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CURRENT CONVERTER IC
FEATURES
* Wide Supply Voltage Range: 6...35V * Wide Operating Temperature Range: -40C...+85C * Adjustable Reference Voltage Source: 4.5 to 10V * Wide Common Mode Range Instrumentation Amplifier * Adjustable Gain and Offset * Two-Wire Output: 4...20mA * Three-Wire Output: 0/4...20mA * Adjustable Output Current Range * Protection Against Reverse Polarity * Current Shutdown with Overvoltage * Shutdown with Excessive Temperature
AM402
GENERAL DESCRIPTION
AM402 is a monolithically integrated current converter which has been specially developed for the processing of differential bridge signals. AM402 is suitable for two- and threewire applications and has four function blocks. A high-precision instrumentation amplifier (IA) serves as an input stage. A reference voltage source, which can be adjusted to values of between 4.5 and 10V, excites external components and a voltage-controlled current output stage converts the voltage signal. It is thus possible to generate output currents which correspond to the normal industrial standards (0/4-20mA, 12 8mA).
DELIVERY APPLICATIONS
* Industrial Process Control * Sensor Signal Converter (e.g. pressure) * Programmable Current Source * DIL16 packages (samples) * SO16(n) packages * Dice on 5" blue foil
BLOCK DIAGRAM
GAIN- GAIN GAIN+ 10 11 12 VSET 13 VREF 16
AM402
Reference Voltage 1 2 3
9 IN+ 8 IN- 14 GND 7 SET Instrumentation Amplifier
V I
RS+ VCC RS- OUT
5
Figure 1
analog microelectronics
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April 99 1/8 Rev. 2.1
CURRENT CONVERTER IC
ELECTRICAL SPECIFICATIONS
Tamb = 25C, VCC = 24V, VREF = 5V, IREF = 1mA (unless otherwise noted)
Parameter Voltage Range Quiescent Current Temperature Specifications Operating Storage Junction Thermal Resistance Tamb Tst TJ ja ja Voltage Reference Voltage VREF VREF Trim Range Current VREF vs. Temperature Line Regulation VR10 IREF* dVREF/dT dVREF/dV dVREF/dV Load Regulation dVREF/dI dVREF/dI Load Capacitance SET Stage Internal Gain Input Voltage Offset Voltage VOS vs. Temperature Input Bias Current IB vs. Temperature Instrumentation Amplifier Adjustable Gain Differential Input Voltage Range Common Mode Input Range GIA VIN CMIR CMIR Common Mode Rejection Ratio Power Supply Rejection Ratio Offset Voltage VOS vs. Temperature Input Bias Current IB vs. Temperature Input Offset Current IOS vs. Temperature Output Voltage Range FS Load Capacitance CMRR PSRR VOS dVOS/dT IB dIB/dT IOS dIOS/dT VOUTFS CL VOUTFS = VGAIN+ - VGAIN- 400 SET = GND VCC < 9V VCC 9V 1 0 1.5 1.5 80 80 90 90 1 5 8 6 0.2 0.8 500 5 GSET VSET VOS dVOS/dT IB dIB/dT 0 0.5 1.6 8 7 0.5 CL IREF 5mA 1.9 Tamb = - 40...+85C VCC = 6V...35V VCC = 6V...35V, IREF 5mA VSET not connected VSET = GND, VCC 11V 4.75 9.5 4.5 0 90 30 60 0.05 0.06 2.2 5.00 10.0 DIL16 plastic package SO16 narrow plastic package 70 140 -40 -55 Symbol VCC ICC Tamb = - 40...+85C, IREF = 0mA Conditions Min. 6 Typ.
AM402
Max. 35 1.5
Unit V mA
85 125 150
C C C C/W C/W
5.25 10.5 VR10 10 140 80 150 0.10 0.15 5.0
V V V mA ppm/C ppm/V ppm/V %/mA %/mA F
1.15 2.5 5 20 18
V mV V/C nA pA/C
580/GIA VCC - 3 6.0
mV V V dB dB mV V/C
3
20 15
nA pA/C nA pA/C
580 250
mV pF
analog microelectronics
April 99 2/8
CURRENT CONVERTER IC
Parameter V/I Converter Internal Gain Trim Range Voltage Range at R0 FS Offset Voltage VOS vs. Temperature Output Offset Current IOUTOS vs. Temperature Output Offset Current IOUTOS vs. Temperature Output Control Current IOUTC vs. Temperature Output Voltage Range VR0FS VOS dVOS/dT IOUTOS dIOUTOS/dT IOUTOS dIOUTOS/dT IOUTC dIOUTC/dT VOUT VOUT Output Current Range FS Output Resistance Load Capacitance Protection Functions Voltage Limitation at R0 Temperature Limitation Protection against reverse polarity Current in case of reverse polarity System Parameters Nonlinearity ideal input 0.05 VLIMR0 VLIMR0 TLIMIT Ground vs. VS vs. IOUT Ground = 35V, VS = IOUT = 0 3.8 VR0 = VIN GIA, SET = GND VIN = 0, VR0 = VSET/2 580 580 110 640 635 130 IOUTFS ROUT CL GVI adjustable by R0 0.75 400 1.00 1.00 500 2 7 -35 55 14 22 5 -9 0 0 20 0.5 0 1.0 Symbol Conditions Min. Typ.
AM402
Max. Unit
1.25 580 6 20 -50 80 22 35 mV mV V/C A nA/C A nA/C A nA/C VCC - 6 10 V V mA M 500 nF
F 100 F 100
3-wire operation 3-wire operation 2-wire operation 2-wire operation 2-wire operation, VR0/100mV 2-wire operation VOUT = RL IOUT, VCC < 16V VOUT = RL IOUT, VCC 16V IOUT = VR0/R0, 3-wire operation
700 690 150 35
mV mV C V mA
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 Sense Resistor Symbol R0 R0 Stabilisation Resistor R5 R5 Load Resistance Sum Gain Resistors Sum Offset Resistors VREF Capacitance Output Capacitance D1 Breakdown Voltage T1 Forward Current Gain RL R1 + R2 R3 + R4 C1 C2 VBR only for 2-wire operation Conditions IOUTFS = 20mA c = 20mA/IOUTFS IOUTFS = 20mA c = 20mA/IOUTFS limitation only for 3-wire operation Min. 20 c 20 35 c 35 0 25 20 1.9 90 35 50 2.2 100 50 150 Typ. 25 c 25 40 c 40 Max. 29 c 29 45 c 45 500 50 200 5.0 250 Unit k k F nF V
F
analog microelectronics
April 99 3/8
CURRENT CONVERTER IC
FUNCTIONAL DIAGRAMS
Reference Voltage
RA
AM402
3-Wire System
VS
V
VIN RIN
IA
IOUT
RB
I
RL
Ground
Figure 2
Reference Voltage
RA
2-Wire System
VS
V
VIN RIN
IA
IOUT
RB
I
RL
Ground
Figure 3
FUNCTIONAL DESCRIPTION
AM402 is a monolithically integrated current converter which has been specially developed for the processing of differential bridge signals. By varying a few external components, the output current can be set to various values within a wide range. Only an external output transistor T1 and a diode D1 are needed (See Figure 7 and Figure 8) in addition to the resistors R0 - R5 and the capacitor C1 (C2). The external transistor decreases the power dissipation of the IC and the diode protects the transistor against reverse polarity. The maximum power dissipation of the components must be taken into consideration when selecting the transistor and diode. Typical values for the external components are given in the following Description of Applications. AM402 can principally be used in the implementation of two- and three-wire systems for industrial applications. A schematic diagram illustrates a three-wire system in Figure 2. Here, the differential input voltage (VIN) is shown as a variable resistor. The external reference point Ground is identical to the ground of the IC (GND) and the supply voltage of the IC matches that of the system: VCC = VS. In two-wire configurations, however (Figure 3), the ground of the IC (GND) is connected between resistors R5 and RL. In this instance, the supply voltage of the IC (VCC) is dependent on the supply voltage of the system (VS ) and the value of the load resistor (RL). It can be calculated using the equation:
analog microelectronics
April 99 4/8
CURRENT CONVERTER IC
VCC = VS - I OUT RL
AM402
AM402 is basically made up of three function blocks (see Figure 1): 1. The amplification of the high-precision instrumentation amplifier as the input stage is adjustable and thus makes applications for a number of input signals and sensors possible. Gain GIA is set via the two external resistors R1 and R2. When selecting the resistors, the sum of R1 + R2 given in the Boundary Conditions must be heeded. When configuring the instrumentation amplifier, the user should ensure that the input signal has the correct polarity. 2. At the voltage-controlled current output an offset current can be set at the output with the help of the internal voltage reference across external resistors R3 and R4 (see the Description of Applications, beginning on page 7). Output current IOUT is provided by external transistor T1 which is driven by the output (IOUT) of the IC. One particular feature of AM402 is that the output current is switched-off if overvoltage occurs on the input side of the device. Another safety feature included in AM402 is the integrated power-down function with excessive temperature. With this, the output current is switched off if the IC gets too warm. 3. The adjustable reference voltage source supplies sensors or other external components with voltage of 5 or 10V (VSET = N.C. or VSET = GND). Additionally, any voltage value between 4.5 and 10V can be set via an external voltage divider. Please note, that Capacitor C1 (ceramic) must also be connected even when the voltage reference is not used. Initial Operation of AM402 To compensate the offset of the output current for the first time, the input must be short-circuited (VIN = 0). In doing so, it should be ensured that the input pins of the instrumentation amplifier have the voltage potentials given in the Electrical Specifications (input voltage range). The short circuit at the input produces an output current IOUT = ISET with
I SET (VIN = 0 ) = VREF R4 2R0 R3 + R4
The adjustment of the output current range depends on the choice of external resistors R1 and R2. The maximum output current is defined by the general transfer function of the IC. The following equation is given for the output current IOUT: G I OUT = V IN IA + I SET R0 The gain factor of the instrumentation amplifier G IA = 1 + R1 R2 is determined by the input voltage VIN and the maximum output current IOUTmax. The minimum supply voltage is dependent on the value of the reference voltage. The following applies: VCC VREF + 1V .
RL [] VCCmin = 6V
The choice of supply voltage VS also depends on the load resistor RL used by the application. The following inequation determines the minimum supply voltage:
VS I OUTmax RL + VCCmin .
RL
VS - VCCmin IOUTmax
RLmax = 500 IOUTmax = 20mA
500 300 Operating Area 0 0 6 12 16 24 35 VS [V]
The resulting operating range is given in Figure 4. Example calculations and typical values for the external components can be found in the example application shown in the Applications from page 7 onwards.
Figure 4
analog microelectronics
April 99 5/8
CURRENT CONVERTER IC
PINOUT
PIN NAME RS+ VCC RS- N.C. OUT N.C. SET IN- IN+ GAIN- GAIN GAIN+ VSET GND N.C. VREF
AM402
DESIGNATION Sense Resistor + Supply Voltage Sense Resistor - Not Connected Output Not Connected Set Output Current Input Negative Input Positive Gain Adjustment Gain Adjustment Gain Adjustment Reference Voltage Select IC Ground Not Connected Reference Voltage Output
RS+ VCC RS- N.C. OUT N.C. SET IN-
1 2 3 4 5 6 7 8
16 15 14 13 12 11 10 9
VREF N.C. GND VSET GAIN+ GAIN GAIN- IN+
Figure 5
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
DELIVERY
The AM402 is available in version: * 16 pin DIL packages (samples) * SO 16 (n) packages (maximum power dissipation PD = 300mW) * Dice on 5" blue foil
PACKAGE DIMENSIONS SO16 (n)
10,06 0,1 1,45 0,1 0,2 0,05 0,2 0,1 0,42 0,07 1,27 0,635 0,3 0-10 6,2 0,2 4,0 + 0,2 - 0,1
2,00
16
1
8
Figure 6
analog microelectronics
April 99 6/8
CURRENT CONVERTER IC
TYPICAL THREE-WIRE APPLICATION (0/4-20mA)
AM402
C1
R2
10 11
R1
12 13 16
VREF VS R0
1 2 3
AM 402
5/10 V reference
9
V IA I
14 7
T1 D1 R5 IOUT RL Ground
VIN
8
5
R3
R4
Figure 7 Used in a three-wire circuit, pin 2 (VCC) is connected to pin 1 (RS+) and ground pin 14 (GND) is connected to Ground (Figure 7). The Gain GIA is adjusted by external resistors R1 and R2 and can be calculated by GIA = 1 + R1 R2 R1 R2 = GIA - 1 Hence, the transfer-function of the output current IOUT becomes I OUT = VIN GIA R0 + I SET with the current ISET adjusted by external resistors R3 and R4. R3 V R4 VREF I SET = REF = -1 2 R0 R3 + R4 R4 2 R0 I SET The supply voltage must be chosen with respect to the load resistor RL described by the following equation VS IOUTmax RL +6V Example 1: Output current range 4...20mA The values of the external devices ( VIN = 0K50 mV , VREF = 5V , GIA = 8 ) are as follows R0 = 25 R1 = 33k R2 = 4.7k R3 = 100k R4 = 0...5k R5 = 40 RL = 0...500 C1 = 2.2F Example 2: Output current range 0...20mA The values of the external devices ( VIN = 0K250 mV , VREF = 5V , GIA = 2 ) are as follows R0 = 25 R1 = 22k R2 = 22k R5 = 40 R3, R4 not used (SET = GND) RL = 0...500 C1 = 2.2F
analog microelectronics
April 99 7/8
CURRENT CONVERTER IC
TYPICAL TWO-WIRE APPLICATION (4-20mA)
AM402
C1
R2
10 11
R1
12 13 16
VREF VS R0
1 2 3
AM 402
5/10 V reference
9
C2
V IA I
14 7
T1 D1 R5 IOUT
VIN
8
5
R3
R4
RL Ground
Figure 8 Used in a two-wire circuit, pin 2 (VCC) is connected to pin 3 (RS-) and ground pin 14 (GND, ) is connected to RL (Figure 8). The Gain GIA is adjusted by external resistors R1 and R2 and can be calculated by GIA = 1 + R1 R2 R1 R2 = GIA - 1 Hence, the transfer-function of the output current IOUT becomes I OUT = VIN GIA R0 + I SET with the current ISET adjusted by external resistors R3 and R4. R3 V R4 VREF I SET = REF = -1 2 R0 R3 + R4 R4 2 R0 I SET The supply voltage must be chosen with respect to the load resistor RL described by the following equation VS IOUTmax RL +6V Example 3: Output current range 4...20mA The values of the external devices ( VIN = 0K200 mV , VREF = 5V , GIA = 2 ) are as follows R0 = 25 R5 = 40 R1 = 22k RL = 0...500 R2 = 22k C1 = 2.2F R3 = 100k C2 = 100nF R4 = 0...5k
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 8/8

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