AM422

AM422 ANALOGMICRO | Alldatasheet

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VOLTAGE/CURRENT CONVERTER AM422 analog microelectronics April 99 Analog Microelectronics GmbH Phone: +49 (0)6131/91 073 – 0 1/10 An der Fahrt 13, D – 55124 Mainz Fax: +49 (0)6131/91 073 – 30 Rev. 2.1 Internet: www.analogmicro.de E–Mail: info@analogmicro .de

FEATURES

• Wide Supply Voltage Range: 6...35V
• Wide Operating Temperature Range: –40°C...+85°C
• Adjustable Voltage Reference: 4.5 to 10V
• Operational Amplifier Input:
• 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

APPLICATIONS

• Sensor Interface
• Industrial Process Control
• Programmable Current Source
• Current Source Reference GENERAL DESCRIPTION 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 al- lows 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 opera- tional amplifier input stage for single ended input signals (0.5–4.5V, 0–10V, or other), a programmable 4.5 to 10V reference for trans- ducer 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 trans- mission. DELIVERY
• DIL8 packages (samples)
• SOP8 packages
• Dice on 5“ blue foil BLOCK DIAGRAM VIN OUT RS SET VCC GND AM422 Input Amplifier G = 1VREF V I VREFVSET 6 8 Reference Voltage Figure 1

VOLTAGE/CURRENT CONVERTER AM422 analog microelectronics April 99 ELECTRICAL SPECIFICATIONS Tamb = 25°C, VCC = 24V, VREF = 5V, IREF = 1mA (unless otherwise noted) Parameter Symbol Conditions Min. Typ. Max. Unit Voltage Range VCC 63 5 V Quiescent Current ICC Tamb = – 40...+85°C, IREF = 0mA 1.5 mA Temperature Specifications Operating Tamb –40 85 °C Storage Tst –55 125 °C Junction TJ 150 °C Thermal Resistance Θja DIL8 plastic package 110 °C/W Θja SO8 plastic package 180 °C/W Voltage Reference Voltage VREF VSET not connected 4.75 5.00 5.25 V VREF VSET = GND, VCC ≥ 11V 9.5 10.0 10.5 V Trim Range VR10 4.5 VR10 V Current IREF*0 1 0 m A VREF vs. Temperature d VREF/dTT amb = – 40...+85°C ±90 ±140 ppm/°C Line Regulation d VREF/dVV CC = 6V...35V 30 80 ppm/V dVREF/dV VCC = 6V...35V, IREF ≈ 5mA 60 150 ppm/V Load Regulation d VREF/dI 0.05 0.10 %/mA dVREF/dI IREF ≈ 5mA 0.06 0.15 %/mA Load Capacitance CL 1.9 2.2 5.0 µF Set Stage Internal Gain GIA 1 Input Voltage VSET ISET = 4mA, R0 = 25Ω 2.6 V Offset Voltage VOS ±1 ±3m V VOS vs. Temperature d VOS/dT ±5µ V / ° C Input Bias Current IB 82 0 n A IB vs. Temperature d IB/dT 61 5 p A / ° C Input Stage Internal Gain GIN 0.5 Input Voltage VIN 01 . 1 5 V Offset Voltage VOS ±0.5 ±2.5 mV VOS vs. Temperature d VOS/dT ±1.6 ±5µ V / ° C Input Bias Current IB 82 0 n A IB vs. Temperature d IB/dT 71 8 p A / ° C

VOLTAGE/CURRENT CONVERTER AM422 analog microelectronics April 99 Parameter Symbol Conditions Min. Typ. Max. Unit V/I Converter Internal Gain GVI 1.00 Trim Range adjustable by R0 0.75 1.00 1.25 Voltage Range at R0 FS VR0FS 400 500 580 mV Offset Voltage VOS βF ≥ 100 ±2 ±6m V VOS vs. Temperature d VOS/dT βF ≥ 100 ±7 ±20 µV/°C Output Offset Current IOUTOS 3–wire operation –35 –50 µA IOUTOS vs. Temperature d IOUTOS/dT 3–wire operation 55 80 nA/°C Output Offset Current IOUTOS 2–wire operation 14 22 µA IOUTOS vs. Temperature d IOUTOS/dT 2–wire operation 22 35 nA/°C Output Control Current IOUTC 2–wire operation, VR0/100mV 5 µA IOUTC vs. Temperature d IOUTC/dT 2–wire operation –9 nA/°C Output Voltage Range VOUT VOUT = RL IOUT, VCC < 16V 0 VCC – 6 V VOUT VOUT = RL IOUT, VCC ≥ 16V 01 0 V Output Current Range FS IOUTFS IOUT = VR0/R0, 3–wire operation 20 mA Output Resistance ROUT 0.5 1.0 MΩ Load Capacitance CL 0 500 nF Protection Functions Voltage Limitation at R0 VLIMR0 VR0 = VIN/2, SET = VREF/2 580 635 690 mV VLIMR0 VIN = 0, VR0 = VSET/2 – VREF/2 580 640 700 mV Temperature Limitation TLIMIT 110 130 150 °C Protection against reverse polarity Ground vs. VS vs. IOUT 35 V Current in case of reverse polarity Ground = 35V, VS = IOUT = 0 3.8 mA System Parameters Nonlinearity ideal input 0.05 0.15 %FS * In 2–wire operation a maximum current of IOUTmin – ICC is valid Currents flowing into the IC are negative BOUNDARY CONDITIONS Parameter Symbol Conditions Min. Typ. Max. Unit Sense Resistor R0 IOUTFS = 2 0 m A 2 02 52 9 Ω R0 c = 20mA/IOUTFS c ⋅ 20 c ⋅ 25 c ⋅ 29 Ω Stabilisation Resistor R5 IOUTFS = 2 0 m A 3 54 04 5 Ω R5 c = 20mA/IOUTFS c ⋅ 35 c ⋅ 40 c ⋅ 45 Ω Load Resistance RL limitation only for 3–wire operation 0 500 Ω Sum Offset Resistors R3 + R4 20 200 kΩ VREF Capacitance C1 1.9 2.2 5.0 µF Output Capacitance C2 only for 2–wire operation 90 100 250 nF D1 Breakdown Voltage VBR 35 50 V T1 Forward Current Gain βF 50 150

VOLTAGE/CURRENT CONVERTER AM422 analog microelectronics April 99 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: VV IRCC S OUT L=− ⋅ (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 resis- tors 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 () ( ) ( )IV V I V I VO U TS E TI N S E TS E T I NI N, =+ (2) For the adjustment of the AM422 two cases have to be differentiated. For input voltage ranges The minimum output current has to be set with an input voltage V IN = 0V. The output offset current becomes () () IV R V VV R RR R RRRSET IN SET REF REF SET SET == ⋅ −     =⋅ +− ++0 1 2 200 () (3) With R3 = R4 and simplifications the set resistor RSET is R RRI VSET SET REF ≈ 4 04 (4) The output current range has to be set with the transfer function of the IC and can be calculated by ∆II I V R R RROUT OUTmax SET INmax=− = +   2 0 (5) The relationship of R1/R2 becomes R R V RI I INmax OUTmax SET 2 02 − (6) follows. For a desired change of the output current of ∆IOUT ∆ ∆I V ROUT PIN= 4 02 ⇒∆ ∆ VR IPIN OUT40 2= (7)

VOLTAGE/CURRENT CONVERTER AM422 analog microelectronics April 99 the input voltage VIN has to change to ∆∆VV R RRPIN IN4 = +    (8) With the value of the relationship of the resistors R1 and R2 R R VV V IN PIN PIN = −∆∆ ∆ (9) the additional offset current can be calculated as II I I V R R RRSET OUTmin INmin OUTmin INmin=− =− +   2 0 (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): VI RVS OUTmax L CCmin≥+ . (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). VS [V] RL [Ω] 6 35 VCCmin = 6V RLmax = 500Ω IOUTmax = 20mA R VV IL SC C m i n OUTmax ≤ − 2412 500 Operating Area 300 Figure 4

VOLTAGE/CURRENT CONVERTER AM422 analog microelectronics April 99 PINOUT VCC RS OUT VIN VREF VSET SET GND Figure 5 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 PIN 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

0°-10°≥ 0,3 1,27 ≤ 2,00 4,98 ± 0,1 1,45 ± 0,1 0,2 ± 0,1 6,2 ± 0,2 4,0 + 0,2 - 0,1 0,2 ± 0,05 Figure 6

VOLTAGE/CURRENT CONVERTER AM422 analog microelectronics April 99 TYPICAL THREE–WIRE APPLICATION (0 – 5/10V) 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 R R V RI I INmax OUTmax SET 2 02 The current ISET is used to set the output current offset and can be calculated by using equation 3 () () IV V R RR R RRR SET IN REF SET SET == ⋅ +− With R3 = R4 the set resistor RSET becomes (equation 4) R RRI VSET SET REF ≈ 4 04 Example 1: Output current range 4...20mA In this case the values of the external devices (VIN = 05K V, VREF = 5V ) are as follows R0 = 25Ω R3 = R4 = 33kΩ RSET ≈ 2.64kΩ R5 = 40Ω Example 2: Output current range 0...20mA In this case the values of the external devices (VIN = 01 0K V, VREF = 5V ) are as follows R0 = 25Ω R3 = R4 = 33kΩ RSET = 0Ω R5 = 40Ω R1/R2 ≈ 9 RL = 0...500Ω C1 = 2.2µF R3 VREF VS IOUT RL Ground G = 1 Amplifier VREF VIN VSET VOFFSET RSET V I 5/10 V Reference AM422−1 R5D1 Figure 7

VOLTAGE/CURRENT CONVERTER AM422 analog microelectronics April 99 TYPICAL THREE–WIRE APPLICATION (0.5 – 4.5V) The transfer function of the output current IOUT is (equation 2) II I I V R R RROUT SET IN SET IN=+ =+ +   2 0 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 V R RR PIN IN 800 4= + = mV V ⇒ R R VV V IN PIN PIN 4= − =∆∆ With that relation an offset current ISET from II I ISET OUTmin INmin OUTmin=− =− 2mA = 2mA has to be adjusted (equation 10). With R3 = R4 the set resistor RSET can be calculated (equation 4) R RRI VSET SET REF ≈ 4 04 The values of the external devices than can be calculated as follows (VREF = 5V ) R0 = 25Ω R3 = R4 = 33kΩ RSET ≈ 1.32kΩ R5 = 40Ω R1/R2 ≈ 4 R1 ≈ 68kΩ R2 ≈ 18kΩ RL = 0...500Ω C1 = 2.2µF VREF VS IOUT RL Ground G = 1 Amplifier VREF VSET VOFFSET RSET V I 5/10 V Reference AM422−1 R5D1 VIN Sensor 0.5−4.5V Figure 8

VOLTAGE/CURRENT CONVERTER AM422 analog microelectronics April 99 TYPICAL TWO–WIRE APPLICATION (0 – 1V) 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 R R V RI I INmax OUTmax SET 2 02 The current ISET is used to set the output current offset and can be calculated by using equation 3 () () IV V R RR R RRR SET IN REF SET SET == ⋅ +− With R3 = R4 the set resistor RSET becomes (equation 4) R RRI VSET SET REF ≈ 4 04 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 R3 VREF VS IOUT RL Ground G = 1 Amplifier VREF VIN VSET VOFFSET RSET V I 5/10 V Reference AM422−2 R5D1 Figure 9 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.