AME AM462

Industrial V/I Converter and Protector IC
AM462
PRINCIPLE FUNCTION
Conversion of input voltage referenced to ground to output current
Integrated protection for IC and external components
Integrated, adjustable current/voltage sources for external components
VCC = 6...35V
Single-ended
input voltage
AM462
0...VCC-5V
VREF = 5/10V
IOUT = e.g. 0/4...20mA
ICC = up to 10mA
TYPICAL APPLICATIONS
•
•
•
•
•
•
Adjustable voltage-to-current (V/I) converter
Adjustable voltage and current source (supply unit)
Voltage regulator with additional functions
Industrial protector and output IC for microprocessors (the Frame ASIC concept [1])
Peripheral processor IC
For examples of typical applications see Example Applications
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December2006
1/20
Rev. 2.4
Industrial V/I Converter and Protector IC
AM462
CONTENTS
CONTENTS
2
FEATURES
3
GENERAL DESCRIPTION
3
BLOCK DIAGRAM
3
ELECTRICAL SPECIFICATIONS
4
BOUNDARY CONDITIONS
6
DETAILED DESCRIPTION OF FUNCTIONS
6
INITIAL OPERATION OF AM462
6
General information on 2- and 3-wire applications and the use of current
6
Setting the output current range
6
Selecting the supply voltage
6
Using OP2 as a current source
6
Using OP2 as a voltage reference
6
POINTS TO NOTE: INITIAL OPERATION OF AM462
6
APPLICATIONS
6
Typical 3-wire application with an input signal referenced to ground
6
Typical 2-wire application with an input signal referenced to ground
6
Application for an input signal with an offset
6
BLOCK DIAGRAM AND PINOUT
6
EXAMPLE APPLICATIONS
6
DELIVERY
6
PACKAGE DIMENSIONS
6
FURTHER READING
6
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December2006
2/20
Rev. 2.4
Industrial V/I Converter and Protector IC
AM462
FEATURES
GENERAL DESCRIPTION
• Supply voltage: 6...35V
• Wide working temperature range:
–40°C...+85°C
• Adjustable integrated reference voltage
source: 4.5 to 10V
• Additional voltage/current source
• Adjustable amplification
• Adjustable offset
• Industrial current output (e.g.
0/4...20mA)
• Protection against reverse polarity
• Short-circuit protection
• Output current limitation
• Low-cost device: replaces a number of
discrete elements
• 2- and 3-wire operation
• Individually configurable function
modules
• RoHS compilant
AM462 is a universal V/I converter and
amplifier IC with a number of additional
functions. The IC basically consists of an
amplifier, whose gain can be set externally,
and an output stage which can convert voltage
signals referenced to ground to industrial
current signals. An additional reference
voltage source for the supply of external
components is also included in the device. A
further operational amplifier can be connected
up as a current source, voltage reference or
comparator.
One of the main features of the IC is its
integrated protective circuitry. The device is
protected against reverse polarity and has a
built-in output current limit. Converter IC
AM462 enables industrial current loop signals
(e.g. of 0/4–20mA) to be produced relatively
easily.
Using the Frame ASIC concept [1] the IC can
be connected up to a processor for signal
correction.
BLOCK DIAGRAM
VSET VREF
SET
16
15
13
CVREF
AM462
CVSET
1
I
2
OP2
11
10
Voltage Reference
9
VBG
V
INP
8
3
RS+
VCC
RSIOUT
OP1
4
INN
5
OUTAD
6
GND
INDAI
14
Figure 1: Block diagram of AM462 (individually configurable function modules)
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December2006
3/20
Rev. 2.4
Industrial V/I Converter and Protector IC
AM462
ELECTRICAL SPECIFICATIONS
Tamb = 25°C, VCC = 24V, VREF = 5V, IREF = 1mA (unless otherwise stated); currents flowing into the IC are negative.
Parameter
Symbol
Supply 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
DIL16 plastic package
70
°C/W
Θja
SO16 narrow plastic package
140
°C/W
VREF
VSET not connected
4.75
5.00
5.25
V
VREF10
VSET = GND, VCC ≥ 11V
9.5
10.0
10.5
V
125
°C
150
°C
Voltage Reference
Voltage
Trim Range
VREFADJ
Current
IREF*
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
VREF10
V
0
10.0
mA
±90
±140
ppm/°C
30
80
ppm/V
60
150
ppm/V
dVREF/dI
0.05
0.10
%/mA
0.06
0.15
%/mA
1.9
2.2
5.0
µF
1.20
1.27
1.35
V
±60
±140
ppm/°C
0
10
mA
IREF ≈ 5mA
dVREF/dI
Load Capacitance
4.5
CL
Current/Voltage Source OP2
Internal Reference
VBG
VBG vs. Temperature
dVBG/dT
Tamb = – 40...+85°C
Current Source: ICV = VBG/RSET, from Figure
5
Adjustable Current Range
ICV*
Output Voltage
VCV
VCC < 19V
VBG
VCC – 4
V
VCV
VCC ≥ 19V
VBG
15
V
Voltage Source: VCV = VBG (1 + R7 / R6), from Figure
Adjustable Voltage Range
Output Current
Load Capacitance
6
VCV
VCC < 19V
0.4
VCC – 4
V
VCV
VCC ≥ 19V
0.4
15
V
ICV*
Source
ICV
Sink
CL
Source mode
0
1
10
mA
–100
µA
10
nF
Operational Amplifier Gain Stage (OP1)
Adjustable Gain
GGAIN
Input Range
IR
VCC < 10V
0
VCC – 5
V
IR
VCC ≥ 10V
0
5
V
±2
mV
Power Supply Rejection Ratio
PSRR
Offset Voltage
VOS
1
80
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90
±0.5
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dB
December2006
4/20
Rev. 2.4
Industrial V/I Converter and Protector IC
AM462
Parameter
Symbol
Conditions
Min.
Typ.
Max.
Unit
µV/°C
Operational Amplifier Gain Stage (OP1) (cont.)
VOS vs. Temperature
dVOS/dT
±3
±7
Input Bias Current
IB
10
25
nA
IB vs. Temperature
dIB/dT
7
20
pA/°C
Output Voltage Limitation
VLIM
Output Voltage Range
VOUTAD
VCC < 10V
0
VCC – 5
V
VOUTAD
VCC ≥ 10V
0
VREF
V
250
pF
Load Capacitance
VREF
CL
V
V/I Converter
Internal Gain
GVI
Trim Range
Adjustable by R0
0,12
0.125
0,13
0.75
1.00
1.25
Voltage Range at R0 FS
VR0FS
750
mV
Offset Voltage
VOS
F
≥ 100
350
±2
±4
mV
VOS vs. Temperature
dVOS/dT
F
≥ 100
±7
±14
µV/°C
Input Resistance
RIN
120
160
RIN vs. Temperature
dRIN/dT
0.2
0.3
Output Offset Current
IOUTOS
3-wire operation
–25
–35
µA
IOUTOS vs. Temperature
dIOUTOS/dT
3-wire operation
16
26
nA/°C
Output Offset Current
IOUTOS
2-wire operation
9.5
14
µA
IOUTOS vs. Temperature
dIOUTOS/dT
2-wire operation
6
8
nA/°C
Output Control Current
IOUTC
2-wire operation, VR0/100mV
6
8
µA
IOUTC vs. Temperature
dIOUTC/dT
2-wire operation
–15
nA/°C
Output Voltage Range
VOUT
VOUT = 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
Output Resistance
ROUT
Load Capacitance
CL
–10
0.5
kΩ
kΩ/°C
20
mA
1.0
MΩ
0
500
nF
SET Stage
Internal Gain
GSET
Input Voltage
VSET
0.5
1.15
V
Offset Voltage
VOS
±0.5
±1.5
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
635
0
Protection Functions
Voltage Limitation at R0
VLIMR0
Protection against reverse polarity
Current in the event of reverse polarity
VINDAI = 0, VR0 = GSET VSET
690
mV
Ground vs. VS vs. VOUT
580
35
V
Ground vs. VS vs. IOUT
35
V
Ground = 35V, VS = IOUT = 0
4.5
Ideal input
0.05
mA
System Parameters
Nonlinearity
0.15
%FS
* In 2-wire operation a maximum current of IOUTmin – ICC is valid
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December2006
5/20
Rev. 2.4
Industrial V/I Converter and Protector IC
AM462
BOUNDARY CONDITIONS
Parameter
Symbol
Conditions
Sense Resistor
R0
IOUTFS = 20mA
R
c = 20mA/IOUTFS
Stabilization Resistor
R
IOUTFS = 20mA
R
c = 20mA/IOUTFS
RL
Limitation only for 3-wire operation
Load Resistance
Sum Gain Resistors
R1 + R2
Sum Offset Resistors
R3 + R4
Min.
Typ.
Max.
17
27
38
c ⋅ 17
c ⋅ 27
c ⋅ 38
35
40
45
c ⋅ 35
c ⋅ 40
c ⋅ 45
Unit
0
600
20
200
k
200
k
VREF Capacitance
C1
Ceramic
1.9
2.2
5.0
µF
Output Capacitance
C2
Only for 2-wire operation
90
100
250
nF
D1 Breakdown Voltage
VBR
T1 Forward Current Gain
F
20
BCX54/55/56, for example
35
50
50
150
V
DETAILED DESCRIPTION OF FUNCTIONS
AM462 is a modular, universal V/I converter and protector IC which has been specially developed
for the conditioning of voltage signals referenced to ground. It is designed for both 2- and 3-wire
operation in industrial applications (cf. application in Figure 8). AM462’s various functions are
depicted in the block diagram (Figure 2) which also illustrates how few external components are
required for the operation of this particular device.
AM462 consists of several modular function blocks (operational amplifiers, voltage-to-current
converters and references) which, depending on external configurations, can either be switched to
one another or operated separately (see the basic circuitry in Figure 2):
1. Operational amplifier stage OP1 enables a positive voltage signal to be amplified. OP1 gain
GGAIN can be set via external resistors R1 and R2. Protective circuitry against overvoltage is
integrated into the chip, limiting the voltage to the set value of the reference voltage. Output
voltage VOUTAD at pin OUTAD is calculated as:
VOUTAD = VINP ⋅ GGAIN with GGAIN = 1 +
R1
R2
(1)
where VINP is the voltage at OP1’s input pin INP.
2. The internal voltage-to-current converter (V/I converter) provides a voltage-controlled current
signal at IC output IOUT (pin 8) which activates an external transistor T1; this in turn supplies
the actual output current IOUT. To reduce power dissipation the transistor is an external
component and protected against reverse polarity by an additional diode D1. Via pin SET an
offset current ISET can be set at output IOUT (with the help of the internal voltage reference and
an external voltage divider as shown in Figure 2, for example). External resistor R0 permits the
output current to be finely adjusted with parallel operation of current and the voltage output. For
the output current provided by T1 the following ratio applies:
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December2006
6/20
Rev. 2.4
Industrial V/I Converter and Protector IC
AM462
I OUT =
VINDAI
V
+ I SET with I SET = SET
8 R0
2R 0
(2)
with VINDAI the voltage at pin INDAI and VSET the voltage at pin SET (V/I converter inputs)1.
VREF
VCVREF
1
AM462
VCVSET
C1
R3
15
13
R4
16
VS
VSET
I
2
OP2
11
R0
10
Voltage Reference
9
VBG
V
VINP
8
T1
D1
3
OP1
5
4
R2
6
R1
VOUTAD
14
R5
IOUT
VINDAI
Ground
Figure 2: Block diagram of AM462 with external components (3-wire circuit for current output)
3. The AM462 reference voltage source enables voltage to be supplied to external components
(such as sensors, microprocessors, etc.). The reference voltage value VREF can be set via pin 13
VSET. If pin VSET is not connected, VREF = 5V; if VSET is switched to ground, VREF = 10V.
Values between the above can be set if two external resistors are used (inserted between pin
VREF and pin VSET and between pin VSET and GND; see Figure 2).
External (ceramic) capacitor C1 at pin VREF stabilizes the reference voltage. It must be
connected even if the voltage reference is not in use.
4. The additional operational amplifier stage OP2 can be used as a current or voltage source to
supply external components. OP2's positive input is connected internally to voltage VBG so that
the output current or output voltage can be set across a wide range using one or two external
resistors.
1
The construction of the V/I converter is such that output current IOUT is largely independent of the current
amplification βF of external transistor T1. Production-specific variations in the current amplification of the transistors
used are compensated for internally by the V/I converter.
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December2006
7/20
Rev. 2.4
Industrial V/I Converter and Protector IC
AM462
INITIAL OPERATION OF AM462
General information on 2- and 3-wire applications and the use of current
In 3-wire operation (cf. Figure 3 right and Figure 7) the ground of the IC (pin GND) is connected up
to the external mass of the system Ground. The system's supply voltage VS is connected to pin VCC
and pin VCC to pin RS+.
In 2-wire operation (cf. Figure 3 left and Figure 7) system supply voltage VS is connected to pin
RS+ and pin VCC to RS-. The ground of the IC (pin GND) is connected to the node between resistor
R5 and load resistor RL (current output IOUT). IC ground (GND) is not the same as system ground
(Ground)!! The output signal is picked up via load resistor RL which connects current output IOUT to
the system ground.
In 2-wire operation the IC ground is "virtual" (floating), as with a constant load resistance the
supply voltage of the device VCC changes according to the current. As a rule, the following equation
applies to 2-wire operation:
VCC = VS − I OUT (VIN ) RL
(2)
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 3-wire operation VCC = VS, as the IC ground is connected to the ground of the system.
2-wire system
signal source and
conditioning IC
GND ≠ Ground
VCC ≠ VS
3-wire system
signal source and
conditioning IC
VCC
IOUT
GND
RL
VS
GND = Ground
VCC = VS
Ground
IOUT
RL
VCC = VS
Ground = GND
Figure 3: The difference between 2- and 3-wire operation
Setting the output current range
When using amplification stage OP1 together with the V/I converter for voltage-to-current
conversion the offset of the output current should first be compensated for by suitable selection of
resistors R3 and R4. To this end the OP1 input must be connected to ground (VINP = 0). With the
short circuit at the input and by connecting up V/I converter pin VSET as shown in Figure 2 the
values of the output current according to Equation 2 are as follows:
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December2006
8/20
Rev. 2.4
Industrial V/I Converter and Protector IC
AM462
I OUT (V INDAI = 0 ) = I SET =
V REF
R4
⋅
2 R 0 R3 + R 4
(3)
and thus for the ratio of the resistors R3/R4:
R3
VREF
=
−1
R4 2R0 I SET
(4)
The output current range is set in conjunction with the selected external resistors R1 and R2 (or fine
adjustment with R0 ). Using Equations 1 and 2 the following is calculated for output current IOUT :
I OUT = VINP
GGAIN
R
+ I SET with GGAIN = 1 + 1
8 R0
R2
(5)
Selecting the supply voltage
System supply voltage VS needed to operate AM462 is dependent on the selected mode of
operation.
When using current output pin IOUT (in conjunction with the external transistor) the value of VS is
dependent on that of the relevant load resistor RL (max. 600Ω) used by the application. The
minimum system supply voltage VS is then:
VS ≥ I OUT max RL + VCC min
(6)
Here, IOUTmax stands for the maximum output current and VCCmin for the minimum IC supply voltage
which is dependent on the selected reference voltage:
VCC min ≥ VREF + 1V
RL [Ω]
RL
(7)
VCCmin = 6V
VS − VCCmin
IOUTmax
RLmax = 600Ω
IOUTmax = 20mA
600
300
Working range
0
0
6
12
24
18
35
VS [V]
Figure 4: Working range in conjunction with the load resistor
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December2006
9/20
Rev. 2.4
Industrial V/I Converter and Protector IC
AM462
The working range resulting from Equation 6 is described in Figure 4. Example calculations and
typical values for the external components can be found in the example applications from page 13
onwards.
Using OP2 as a current source
The additional operational amplifier OP2 can easily be connected up as a constant current source.
Using the circuit in Figure 5 the following applies:
OP2 connected as
current source
IS
AM462
1
2
OP2
RSET
VBG
Figure 5: Using OP2 as a constant current source
Example : OP2 as courrent source
IS =
V BG
1 .27 V
=
R SET
R SET
(8)
The bridge symbol represents the component to be supplied with current (e.g. a piezoresistive
sensing element or temperature sensor).
A supply current of IS = 1mA is to be set. Using Equation 8 the following value is calculated for
external resistor RSET, which in turn stipulates the size of the current:
R SET =
V BG
1 .27 V
=
= 1 .27 k Ω
IS
1mA
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Rev. 2.4
Industrial V/I Converter and Protector IC
AM462
Using OP2 as a voltage reference
In addition to the integrated voltage reference OP2 can also be used to supply voltage to external
components, such as A/D converters and microprocessors, for example. Lower voltages can be
generated (e.g. 3.3V) which with the increasing miniaturization of devices and need for ever lower
levels of power dissipation in digital components is today of growing importance.
OP2 connected as
voltage reference
VCVREF
µP
AM462
R6
1
2
OP2
R7
VBG
Figure 6: Using OP2 as a voltage reference
The additional operational amplifier OP2 can easily be connected up as a voltage reference. Using
the circuit in Figure 6 the following applies:

R 
V CVREF = V BG  1 + 6  = 1 . 27 V
R7 


R 
 1 + 6 
R7 

(9)
Example : OP2 as voltage reference
A voltage of VCVREF = 3.3V is to be set. Using Equation 9 the following ratio is calculated for
external resistors R6 and R7:
R 6 V CVREF
=
− 1 ≈ 2 , 6 − 1 = 1,6
R7
V BG
The following example values are produced for the resistors:
R7 = 10kΩ
R6 = 16kΩ
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December2006
11/20
Rev. 2.4
Industrial V/I Converter and Protector IC
AM462
POINTS TO NOTE: INITIAL OPERATION OF AM462
1. When operating AM462 it is imperative that external capacitor C1 is always connected (cf.
Figure 2). Care must be taken that the value of the capacitance does not lie beyond its given
range, even across the range of temperature (see Boundary Conditions on page 7). In 2-wire
operation ceramic capacitor C2 must also be used (cf. Figure 8).
2. In a 2-wire setup the power consumption of the overall system (AM462 plus all external
components, including the configuration resistors) must not exceed the sum of IOUTmin (usually
4mA).
3. All AM462 function blocks not required by the application must be connected to a defined (and
allowed) potential.
4. A load resistance of 600Ω maximum is permitted for the current output.
5. The values of external resistors R0, R1, R2, R3, R4 and R5 must be selected within the permissible
range given in the boundary conditions on page 7.
APPLICATIONS
Typical 3-wire application with an input signal referenced to ground
Figure 7 shows a 3-wire application in which AM462 amplifies and converts a positive voltage
signal referenced to ground. The unused blocks (e.g. OP2) have been set to defined operating points
in the application. Alternatively, these function groups can also be used here (e.g. to supply external
components).
For output current IOUT the following applies according to Equations 1 and 2:
I OUT = VINP ⋅
R
GI
+ I SET with GI = GGAIN = 1 + 1
8 R0
R2
Example: 0…20mA Voltage-To-Current Transmitter
To obtain a signal of VINP = 0...1V at the OP1 input the external components are to be dimensioned
in such a way that the output current has a range of 0...20mA (i.e. ISET = 0 ⇒ SET = GND). With
R0 = 27Ω:
I OUT = VINP ⋅
G
GI
+ I SET = VINP ⋅ GAIN
8R0
8 R0
The following then applies to the gain:
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December2006
12/20
Rev. 2.4
Industrial V/I Converter and Protector IC
AM462
3-wire connection
C1
1
AM462
16
15
13
VS
ISET = 0
I
2
OP2
11
R0
10
Voltage Reference
9
VBG
V
VINP
8
T1
D1
3
OP1
6
5
4
Single-ended
input voltage
14
R5
R1
R2
IOUT
RL
Ground
Connections setting unused function blocks to a defined operating point
Figure 7: Typical application for input signals referenced to ground
GGAIN = 8R0
I OUT
20mA
= 8 ⋅ 27Ω ⋅
≈ 4.32 ⇒
VINP
1V
R1
= 4.32 − 1 = 3.32
R2
Observing the boundary conditions (page 7), the following values are obtained for the external
components:
R1 ≈ 33.2kΩ R2 = 10kΩ
R0 = 27Ω
R5 = 39Ω
RL = 0...600Ω
C1 = 2.2µF
Typical 2-wire application with an input signal referenced to ground
In 2-wire operation (cf. Figure 8) system supply voltage VS is connected up to pin RS+ and pin VCC
to pin RS-. The ground of the IC (pin GND) is connected to the node between resistor R5 and load
resistor RL.. IC ground (GND) is not the same as system ground (Ground). The output signal is
picked up via load resistor RL which connects current output IOUT to the system ground.
It must be ensured that in 2-wire operation an additional current load (use of current/voltage source)
is limited to 4mA due to the domestic current supply and limitation.
For output current IOUT the following applies according to Equations 1 and 2:
I OUT = VINP ⋅
R
GI
V
R4
+ I SET with GI = GGAIN = 1 + 1 and I SET = REF ⋅
8R0
R2
2R0 R3 + R4
analog microelectronics
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Internet: http://www.analogmicro.de
Phone:
Fax:
Email:
+49 (0)6131/91 073 - 0
+49 (0)6131/91 073 – 30
info@analogmicro.de
December2006
13/20
Rev. 2.4
Industrial V/I Converter and Protector IC
AM462
C1
1
AM462
R3
VS
16
15
13
R4
2
OP2
C2
R0
11
I
10
Voltage Reference
9
VBG
V
VINP
8
T1
D1
3
OP1
2-wire
connection
6
5
4
Single-ended
input voltage
R2
R1
IC ground: GND
14
}
System ground: Ground
different
potentials!
R5
IOUT
RL
GND
Ground
Connections setting unused function blocks to a defined operating point
Figure 8: Typical 2-wire operation for input signals referenced to ground
Example : 4…20mA Voltage-To-Current Transmitter
To obtain a signal of VINP = 0...1V at the OP1 input the external components are to be dimensioned
in such a way that the output current has a range of 4...20mA. The following applies:
I OUT = VINP ⋅
G
GI
+ I SET = VINP ⋅ GAIN + 4mA
8 R0
8R0
With R0 = 27Ω and ISET = 4mA Equation 4 produces the following for resistors R3 and R4:
R3
VREF
5V
=
−1 =
− 1 ≈ 22.15
2 ⋅27Ω ⋅ 4mA
R4 2R0 I SET
and thus the following value for the gain:
GGAIN = 8R0
I OUT max − I SET
16mA
= 8 ⋅ 27Ω ⋅
= 3.456
1V
VINP
⇒
R1
= 3.456 − 1 = 2.456
R2
Observing the given boundary conditions, the following values are obtained for the external
components:
R1 ≈ 24.56kΩ
R0 = 27Ω
R2 = 10kΩ
R5 = 39Ω
R3 ≈ 44.3kΩ
RL = 0...600Ω
R4 = 2kΩ
C1 = 2.2µF
analog microelectronics
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Internet: http://www.analogmicro.de
Phone:
Fax:
Email:
+49 (0)6131/91 073 - 0
+49 (0)6131/91 073 – 30
info@analogmicro.de
C2 = 100nF
December2006
14/20
Rev. 2.4
Industrial V/I Converter and Protector IC
AM462
Application for an input signal with an offset
It is not uncommon for input signals to have an offset (e.g. of 0.5...4.5V or 1...6V). For signals such
as these an offset current is generated at the IC output also when ISET = 0. The circuit can then be
dimensioned as described in the following.
According to Equation 2 the following applies for a required current swing at the output of
∆IOUT = IOUTmax – IOUTmin:
∆I OUT =
∆VPIN 6
8R0
⇒ ∆VPIN 6 = 8R0 ∆I OUT
(10)
For an input current swing of ∆VIN = VINmax – VINmin the necessary gain is calculated as:
G=
∆VPIN 6
∆VIN
(11)
If G < 1, the input signal can be routed directly to pin 6 (INDAI) via a voltage divider without OP1
having to be used (see Figure 9). With this circuitry the following results:
G=
∆VPIN 6
R9
=
∆VIN
R8 + R9
⇒
∆VIN
R8
=
−1
R9 ∆VPIN 6
(12)
From input offset VINmin the following output current is then obtained when ISET = 0:
I OUT (VIN min ) = VIN min ⋅
R9
1
⋅
R8 + R9 8R0
(13)
Using the SET pin and Equation 2 the required minimum output current IOUTmin can then be set:
I OUT = VIN ⋅
R9
1
V
R4
⋅
+ I SET with I SET = REF ⋅
2R0 R3 + R4
R8 + R9 8 R0
(14)
Example : 4..20mA Voltage-To-Current Transmitter with Input Signal Offset
To obtain a signal of VIN = 0.5...4.5V the external components are to be dimensioned in such a way
that the output current has a range of 4...20mA. The circuitry is shown in Figure 9. OP1 is not used
here. It is, however, available to the user as an additional OP and can be used as an impedance
converter at the voltage-to-current converter input INDAI, for example.
With reference to Equation 10 and with R0 = 27Ω, a voltage swing is obtained at pin 6 of:
∆VPIN 6 = 8R0 ∆I OUT = 8 ⋅ 27Ω ⋅16mA = 3.456V
Using Equation 12 the following applies:
R8 ∆VIN − ∆VPIN 6 4V − 3.456V
=
=
≈ 0.157
∆VPIN 6
3.456V
R9
⇒
R9 = 6.35 ⋅R8
analog microelectronics
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Internet: http://www.analogmicro.de
Phone:
Fax:
Email:
+49 (0)6131/91 073 - 0
+49 (0)6131/91 073 – 30
info@analogmicro.de
December2006
15/20
Rev. 2.4
Industrial V/I Converter and Protector IC
AM462
C1
1
AM462
R3
VS
16
15
13
3-wire connection
R4
I
2
OP2
11
R0
10
Voltage reference
9
VBG
V
8
T1
D1
3
OP1
6
5
4
14
R5
R8
V IN
Single-ended
input voltage
R9
IOUT
RL
Connections setting unused function blocks in a defined operating point
Ground
Figure 9: Converting an input signal with an
According to Equation 13 the minimum output current generated by the input offset is calculated
as:
I OUT min = VIN min ⋅
R9
1
6,37
1
⋅
= 0.5V ⋅
⋅
≈ 2mA
R8 + R9 8R0
6.37 + 1 8 ⋅ 27Ω
To obtain an output current of IOUT = 4...20mA, according to the above a current of ISET = 2mA must
then be added. With reference to Equation 4 the ratio of R3 to R4 is calculated thus:
!
I SET = 2mA =
VREF
R4
⋅
2R0 R3 + R4
⇒
R3
VREF
5V
=
−1 =
− 1 ≈ 45.3
2 ⋅ 27Ω ⋅ 2mA
R4 2R0 I SET
Observing the given boundary conditions, the following values are obtained for the external
components:
R0 ≈= 27Ω
R5 = 39Ω
R8 ≈ 10kΩ
RL = 0...600Ω
R9 = 63.7kΩ
C1 = 2.2µF
R3 = 90.6kΩ
analog microelectronics
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Internet: http://www.analogmicro.de
Phone:
Fax:
Email:
+49 (0)6131/91 073 - 0
+49 (0)6131/91 073 – 30
info@analogmicro.de
R4 = 2kΩ
December2006
16/20
Rev. 2.4
Industrial V/I Converter and Protector IC
AM462
BLOCK DIAGRAM AND PINOUT
VSET VREF
SET
16
15
13
CVREF
1
AM462
CVSET
I
2
OP2
11
10
Voltage Reference
9
VBG
V
INP
8
3
RS+
VCC
RSIOUT
OP1
5
4
INN
6
OUTAD
GND
INDAI
14
Figure 10: Block diagram of AM462
PIN
NAME
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
CVREF
CVSET
INP
INN
OUTAD
INDAI
N.C.
IOUT
RS–
VCC
RS+
N.C.
VSET
GND
VREF
SET
EXPLANATION
Current/Voltage reference
Current/Voltage reference set
Positive input
Negative input
System amplification output
Current output stage input
Not connected
Current output
Sensing resistor Supply voltage
Sensing resistor +
Not connected
Reference voltage source set
IC ground
Reference voltage source output
Output offset current set
CVREF
CVSET
INP
INN
OUTAD
INDAI
N.C.
IOUT
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
SET
VREF
GND
VSET
N.C.
RS+
VCC
RS-
Figure 11: AM462 Pin out
Table 1: AM462 Pin out
analog microelectronics
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Internet: http://www.analogmicro.de
Phone:
Fax:
Email:
+49 (0)6131/91 073 - 0
+49 (0)6131/91 073 – 30
info@analogmicro.de
December2006
17/20
Rev. 2.4
Industrial V/I Converter and Protector IC
AM462
EXAMPLE APPLICATIONS
•
Application as a voltage-to-current converter IC
6...35V
VIN = 0...1, 0...5V
... and other
Protection against
short circuiting and
reverse polarity
0/4...20mA
AM462
Figure 12: Application as a current converter IC
•
Converting a 0.5...4.5V sensor (voltage) signal
6...35V
VREF = 5/10V
Sensor
VOUT = 0.5...4.5V
AM462
Protection against
short circuiting
and reverse polarity
4...20mA
Figure 13: Converting a 0.5...4.5V sensor signal
•
Configuration as a peripheral processor IC [2]
VCVR EF = 3.3V
µP
6...35V
VREF = 5V
DAC
AM462
Protection against
short circuiting and
reverse polarity
0/4...20mA
Figure 14: Configuration as a peripheral processor IC and supply unit
analog microelectronics
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Internet: http://www.analogmicro.de
Phone:
Fax:
Email:
+49 (0)6131/91 073 - 0
+49 (0)6131/91 073 – 30
info@analogmicro.de
December2006
18/20
Rev. 2.4
Industrial V/I Converter and Protector IC
AM462
•
Application as an analog output IC and supply unit for sensors
VR EF = 5/10V
6...35V
VCV REF = 3.3V
Sensor
µP
DAC
AM462
Protection against
short circuiting and
reverse polarity
0/4...20mA
Figure 15: Output IC and supply unit in sensor applications
•
Application as a front-end and back-end IC for microprocessors
VCVREF=3.3V
6...35V
VREF=5/10V
Sensor
AM462
Protection against
short circuiting and
reverse polarity
0/4...20mA
ADC DAC
µP
Figure 16: Application as an analog front end and back end for microprocessors
(Frame ASIC concept)
analog microelectronics
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Internet: http://www.analogmicro.de
Phone:
Fax:
Email:
+49 (0)6131/91 073 - 0
+49 (0)6131/91 073 – 30
info@analogmicro.de
December2006
19/20
Rev. 2.4
Industrial V/I Converter and Protector IC
AM462
DELIVERY
The AM462 V/I converter and protector IC is available as the following packages:
• SSOP16
• SO16(n)
• Dice on 5" blue foil (on request)
PACKAGE DIMENSIONS
Please see our website (data sheets: package.pdf).
FURTHER READING
www.analogmicro.de
[1]
The Frame ASIC concept: See:
[2]
The AM462 can be used as an integrated solution to interface a microprocessor to the industrial
4...20mA network. See: Technical Articles: PR1011 and
Interfacing the µProcessor with the 4...20mA current loop signal (PLC). See: Application notes
AN1014.
NOTES
Analog Microelectronics reserves the right to make amendments to any dimensions, technical data or other information contained herein without further
notice.
analog microelectronics
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Internet: http://www.analogmicro.de
Phone:
Fax:
Email:
+49 (0)6131/91 073 - 0
+49 (0)6131/91 073 – 30
info@analogmicro.de
December2006
20/20
Rev. 2.4