0-5V) CT RCV420 1 2 3 RCM (kΩ) RG (Ω) 0 7 23 Power Supply +In ∞ 200 67 –40V (max) TABLE 1. Typical Values for RCM and RG. RCV420 1 2 3 CMR (dB) 94 68 62 GAIN ERROR % 0.025 0.075 0.200 +40V (max) Power Supply +In RX(1) RS RCV420 RS 12 Load IL NOTE: (1) RX = RS/ 5 13 15 14 VO (0-5V) CT RX (1) TABLE II. Typical CMR and Gain Error Without Correction. FIGURE 10. Series 4-20mA Receivers. –In I1 (16mA –1 ) IL MAX +In CT 3 2 1 RS RCV420 RS 12 5 13 15 14 VO FIGURE 13. Power Supply Current Monitor Circuit. I2 –In VO = 0.3125 (I1 – I2) Max Gain Error = 0.1% (RCV420BG) FIGURE 11. Differential Current-to-Voltage Converter. ® 9 RCV420 +15V 16 –15V 4 300kΩ RCV420 99kΩ 92kΩ 1 12 15 VOUT 0–5V 10.0V 10 75Ω 2 75Ω 3 300kΩ +5V 100kΩ 13 5 1.01kΩ 11.5kΩ 14 10.0V Reference 11 1.27kΩ +15V 8 1MΩ 7 AT&T LH1191 Solid-State Relay 6 1µF 3 1 555 Timer 8 4 2 5 0.01µF LM193 10kΩ 10kΩ 10kΩ 10kΩ 10kΩ 6.95V 4–20mA Input 470Ω 47kΩ 4 0.57V 604Ω 22.9kΩ 1µF Overrange Output 2N3904 Underrange Output See Application Bulletin AB-014 for more details. FIGURE 14. 4-20mA Current Loop Receiver with Input Overload Protection. +15V 16 1 301Ω 0-20mA Input 301Ω 3 300kΩ 2 300kΩ 75Ω –15V 4 RCV420 99kΩ 92kΩ 15 11.5kΩ 14 10 10.0V Ref 11 13 5 VO 0-5V 12 75Ω 1.01kΩ 100kΩ See Application Bulletin AB-018 for more details. FIGURE 15. 0-20mA/0-5V Receiver Using RCV420. ® RCV420 10