AM452

AM452 AME | Alldatasheet

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AM452 – Voltage-to-current transducer IC with a differential input Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz February 2008 - Rev 1.2 - Page 1/21 Phone: +49 (0)6131/91 073-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de PRINCIPLE FUNCTION Amplification and conversion of differential input voltages (±400mV with a CMIR offset and maximum output currents are independently adjustable in a wide range. The IC is suitable for both 2- and 3-wire applications and as a HART® carrier IC. TYPICAL APPLICATIONS Transducers for differential input signals in current output values for:

• Transducers for sensor applications with an internal sensing element supply
• Drivers for the analog industrial power grid (e.g. remote display in current loop operation)
• Differential impedance converters
• Carrier for standard HART® protocol communications
• Modular signal conditioning with digital correction (Frame concept [1]) VCC = 6…35V IS = max 10mA Differential input mV00± 4 VREF= 5/10V

AM452 – Voltage-to-current transducer IC with a differential input Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz February 2008 - Rev 1.2 - Page 2/21 Phone: +49 (0)6131/91 073-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de TABLE OF CONTENTS PRINCIPLE FUNCTION 1 FEATURES 3 SCHEMATIC 3 GENERAL DESCRIPTION 3 ELECTRICAL SPECIFICATIONS 4 BOUNDARY CONDITIONS 7 DETAILED DESCRIPTION OF FUNCTIONS 8 Instrumentation amplifier (IA) 8 Operational amplifier stage (OP1) 8 Zero adjust stage 8 SET stage 8 Voltage-to-current converter (V/I converter) 8 Reference voltage source 8 Additional operational amplifier OP2 8 OPERATING AM452 8 2- and 3-wire applications in general [2] 8 Differences in the AM452 circuitry with 2- and 3-wire applications 8 Selecting the supply voltage 8 Setting the offset and output current range for VIN = 0 8 OPERATING AM452: IMPORTANT POINTS TO NOTE 8 DIMENSIONING 8 APPLICATIONS 8 Typical 3-wire application with a differential input signal 8 Typical 2-wire application with a differential input signal 8 Offset compensation using a voltage divider at SET stage 8 Using OP2 as a current source 8 Using OP2 as a voltage source 8 BLOCK DIAGRAM AND PINOUT 8 DELIVERY 8 PACKAGE DIMENSIONS 8 FURTHER READING 8 NOTES 8

AM452 – Voltage-to-current transducer IC with a differential input Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz February 2008 - Rev 1.2 - Page 4/21 Phone: +49 (0)6131/91 073-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de ELECTRICAL SPECIFICATIONS Tamb = 25°C, VCC = 24V, VREF = 5V, IREF = 1mA (unless otherwise stated) Parameter Symbol Conditions Min. Typ. Max. Unit Supply Voltage Range VCC VSET not connected 6 35 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 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 Current IREF * 0 10.0 mA VREF vs. Temperature d VREF/dT Tamb = - 40...+85°C ±90 ±140 ppm/°C Line Regulation d VREF/dV VCC = 6V...35V 30 80 ppm/V d VREF/dV VCC = 6V...35V, IREF ≈ 5mA 60 150 ppm/V Load Regulation d VREF/dI 0.05 0.10 %/mA d VREF/dI IREF ≈ 5mA 0.06 0.15 %/mA Load Capacitance CL 1.9 2.2 5.0 µF Current/Voltage Source OP2 Internal Reference VBG 1.20 1.27 1.35 V VBG vs. Temperature d VBG/dT Tamb = - 40...+85°C ±60 ±140 ppm/°C Current Source: ICV = VBG/REXT Adjustable Current Range* ICV * 0 10 mA Output Voltage VCV V CC < 19V VBG VCC – 4 V VCV VCC ≥ 19V VBG 15 V Voltage Source: VCV = VBG (REXT1 + REXT2) / REXT2 Adjustable Voltage Range VCV V CC < 19V 0.4 VCC – 4 V VCV VCC ≥ 19V 0.4 15 V Output Current ICV * Source 10 mA ICV Sink –100 µA Load Capacitance CL Source mode 0 1 10 nF * In 2-wire operation IS has to fulfill the condition ICC +IS < IOUTmin with IOUTmin = 4mA

AM452 – Voltage-to-current transducer IC with a differential input Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz February 2008 - Rev 1.2 - Page 5/21 Phone: +49 (0)6131/91 073-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de Parameter Symbol Conditions Min. Typ. Max. Unit Instrumentation Amplifier (cont.) Internal Gain GIA 4.9 5 5.1 Differential Input Voltage Range VIN 0 ±400 mV Common Mode Input Range CMIR V CC < 9V, ICV < 2mA 1.5 VCC – 3 V CMIR VCC ≥ 9V, ICV < 2mA 1.5 6.0 V Common Mode Rejection Ratio CMRR 80 90 dB Power Supply Rejection Ratio PSRR 80 90 dB Offset Voltage VOS -9.0 -1.5 +6.0 mV VOS vs. Temperature d VOS/dT ±5 µV/°C Input Bias Current IB –100 –250 nA IB vs. Temperature d IB/dT –0.4 –0.9 nA/°C Output Voltage VOUTIA VCC < 9V VCC – 4 V VOUTIA VCC ≥ 9V 5 V Minimum Output Voltage VOUTIAmin 4.5 16 mV Load Capacitance CL 250 pF Zero Adjust Stage Internal Gain GZA 0.94 1 1.06 VZA ≤ VOUTIAmax – GIA ∆VIN ; Vcc<9V, ∆VIN=400mV, GIA=5

0 Vcc-6 V Zero Adjust Voltage VZA

VZA ≤ VOUTIAmax – GIA ∆VIN; Vcc≥9V, ∆VIN =400mV, GIA=5 0 3 V Offset Voltage VOS ±0.5 ±2.0 mV VOS vs. Temperature d VOS/dT ±1.6 ±5 µV/°C Input Bias Current IB 47 120 nA IB vs. Temperature d IB/dT 18 30 pA/°C Operational Amplifier – Gain Stage (OP1) Adjustable Gain GGAIN 1 Input Range IR V CC < 10V 0 VCC – 5 V IR VCC ≥ 10V 0 5 V Power Supply Rejection Ratio PSRR 80 90 dB Offset Voltage VOS -3.0 -1.0 1.0 mV VOS vs. Temperature d VOS/dT ±3 ±7 µV/°C Input Bias Current IB 10 25 nA IB vs. Temperature d IB/dT 7 20 pA/°C Output Voltage Limitation VLIM VREF V Output Voltage Range VOP VCC < 10V 0 VCC – 5 V VOP VCC ≥ 10V 0 VREF V Load Capacitance CL 250 pF NB: The current in the IC is given as a negative quantity.

AM452 – Voltage-to-current transducer IC with a differential input Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz February 2008 - Rev 1.2 - Page 6/21 Phone: +49 (0)6131/91 073-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de Parameter Symbol Conditions Min. Typ. Max. Unit V/I Converter Internal Gain GVI 0.122 0.125 0.128 Trim Range Adjustable by R0 0.60 1.00 1.40 Voltage Range at R0 FS VR0FS 320 540 760 mV Offset Voltage VOS βF ≥ 100 ±2 ±4 mV VOS vs. Temperature d VOS/dT βF ≥ 100 ±7 ±14 µV/°C Input Resistance RIN 120 160 kΩ RIN vs. Temperature d RIN/dT 0.2 0.3 kΩ/°C Output Offset Current IOUTOS 3-wire operation –25 –35 µA IOUTOS vs. Temperature d IOUTOS/dT 3-wire operation 16 26 nA/°C Output Offset Current IOUTOS 2-wire operation 9.5 14 µA IOUTOS vs. Temperature d IOUTOS/dT 2-wire operation 6 8 nA/°C Output Control Current IOUTC 2-wire operation, VR0/100mV 6 8 µA IOUTC vs. Temperature d IOUTC/dT 2-wire operation –10 –15 nA/°C Output Voltage Range VOUT V OUT = RL IOUT, VCC < 18V 0 VCC – 6 V VOUT VOUT = RL IOUT, VCC ≥ 18V 0 12 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 SET Stage Internal Gain GSET 0.5 Input Voltage VSET 0 1.15 V Offset Voltage VOS -4.0 -1.0 +2.0 mV VOS vs. Temperature d VOS/dT ±1.6 ±5 µV/°C Input Bias Current IB 8 20 nA IB vs. Temperature d IB/dT 7 18 pA/°C Protective Functions Voltage Limitation at R0 VLIMR0 VR0 = VIN GI, SET = GND VREF/8 mV VLIMR0 VIN = 0, VR0 = VSET/2 580 635 690 mV Protection against reverse polarity Ground vs. VS vs. VOUT 35 V Ground vs. VS vs. IOUT 35 V Current in event of reverse polarity Ground = 35V, VS = IOUT = 0 4.5 mA System Parameters Nonlinearity Ideal input 0.05 0.15 %FS 3-dB-frequency f3db RL = 600Ω, C2 = 1nF 5 kHz Statistical output impedance Rstat. RL =600Ω, C2 = 1nF, 4·10 3 M Ω Dynamical output impedance Rdyn. For f= 2,2kHz, RL =600Ω, C2 = 1nF, 3·10 3 Ω Table 1: Specifications

AM452 – Voltage-to-current transducer IC with a differential input Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz February 2008 - Rev 1.2 - Page 8/21 Phone: +49 (0)6131/91 073-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de DETAILED DESCRIPTION OF FUNCTIONS AM452 is a modular, monolithically integrated transducer which has been specially developed for the conditioning of differential voltage signals. It consists of several function blocks, the values of which are described in deta il in the electrical specifications. Its various function blocks are depicted in the block diagram (Figure 2) and described in the following. Instrumentation amplifier (IA) The instrumentation amplifier (IA) with an internal fixed gain of GIA = 5 acts as an input stage for differential voltage si gnals of ± 400mV maximum. Th anks to the device's special construction a high input impedance and high common mode rejecti on ratio (CMRR) are achieved. The reference potential of the amp lifier can be set externally using pin 13 or ZA, with which the offset current at the output (e .g. 4mA) can be increased. It is thus possible to compensate for the negative offset of the si gnal source (up to -400mV) or to correct that of the instrumentation amplifier. The following applies to the transfer function of the instrumentation amplifier: ZAINIAOUTIA VVGV += with 0>OUTIAV (1) where VIN describes the differential vo ltage between the two inputs V IN+ and VIN- and VZA the voltage at pin 13 (ZA) of instrumentation amplifier IA. Operational amplifier stage (OP1) The operational amplifier stage (OP1) permits variable amplification of the IA output signal. OP1 gain GGAIN can be set via external resistors R1 and R2 (see Figure 2). Protective circuitry against overvoltage is integrated into the chip, limiting the voltage to the set value of the reference voltage. The output voltage at OP1 can be tapped for control purposes at pin 7 (VOP). This is calculated as: GAINOUTIAOP GVV ⋅= with   += 1 R RGGAIN (2) where OUTIAV is not externally accessible but is connected internally to the OP1 input. Zero adjust stage The zero adjust stage enables a negative signal to be raised to a maximum of -400mV at the instrumentation amplifier input by adding an additional voltage of V ZA. A zero setting which is practically offset free with regard to the following circuit modules can thus be achieved, for example. The following applies: INIAOUTIAZA VGVV ∆−≤ max

AM452 – Voltage-to-current transducer IC with a differential input Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz February 2008 - Rev 1.2 - Page 9/21 Phone: +49 (0)6131/91 073-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de SET stage The SET stage permits the adjustment of the offset output current I OUTmin > 0mA. Together with the V/I converter it effects the output current I OUT. Via pin 16 ( SET) an offset current ISET can be set at pin 8 (IOUT) e.g. with the help of the inte rnal voltage reference and an external voltage divider as shown in Figure 2, for example. Voltage-to-current converter (V/I converter) The voltage-to-current converter (V/I converter) compares the voltage drop across the external sensing resistor R0 with a value of VSET GSET + VOP GVI and uses the result to regulate transistor T1. It generates a suitable signal at the IC output pin 8 (IOUT) which activates external transistor T1. This in turn supplies an output current of IOUT and accepts the power dissipation of the output stage. External resistor R0 permits the output current to be finely adjusted. For the output current IOUT amplified by T1 the following ratio applies: SET VIOP OUT IR GVI +⋅= = SET OP IR V + 08 with GVI SETSET SET ⋅= = 02R VSET (3)/(4) where VOP is the input voltage of the V/I converter and VSET the voltage at pin 16 (SET). Reference voltage source The reference voltage s ource (bandgap voltage source) enab les voltage to be supplied to external components (such as sensors, micropro cessors, etc.). The re ference voltage value VREF can be set using pin 12 ( VSET). If pin 12 is not connected, VREF = 5V; if pin 12 is switched to ground, VREF = 10V. Values between these can be set if two external resistors are used (inserted between pin 15 ( VREF) and pin 12 ( VSET) and between pin 12 ( VSET) and GND). External capacitor C1 stabilizes the reference voltage. It must be connected even if the voltage reference is not in use. It may not undershoot the given minimum value. Additional operational amplifier OP2 The additional operational amplifier OP2 can be used as a current or voltage source to supply external components. OP2's positive inpu t must be connected internally to bandgap voltage VBG so that the OP2 output voltage at pin 1 or CVREF can be set across a wide range using external resistors. The individual modules are described separately in the specifications. The reference voltage source and the operational amplifier OP2 can be operated as independent circuit elements or modules. Instrumentation amplifier IA, operational amplifier OP1 and the V/I converter form a unit within the circuit and have the task of converting the voltage input signal into the required output current.

AM452 – Voltage-to-current transducer IC with a differential input Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz February 2008 - Rev 1.2 - Page 10/21 Phone: +49 (0)6131/91 073-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de OPERATING AM452 2- and 3-wire applications in general [2] As AM452 can function in both 2- and 3-wire operation through external contacting, it is important to first differentiate between the two versions of the circuit. In 2-wire operation the IC ground is "virtual" (floating), as with a constant load resistance the IC supply voltage VCC changes according to the current. The following equation can generally be applied to 2-wire operation: ( ) LINOUTSCC RVIVV −= (5) The reason for this is that in 2-wire operation the IC is connected in series to the actual load resistor RL. This is illustrated in Figure 3. In a 2-wire system the power consumption of the overall syst em (AM452 plus all external components including the signal source and adju sting resistors) may not be more than IOUTmin (e.g. 4mA). In 3-wire operation Equation (5 ) no longer applies as the IC ground is connected to the ground of the system. In 3-wire operation the supply voltage can be expressed as: VCC = VS (6) RL VS 2-wire system signal source and conditioning IC GND Ground ≠ VCC ≠ VS Ground RL 3-wire system signal source and conditioning IC GND Ground = VCC = VS Ground GN D = GND VCC IOUT IOUT VVCC S= Figure 3: The basic difference between a 2- and 3-wire circuit NB: The difference between GND and Ground must be clearly acknowledged!

AM452 – Voltage-to-current transducer IC with a differential input Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz February 2008 - Rev 1.2 - Page 11/21 Phone: +49 (0)6131/91 073-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de Differences in the AM452 circuitry with 2- and 3-wire applications Figure 4: Differences in 2-and 3-wire circuitry in conjunction with AM452 AM452 is constructed in such a way that by cha nging the external circuitry it is suitable for both 2-wire and 3-wire operation. In 3-wire operation (see Figure 4, right) the IC's connection to ground (pin 14 or GND) is connected to the system ground ( Ground) which is applied externally. System supply voltage V S is connected to pin 10 ( VCC) and pin VCC to pin 11 ( RS+). Supply current I CC then flows directly into AM452 (power consumption). In 2-wire operation (see Figure 4, left) system supply voltage VS is connected to pin 11 ( RS+) and pin 10 ( VCC) to pin 9 ( RS-). The overall current including the supply current then flows via R0, enabling the relevant voltage drop to be used to regulate transistor T1. The IC's connection to ground pin 14 ( GND) is contacted to the node between resistor R5 and load resistor RL (current output IOUT). IC ground GND is thus not the same as the ground of the system ( Ground). The output signal is tapped via load resistor RL which links system output IOUT to the ground of the system. Ground VS IOUT RL GND SET Stage 3-wire connection V/I Converter Ground VS IOUT RL 2-wire connection GND V/I Converter SET Stage

AM452 – Voltage-to-current transducer IC with a differential input Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz February 2008 - Rev 1.2 - Page 12/21 Phone: +49 (0)6131/91 073-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de Selecting the supply voltage "System" supply voltage VS needed to operate AM452 is dependent on the selected mode of operation. The word "system" here refers to the IC plus its external circuitry. When using current output pin 8 ( IOUT) in conjunction with the external transistor VS is dependent on the relevant load resistor RL used by the application. The following is then applicable to the minimum system supply voltage VS: minmax CCLOUTS VRIV +≥ (7) Here, IOUTmax stands for the maximum output current and VCCmin for the minimum IC supply voltage which is dependent on the selected reference voltage: V1min +≥ REFCC VV (8) For the 3-wire version the load resistance is limited to RLmax = 600 Ω due to the condition: VOUT max = 12V @ VCC ≥ 18V. Equation 7 is also valid for the 2- wire version; he re, however, the RLmax = 600 Ω limitation does not apply. Here, load resistor RLmax = 900Ω when VS = 24V. Setting the offset and output current range for VIN = 0 When adjusting AM452 a preset should first be made. To this end the offset of the output current is compensated for, in which the two IA inputs are first short-circuited ( VIN = 0) and then both set to a permitted potential (c.f. CMIR in ELECTRICAL SPECIFICATIONS). With the short-circuit at the input the following is derived from Equations (3) and (4) when the voltage divider from R3 and R4 is taken into account for reference voltage VREF (see Figure 2, for example): VS [V] RL [Ω] 6 35 VCCmin = 6V RLmax = 600Ω IOUTmax = 20mA R VV IL SC C min OUTmax ≤ − 2412 600 Operating range 300 Figure 5: Working range in conjunction with the load resistor in 3-wire operation In Equation (7) of Figure 5 the ohmic resistance of power supply lines RR is not taken into consideration. This is entered as an additive quantity (IOUT max RR) to the calculation of VS in Equation (7).

AM452 – Voltage-to-current transducer IC with a differential input Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz February 2008 - Rev 1.2 - Page 13/21 Phone: +49 (0)6131/91 073-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de () SETINOUT IVI == 0 with 02 RR R R VI REF SET +⋅= → 12 04 3 −⋅⋅= SET REF IR V R R (9) The output current range (e.g. 16mA) is set by the selection of external resistors R1 and R2 (or fine adjustment with R0 ). Output current IOUT is then calculated as: SET VII INOUT IR GGVI +⋅= with GAINIAI GGG ⋅= and 0=ZAV (10) If the offset of the AM452 signa l source and input amplifier (IA) is such that it cannot be ignored, when setting the output current range (gain) ( )0=INOUT VI also changes. This shift must possibly be accounted for by making a fine adjustment to R 3 and R4. If the offset of the signal source and input amplifier is not relevant to the required degree of precision, Equations (9) and (10) continue to apply. OPERATING AM452: IMPORTANT POINTS TO NOTE 1. When using AM452 it is impera tive that exte rnal capacitor C1 (a ceramic capacitor) is always connected. Care must be taken that the va lue of the capacitor does not exceed the range of values given in the boundary conditions – also within the temperature range (see Table 2). In 2-wire operation ceramic capacitor C2 must also be used. 2. All AM452 function blocks not required by th e application (OP2 or VREF) must be placed in a defined (and allowed) operating state. 3. The voltages at the IA inputs (pins IN+ and IN-) must always lie within input voltage range CMIR. 4. At the current output a load resistance of 600 Ω maximum is permissible for 3-wire operation. 5. The values of external resistors R0, R1, R2, R3, R4, R5, R6 and R 7 must be selected within the permissible range given in the boundary conditions. 6. The tolerances of the resistors and their te mperature coefficients are entered into the overall error. 7. In order to avoid temperature gradients it is imperative that the transistor is placed far enough away from IC AM452 and that a sufficient temperature outlet is ensured. 8. In a 2-wire setup with a minimum output (offset) current of I OUT min the current balance (the total domestic power supply across a temperature range of < IOUT min) of the IC and all connected components (such as sensors) must be taken into account.

AM452 – Voltage-to-current transducer IC with a differential input Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz February 2008 - Rev 1.2 - Page 14/21 Phone: +49 (0)6131/91 073-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de 9. For applications where I OUT min > 0mA (e.g. 4mA) in both 2- and 3-wire applications the following condition applies to the IA input values: min max OUT OUT IAOS IAFS I I V V ≥ , where VFS.IA is the maximum input signal and VOS.IA the positive offset at the input IA. 10. If signal source and/or input amplifier IA have a negative offset this can be compensated for using corrective voltage VZA and a suitable voltage divider (R6 and R7; see Figure 2). DIMENSIONING Two possible dimensioning methods are suggested here. Dimensioning the external components acco rding to the equations given in the data sheet Dimensioning according to the equations given in the data sheet enables all modules to be used, making it possible for the setup to be adapted to suit the most diverse application requirements. As a rule the offset of the AM452 input signal must be taken into account. If an input signal offset is present and an offset current of I OUT min > 0mA is required, the following boundary condition then applies: min max OUT OUT IAOS IAFS I I V V ≥ , where VFS.IA is the maximum input signal and VOS.IA the positive offset at the input IA (see: chapter before). Should the signal source have a negative offset, the offset can be set via pin 13 (ZA) and voltage divider R6 and R7 (see Figure 2). Equation (1) forms the basis for all other equations in this particular case. If the offset is negligible, Equations (9) and (10) apply. See the following applications for further details. Dimensioning AM452's external components using an Excel spreadsheet AM452's external components can also be dimens ioned with the help of Excel spreadsheet Kali_AM452.xls when the input signal is positive (see [3]). The algorithm is such that the offset output current of 4mA can only be set via pin 13 (ZA) of the zero adjust stage. The SET stage is not active. The full-scal e output current is set to 20 mA using the OP1 gain setting. The calibration process is also based on the condition that the output signal should be a 4...20mA current loop signal in 2-wire operation.

AM452 – Voltage-to-current transducer IC with a differential input Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz February 2008 - Rev 1.2 - Page 16/21 Phone: +49 (0)6131/91 073-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de Here, GI is the overall gain of the instrumentation amplifier (IA) and the back-end operational amplifier (OP1). ISET is the additional offset current whic h is set using a vo ltage at the SET pin and which can raise the output current of the VI/ converter by a constant value. For a measuring bridge with a signal of VIN = 0...100mV (without an of fset) at the IA input the external components should be dimensioned in such a way that output current I OUT is 4...20mA. If the input signal offset is negligible, resistors R 0, R 1, R 2, R 3 and R 4 must be determined. With the two voltage dividers it is sufficient to calculate just one of the two resistors; the other can be selected within the stipulations give n by the boundary condition s. In this example a value of 5V has been selected for VREF, with 10k Ω chosen for R 2 and 5k Ω for R 4. With a current of 20mA the voltage should drop by a typical value of 540 mV at resistor R 0. The following is accrued: VAR 54.002.00 =⋅ ( 1 3 ) With reference to Equations (11) and (12) and the values given in Example 1 the following is obtained: ( ))5( )101(51.0 02.0 300 Ω⋅⋅+⋅ Ω+⋅⋅ = kR k R V R k RV A )5( 5004.0 30 Ω+ Ω⋅⋅= kR k R VA By solving the above system of equations and taking the given defaults into account, the following values are computed for the 3-wire, 4–20mA current interface: R0 = 27Ω R1 = 59.12kΩ R 2 = 10kΩ R3 = 110.74kΩ R4 = 5kΩ R 5 = 39Ω RL = 0...600Ω C1 = 2.2µF If the offset output current is not exactly 4mA due to component tolerances and deviates from this value, the voltage can be adjusted at pin 16 (SET) using voltage divider R 3 and R 4 (see Figure 7 ) and the output value th us corrected (c.f.: Offset compensation using a voltage divider at SET).

AM452 – Voltage-to-current transducer IC with a differential input Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz February 2008 - Rev 1.2 - Page 17/21 Phone: +49 (0)6131/91 073-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de Typical 2-wire application with a differential input signal In order to determine the system resistors R0 to R5 must first be determined. For a measuring bridge with a signal of VIN = 0...100mV (without an offset) at the IA input the external components in the AM452 circuitry should be dimensioned in such a way that the output current range is 4...20mA. AM452 is configur ed in such a way that the entire current, including the chip's quiescent current, flows through R0 (example for the 2-wire application). As in Example 1, R 2 and R 4 can be freely selected within the boundary conditions. In this example a value of 10k Ω has been chosen for R 2, with 5kΩ selected for R 4. VREF = 5V. The value of R0 has been set to 33k Ω. Applying Equations (12) and (13) the values for R 1 and R3 are as follows: ( ))5( 332 338 )101(51.0( 02.0 Ω⋅Ω⋅+Ω⋅ Ω+⋅⋅ = kR kk RV A )5( 332 5004.0 3 Ω+ Ω⋅Ω⋅= kR kA Ground VS IOUT R3 R4 RL RSET GND VBG IA 1413 V oltage Reference OP1 AM452 OP2 GVI GSET SET Stage ZERO Stage V/I Converter IC ground: GND System ground: Ground different potentials! 2-wire connection Figure 7: Typical 2-wire application for differential input signals

AM452 – Voltage-to-current transducer IC with a differential input Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz February 2008 - Rev 1.2 - Page 19/21 Phone: +49 (0)6131/91 073-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de Using OP2 as a current source The additional operational amplifier OP2 can easily be configured as a constant current source. Using the circuitry shown in Figure 8 the following equation is generated: SS BG S RR VI V27.1== (14) The bridge symbol is supposed to represent th e component to be supplied with current (such as a piezoresistive sensing element or a temperature sensor, for example). Example: A supply current of IS = 1mA is to be set. Using E quation (14) the below value is accrued for external resistor RS, which determines the quantity of current: Ω=== k27.1mA1 V27.1 S BG S I VR Using OP2 as a voltage source In addition to the integrated voltage referen ce OP2 can also be used to supply voltage to external components such as A/ D converters or microprocessors, for example. This permits lower supply voltages of 3.3V, for example, to be generated. The following is derived from the circuitry in Figure 9:  +=  += 6 1V27.11 R R R RVV BGCVREF (15) Example: A voltage of VCVREF = 3.3V is to be set. Using Equation (15) the following ratio is provided for external resistors R6 and R7: 6.116.21 6 =−≈−= BG CVREF V V R R Example values of R7 = 10kΩ and R6 = 16kΩ are accrued for the resistors.

AM452 – Voltage-to-current transducer IC with a differential input Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz February 2008 - Rev 1.2 - Page 20/21 Phone: +49 (0)6131/91 073-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de BLOCK DIAGRAM AND PINOUT Figure 10: Simplified block diagram Figure 10: Simplified block diagram Values which can be measured at the pins have indices; the pin name is written in capital letters. PIN NAME EXPLANATION

1 CVREF Current/Voltage reference

2 CVSET Current/Voltage reference set

3 IN+ Positive input

4 IN– Negative input

5 GAIN Gain set

6 NC Not connected

7 VOP OP1 output

8 IOUT Current output

9 RS– Sensing resistor –

10 VCC Supply voltage

11 RS+ Sensing resistor +

12 VSET Reference voltage source set

13 ZA Offset set

14 GND IC ground

15 VREF Reference voltage source output

16 SET Output offset current set

Table 3: Pinout 1 16 2 15 3 14 4 13 5 12 6 11 7 10 CVREF CVSET IN+ IN- GAIN NC VOP IOUT SET VREF GND ZA VSET RS+ VCC RS- AM 452 Figure 11: Pinout VREF IN+ IN- SET VOP GND VSET GAINZA IOUT RS+ RS- VCC CVREF CVSET VBG IA 5 14 1612 15 Volta ge R ef e ren ce OP1 AM452 OP2 V/I Converter GSE T GVI

AM452 – Voltage-to-current transducer IC with a differential input Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz February 2008 - Rev 1.2 - Page 21/21 Phone: +49 (0)6131/91 073-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de DELIVERY AM452 is available as an:

• SO16(n) PACKAGE DIMENSIONS Please see the data sheet on our website: package.pdf FURTHER READING [1] The Frame ASIC concept: http://www.Frame-ASIC.de/ The following links refer to the Analog Microelectronics website: http://www.analogmicro.de/ [2] Technical article: PR1012 – AM462 Voltage-to-current converter IC for 2-wire current loop applications [3] Download: Kali_AM452.xls NOTES Analog Microelectronics reserves the right to make amendments to any dimensions, technical data or other information herein without further notice.