AME AM402

CURRENT CONVERTER IC
AM402
FEATURES
GENERAL DESCRIPTION
• Wide Supply Voltage Range: 6...35V
• Wide Operating Temperature Range:
–40°C...+85°C
• 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 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
9
1
V
Instrumentation
Amplifier
IN+
2
3
8
I
IN−
14
GND
RS+
VCC
RS−
5
OUT
7
SET
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: info@analogmicro.de
April 99
1/8
Rev. 2.1
CURRENT CONVERTER IC
AM402
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
°C
Temperature Specifications
Operating
Tamb
–40
85
Storage
Tst
–55
125
°C
Junction
TJ
150
°C
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
VREF
VSET = GND, VCC ≥ 11V
9.5
10.0
10.5
V
Voltage Reference
Voltage
Trim Range
VR10
4.5
VR10
V
Current
IREF*
0
10
mA
VREF vs. Temperature
dVREF/dT
±140
ppm/°C
Line Regulation
Load Regulation
±90
dVREF/dV
VCC = 6V...35V
30
80
ppm/V
dVREF/dV
VCC = 6V...35V, IREF ≈ 5mA
60
150
ppm/V
dVREF/dI
dVREF/dI
Load Capacitance
Tamb = – 40...+85°C
IREF ≈ 5mA
CL
1.9
0.05
0.10
%/mA
0.06
0.15
%/mA
2.2
5.0
µF
1.15
V
SET Stage
Internal Gain
GSET
Input Voltage
VSET
0.5
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
0
580/GIA
mV
0
Instrumentation Amplifier
Adjustable Gain
GIA
Differential Input Voltage Range
VIN
Common Mode Input Range
1
SET = GND
5
CMIR
VCC < 9V
1.5
VCC – 3
V
CMIR
VCC ≥ 9V
1.5
6.0
V
Common Mode Rejection Ratio
CMRR
80
90
Power Supply Rejection Ratio
PSRR
80
90
dB
Offset Voltage
VOS
±1
VOS vs. Temperature
dVOS/dT
±5
Input Bias Current
IB
8
20
nA
6
15
pA/°C
dB
±3
mV
µV/°C
IB vs. Temperature
dIB/dT
Input Offset Current
IOS
0.2
nA
IOS vs. Temperature
dIOS/dT
0.8
pA/°C
Output Voltage Range FS
VOUTFS
Load Capacitance
CL
VOUTFS = VGAIN+ – VGAIN–
analog microelectronics
400
500
580
mV
250
pF
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CURRENT CONVERTER IC
Parameter
Symbol
Conditions
AM402
Min.
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
700
mV
Protection Functions
Voltage Limitation at R0
Temperature Limitation
VLIMR0
VR0 = VIN GIA, SET = GND
VLIMR0
VIN = 0, VR0 = VSET/2
TLIMIT
580
640
580
635
690
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
Symbol
Conditions
R0
IOUTFS = 20mA
R0
c = 20mA/IOUTFS
R5
IOUTFS = 20mA
R5
c = 20mA/IOUTFS
RL
limitation only for 3–wire operation
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
25
50
kΩ
200
kΩ
5.0
µF
250
nF
Sum Gain Resistors
R1 + R2
Sum Offset Resistors
R3 + R4
20
C1
1.9
2.2
VREF Capacitance
Output Capacitance
C2
90
100
D1 Breakdown Voltage
VBR
only for 2–wire operation
35
50
T1 Forward Current Gain
βF
50
150
analog microelectronics
V
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CURRENT CONVERTER IC
AM402
FUNCTIONAL DIAGRAMS
Reference Voltage
3−Wire System
VS
RA
V
VIN
RIN
IA
IOUT
I
RB
RL
Ground
Figure 2
Reference Voltage
2−Wire System
VS
RA
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:
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CURRENT CONVERTER IC
AM402
VCC = VS − I OUT ⋅ RL
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 .
VCCmin = 6V
RL [Ω]
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 .
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.
RL ≤
VS − VCCmin
IOUTmax
RLmax = 500Ω
IOUTmax = 20mA
500
300
Operating Area
0
0
6
12
16
24
35
VS [V]
Figure 4
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CURRENT CONVERTER IC
AM402
PINOUT
RS+
1
16
VREF
VCC
2
15
N.C.
RS−
3
14
GND
N.C.
4
13
VSET
OUT
5
12
GAIN+
N.C.
6
11
GAIN
SET
7
10
GAIN−
IN−
8
9
IN+
Figure 5
PIN
NAME
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
RS+
VCC
RS–
N.C.
OUT
N.C.
SET
IN–
IN+
GAIN–
GAIN
GAIN+
VSET
GND
N.C.
VREF
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
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
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
16
1
8
Figure 6
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CURRENT CONVERTER IC
AM402
TYPICAL THREE–WIRE APPLICATION (0/4–20mA)
C1
R2
R1
11
10
VREF
12
13
VS
16
AM 402
R0
5/10 V reference
9
VIN
1
V
T1
2
IA
3
8
I
14
5
D1
R5
IOUT
7
R3
RL
R4
Ground
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 = 25Ω
R1 = 33kΩ
R2 = 4.7kΩ
R3 = 100kΩ
R4 = 0...5kΩ
R5 = 40Ω
RL = 0...500Ω
C1 = 2.2µF
Example 2: Output current range 0...20mA
The values of the external devices ( VIN = 0K250 mV , VREF = 5V , GIA = 2 ) are as follows
R0 = 25Ω
R1 = 22kΩ
R2 = 22kΩ
R5 = 40Ω
R3, R4 not used (SET = GND)
RL = 0...500Ω
C1 = 2.2µF
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CURRENT CONVERTER IC
AM402
TYPICAL TWO–WIRE APPLICATION (4–20mA)
C1
R2
R1
11
10
VREF
12
13
VS
16
AM 402
R0
5/10 V reference
9
VIN
1
V
C2
T1
2
IA
3
8
I
14
5
D1
R5
IOUT
7
R3
RL
R4
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 = 25Ω
R5 = 40Ω
R1 = 22kΩ
RL = 0...500Ω
R2 = 22kΩ
C1 = 2.2µF
R3 = 100kΩ
C2 = 100nF
R4 = 0...5kΩ
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
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