VOLTAGE/CURRENT CONVERTER AM422 FEATURES GENERAL DESCRIPTION • Wide Supply Voltage Range: 6...35V • Wide Operating Temperature Range: –40°C...+85°C • Adjustable Voltage Reference: 4.5 to 10V • Operational Amplifier Input: 0.5...4.5V, 0...5V, other • Adjustable Offset Current • Available as Three– (0/4...20mA) or Two–Wire Version (4...20mA) • Adjustable Output Current Range • Protection Against Reverse Polarity • Protected Current Output The AM422 is a low cost monolithic voltage– to–current converter specially designed for analog signal transmission. The AM422 is available in a 3– or 2–wire version, which allows applications with flexible input voltage ranges to be used for a standard output current. Output current range and current offset level are freely adjustable by external resistors. The IC consists of three basic sections: an operational amplifier input stage for single ended input signals (0.5–4.5V, 0–10V, or other), a programmable 4.5 to 10V reference for transducer excitation, and a current output, freely adjustable in a wide current range (4–20mA, 0–20mA, other). With the broad spectrum of possible input signals the AM422 is a flexible and multipurpose voltage–to–current converter for single ended transducers or voltage transmission. APPLICATIONS • • • • Sensor Interface Industrial Process Control Programmable Current Source Current Source Reference DELIVERY • DIL8 packages (samples) • SOP8 packages • Dice on 5“ blue foil BLOCK DIAGRAM VSET VREF 6 SET 8 AM422 1 5 VREF 2 Reference Voltage G=1 V VIN 4 2 VCC RS Input Amplifier I 3 OUT 7 GND Figure 1 analog microelectronics Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz Internet: www.analogmicro.de Phone: +49 (0)6131/91 073 – 0 Fax: +49 (0)6131/91 073 – 30 E–Mail: [email protected] April 99 1/10 Rev. 2.1 VOLTAGE/CURRENT CONVERTER AM422 ELECTRICAL SPECIFICATIONS Tamb = 25°C, VCC = 24V, VREF = 5V, IREF = 1mA (unless otherwise noted) Parameter Symbol Voltage Range VCC Quiescent Current ICC Conditions Min. Typ. 6 Tamb = – 40...+85°C, IREF = 0mA Max. Unit 35 V 1.5 mA 85 °C Temperature Specifications Operating Tamb –40 Storage Tst –55 Junction TJ Thermal Resistance Θja DIL8 plastic package 110 °C/W Θja SO8 plastic package 180 °C/W VREF VSET not connected 4.75 5.00 5.25 VREF VSET = GND, VCC ≥ 11V 9.5 10.0 125 °C 150 °C Voltage Reference Voltage V 10.5 V Trim Range VR10 4.5 VR10 V Current IREF* 0 10 mA ±90 ±140 ppm/°C 30 80 ppm/V VREF vs. Temperature dVREF/dT Tamb = – 40...+85°C Line Regulation dVREF/dV VCC = 6V...35V dVREF/dV VCC = 6V...35V, IREF ≈ 5mA Load Regulation dVREF/dI dVREF/dI Load Capacitance IREF ≈ 5mA CL 1.9 60 150 ppm/V 0.05 0.10 %/mA 0.06 0.15 %/mA 2.2 5.0 µF ±3 mV Set Stage Internal Gain GIA 1 Input Voltage VSET Offset Voltage VOS ±1 VOS vs. Temperature dVOS/dT ±5 Input Bias Current IB 8 20 nA IB vs. Temperature dIB/dT 6 15 pA/°C 2.6 ISET = 4mA, R0 = 25Ω V µV/°C Input Stage Internal Gain GIN Input Voltage VIN 1.15 V Offset Voltage VOS ±0.5 ±2.5 mV VOS vs. Temperature dVOS/dT ±1.6 ±5 µV/°C Input Bias Current IB 8 20 nA IB vs. Temperature dIB/dT 7 18 pA/°C analog microelectronics 0.5 0 April 99 2/10 VOLTAGE/CURRENT CONVERTER Parameter Symbol Conditions Min. AM422 Typ. Max. Unit V/I Converter Internal Gain GVI 1.00 Trim Range adjustable by R0 0.75 1.00 1.25 400 Voltage Range at R0 FS VR0FS 500 580 mV Offset Voltage VOS β F ≥ 100 ±2 ±6 mV VOS vs. Temperature dVOS/dT β F ≥ 100 ±7 ±20 µV/°C Output Offset Current IOUTOS 3–wire operation –35 –50 µA IOUTOS vs. Temperature dIOUTOS/dT 3–wire operation 55 80 nA/°C Output Offset Current IOUTOS 2–wire operation 14 22 µA IOUTOS vs. Temperature dIOUTOS/dT 2–wire operation 22 35 nA/°C Output Control Current IOUTC 2–wire operation, VR0/100mV 5 IOUTC vs. Temperature dIOUTC/dT 2–wire operation Output Voltage Range VOUT VOUT = RL IOUT, VCC < 16V 0 0 VOUT VOUT = RL IOUT, VCC ≥ 16V Output Current Range FS IOUTFS IOUT = VR0/R0, 3–wire operation Output Resistance ROUT Load Capacitance CL µA –9 nA/°C VCC – 6 10 20 0.5 V mA 1.0 0 V MΩ 500 nF 690 mV Protection Functions Voltage Limitation at R0 Temperature Limitation VLIMR0 VR0 = VIN/2, SET = VREF/2 VLIMR0 VIN = 0, VR0 = VSET/2 – VREF/2 TLIMIT 580 635 580 640 700 mV 110 130 150 °C 35 V Protection against reverse polarity Ground vs. VS vs. IOUT Current in case of reverse polarity Ground = 35V, VS = IOUT = 0 3.8 ideal input 0.05 0.15 %FS Typ. Max. Unit mA System Parameters Nonlinearity * In 2–wire operation a maximum current of IOUTmin – ICC is valid Currents flowing into the IC are negative BOUNDARY CONDITIONS Parameter Sense Resistor Stabilisation Resistor Load Resistance Sum Offset Resistors Symbol Conditions R0 IOUTFS = 20mA R0 c = 20mA/IOUTFS R5 IOUTFS = 20mA R5 c = 20mA/IOUTFS RL limitation only for 3–wire operation R3 + R4 Min. 20 25 29 Ω c ⋅ 20 c ⋅ 25 c ⋅ 29 Ω 35 40 45 Ω c ⋅ 35 c ⋅ 40 c ⋅ 45 Ω 0 500 Ω 20 200 kΩ 1.9 2.2 5.0 µF 90 100 250 nF VREF Capacitance C1 Output Capacitance C2 D1 Breakdown Voltage VBR 35 50 T1 Forward Current Gain βF 50 150 only for 2–wire operation analog microelectronics V April 99 3/10 VOLTAGE/CURRENT CONVERTER AM422 FUNCTIONAL DIAGRAMS Voltage Reference 3−Wire System VS RA Input Amplifier V IOUT VIN RIN I RL Ground Figure 2 Voltage Reference 2−Wire System VS RA Input Amplifier VIN RIN V IOUT I RL Ground Figure 3 FUNCTIONAL DESCRIPTION The IC AM422 is an integrated voltage–to–current converter for a broad spectrum of possible single ended input signals. With variations of a few external components the output current can be adjusted over a wide range. In addition to the resistors R0 – R5 and the capacitor C1 (C2), the circuitry needs only an output transistor T1 and a diode D1. The external transistor decreases the power dissipation of the IC and the diode is protecting the transistor against reverse polarity. Typical values for the external components are listed in the Application Notes. In principle the AM422 can be used as a two–wire or as a three–wire voltage–to–current interface. The schematic of the entire system for the three–wire output is demonstrated on Figure 2. The external reference point Ground has to be identical to the ground pin 7 (GND) and the IC supply voltage becomes VCC = VS. Opposed to this, the ground pin 7 in the two–wire mode (Figure 3) (GND) analog microelectronics April 99 4/10 VOLTAGE/CURRENT CONVERTER AM422 has to be connected between the resistors R5 and RL. In this case the IC supply voltage VCC depends on the voltage VS and the load resistor RL and can be calculated: VCC = VS − IOUT ⋅ RL (1) Basically the IC AM422 is composed of 3 functional sections as they shown in Figure 1: 1. An operational amplifier input which allows the adjustment of the output current range with the two external resistors R1 and R2. With the variation of the resistors the input voltage range and the output current range can be set. 2. A voltage controlled current output, with a wide current range is adjustable with external resistors RSET, R3 and R4. The resistors fix the output offset current, which depends on the reference voltage and corresponds to a minimal output current. The output current IOUT is supplied by the external transistor T1, driven by the output of the IC pin 3 (OUT). 3. A programmable voltage reference (VSET = N.C. or VSET = GND) can be used as an excitation for constant voltage sensors or as supply for other external devices. The output current is based on two partial currents: an adjustable offset current and a current relying on the input signal VIN. The transfer function of the AM422 is then I OUT (VSET ,VIN ) = I SET (VSET ) + I IN (VIN ) (2) For the adjustment of the AM422 two cases have to be differentiated. For input voltage ranges without an offset voltage (0...5V, 0...10V) the adjustment of the output current range is as follows: The minimum output current has to be set with an input voltage VIN = 0V. The output offset current becomes I SET (VIN = 0) = V V ( R + RSET ) − R3 1 ⋅ VSET − REF = REF ⋅ 4 R0 2 R0 2 ( R3 + R4 + RSET ) (3) With R3 = R4 and simplifications the set resistor RSET is RSET ≈ 4 R0 R4 I SET VREF (4) The output current range has to be set with the transfer function of the IC and can be calculated by ∆I OUT = I OUTmax − I SET = VINmax R2 2 R0 R1 + R2 (5) The relationship of R1/R2 becomes R1 VINmax = −1 R2 2 R0 ( I OUTmax − I SET ) (6) The adjustment of the IC using an input offset voltage (for example 0.5...4.5V) can be described as follows. For a desired change of the output current of ∆IOUT ∆I OUT = ∆V PIN 4 2 R0 ⇒ analog microelectronics ∆V PIN 4 = 2 R0 ∆I OUT (7) April 99 5/10 VOLTAGE/CURRENT CONVERTER AM422 the input voltage VIN has to change to R2 ∆V PIN 4 = ∆VIN R1 + R2 (8) With the value of the relationship of the resistors R1 and R2 R1 ∆VIN − ∆V PIN 4 = R2 ∆V PIN 4 (9) the additional offset current can be calculated as I SET = I OUTmin − I INmin = I OUTmin − VINmin R2 2 R0 R1 + R2 (10) The value of the set resistor can then be found using equation 4 In respect to the load resistor RL, the value of the supply voltage VS has to be considered with care. The following relation is generally valid (see equation 1): VS ≥ IOUTmax RL +VCCmin . (11) The resulting operating range is indicated in Figure 4. Sample calculations and typical values for the external components are listed in the Application Notes (beginning page 8). VCCmin = 6V RL [Ω] V − VCCmin RL ≤ S IOUTmax RLmax = 500Ω IOUTmax = 20mA 500 300 Operating Area 0 0 6 12 16 24 35 VS [V] Figure 4 analog microelectronics April 99 6/10 VOLTAGE/CURRENT CONVERTER AM422 PINOUT PIN VCC 1 8 VREF RS 2 7 GND OUT 3 6 VSET VIN 4 5 SET Figure 5 NAME DESIGNATION 1 VCC Supply Voltage 2 RS Sense Resistor 3 OUT Output 4 VIN Voltage Input 5 SET Set Voltage 6 VSET Reference Voltage Select 7 GND IC Ground 8 VREF Reference Voltage Output DELIVERY The AM422 is available in 2– (AM422–2) or 3–wire version (AM422–1). The different versions are pin compatible. The AM422 is available as: • 8 pin DIL packages (samples) • SO 8 packages • Dice on 5“ blue foil PACKAGE DIMENSIONS SOP8 4,98 ± 0,1 4,0 + 0,2 - 0,1 1,45 ± 0,1 ≤ 2,00 0,2 ± 0,05 0,2 ± 0,1 ≤ 0,635 1,27 0,42 ± 0,07 ≥ 0,3 0°-10° 6,2 ± 0,2 8 1 4 Figure 6 analog microelectronics April 99 7/10 VOLTAGE/CURRENT CONVERTER AM422 TYPICAL THREE–WIRE APPLICATION (0 – 5/10V) R3 VREF 6 RSET C1 8 AM422−1 VS 5 VSET R4 VREF 2 G=1 VOFFSET 5/10 V Reference 1 R0 2 V VIN Amplifier 4 I R1 7 R2 3 T1 D1 IOUT R5 RL Ground Figure 7 Used in a three–wire circuit (AM422–1) ground pin 7 (GND) is connected to Ground (Figure 7). The relationship of R1/R2, using equation 2, becomes R1 VINmax = −1 R2 2 R0 ( I OUTmax − I SET ) The current ISET is used to set the output current offset and can be calculated by using equation 3 I SET (VIN = 0) = VREF ( R4 + RSET ) − R3 ⋅ R0 2 ( R3 + R4 + RSET ) With R3 = R4 the set resistor RSET becomes (equation 4) RSET ≈ 4 R0 R4 I SET VREF Example 1: Output current range 4...20mA In this case the values of the external devices (VIN = 0K5V , VREF = 5V ) are as follows R0 = 25Ω R3 = R4 = 33kΩ RSET ≈ 2.64kΩ R5 = 40Ω R1/R2 ≈ 5.25 RL = 0...500Ω C1 = 2.2µF Example 2: Output current range 0...20mA In this case the values of the external devices (VIN = 0K10V , VREF = 5V ) are as follows R0 = 25Ω R3 = R4 = 33kΩ RSET = 0Ω R5 = 40Ω R1/R2 ≈ 9 RL = 0...500Ω C1 = 2.2µF analog microelectronics April 99 8/10 VOLTAGE/CURRENT CONVERTER AM422 TYPICAL THREE–WIRE APPLICATION (0.5 – 4.5V) C1 VREF R3 6 RSET 5 VSET R4 Sensor 0.5−4.5V 8 AM422−1 VREF 2 G=1 VOFFSET VS 5/10 V Reference 1 R0 V 2 VIN 4 Amplifier I R1 3 7 R2 T1 D1 IOUT R5 RL Ground Figure 8 Example 3: Output current range IOUT = 4...20mA, input voltage range VIN = 0.5...4.5V The transfer function of the output current IOUT is (equation 2) V R2 I OUT = I SET + I IN = I SET + IN 2 R0 R1 + R2 For the 0.5 to 4.5V application (Figure 8) a change of the input voltage from ∆VIN = 4V should be displayed over a change of the output current ∆IOUT = 16mA. With the voltage change at pin 4 (∆VPIN4 = 800mV, equation 7) the relationship of R1/R2, using equation 8, becomes then ∆V PIN 4 R2 800mV = = ∆VIN R1 + R2 4V ⇒ R1 ∆VIN − ∆V PIN 4 = =4 ∆V PIN 4 R2 With that relation an offset current ISET from I SET = I OUTmin − I INmin = I OUTmin − 2mA = 2mA has to be adjusted (equation 10). With R3 = R4 the set resistor RSET can be calculated (equation 4) RSET ≈ 4 R0 R4 I SET VREF The values of the external devices than can be calculated as follows (VREF = 5V ) R0 = 25Ω R1/R2 ≈ 4 C1 = 2.2µF R3 = R4 = 33kΩ R1 ≈ 68kΩ RSET ≈ 1.32kΩ R2 ≈ 18kΩ analog microelectronics R5 = 40Ω RL = 0...500Ω April 99 9/10 VOLTAGE/CURRENT CONVERTER AM422 TYPICAL TWO–WIRE APPLICATION (0 – 1V) R3 VREF 6 RSET C1 8 AM422−2 VS 5 VSET R4 VREF 2 G=1 VOFFSET 5/10 V Reference 1 C2 R0 2 V VIN Amplifier 4 I R1 7 R2 3 T1 D1 IOUT R5 RL Ground Figure 9 Used in a two–wire circuit (AM422–2) ground pin 7 (GND, ⊥) is connected between R5 and the load resistor (Figure 9). The relationship R1/R2, using equation 2, becomes R1 VINmax = −1 R2 2 R0 ( I OUTmax − I SET ) The current ISET is used to set the output current offset and can be calculated by using equation 3 I SET (VIN = 0) = VREF ( R4 + RSET ) − R3 ⋅ R0 2 ( R3 + R4 + RSET ) With R3 = R4 the set resistor RSET becomes (equation 4) RSET ≈ 4 R0 R4 I SET VREF Example 4: Output current range 4...20mA In this case the values of the external devices (VIN = 0...1V) are as follows R0 = 25Ω R3 = R4 = 33kΩ RSET ≈ 2.64kΩ R5 = 40Ω R1/R2 ≈ 0.25 RL = 0...500Ω C1 = 2.2µF C2 = 100nF The information provided herein is believed to be reliable; however, Analog Microelectronics assumes no responsibility for inaccuracies or omissions. Analog Microelectronics 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 licences to any of the circuits described herein are implied or granted to any third party. Analog Microelectronics does not authorise or warrant any Analog Microelectronics product use in life support devices and/or systems. analog microelectronics April 99 10/10