CURRENT CONVERTER IC
FEATURES
•
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 Instru-
mentation 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 Tempera-
ture
AM402
GENERAL DESCRIPTION
AM402 is a monolithically integrated current
converter which has been specially developed
for the processing of differential bridge sig-
nals. AM402 is suitable for two- and three-
wire applications and has four function blocks.
A high-precision instrumentation amplifier
(IA) serves as an input stage. A reference volt-
age source, which can be adjusted to values of
between 4.5 and 10V, excites external compo-
nents and a voltage-controlled current output
stage converts the voltage signal. It is thus
possible to generate output currents which cor-
respond 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
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
ELECTRICAL SPECIFICATIONS
T
amb
= 25°C,
V
CC
= 24V,
V
REF
= 5V,
I
REF
= 1mA (unless otherwise noted)
Parameter
Voltage Range
Quiescent Current
Temperature Specifications
Operating
Storage
Junction
Thermal Resistance
T
amb
T
st
T
J
Θ
ja
Θ
ja
Voltage Reference
Voltage
V
REF
V
REF
Trim Range
Current
V
REF
vs. Temperature
Line Regulation
V
R10
I
REF
*
dV
REF
/dT
dV
REF
/dV
dV
REF
/dV
Load Regulation
dV
REF
/dI
dV
REF
/dI
Load Capacitance
SET Stage
Internal Gain
Input Voltage
Offset Voltage
V
OS
vs. Temperature
Input Bias Current
I
B
vs. Temperature
Instrumentation Amplifier
Adjustable Gain
Differential Input Voltage Range
Common Mode Input Range
G
IA
V
IN
CMIR
CMIR
Common Mode Rejection Ratio
Power Supply Rejection Ratio
Offset Voltage
V
OS
vs. Temperature
Input Bias Current
I
B
vs. Temperature
Input Offset Current
I
OS
vs. Temperature
Output Voltage Range FS
Load Capacitance
CMRR
PSRR
V
OS
dV
OS
/dT
I
B
dI
B
/dT
I
OS
dI
OS
/dT
V
OUT
FS
C
L
V
OUT
FS
=
V
GAIN+
–
V
GAIN–
400
SET
=
GND
V
CC
< 9V
V
CC
≥
9V
1
0
1.5
1.5
80
80
90
90
±1
±5
8
6
0.2
0.8
500
5
G
SET
V
SET
V
OS
dV
OS
/dT
I
B
dI
B
/dT
0
±0.5
±1.6
8
7
0.5
C
L
I
REF
≈
5mA
1.9
T
amb
= – 40...+85°C
V
CC
= 6V...35V
V
CC
= 6V...35V,
I
REF
≈
5mA
VSET
not connected
VSET
=
GND, V
CC
≥
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
V
CC
I
CC
T
amb
= – 40...+85°C,
I
REF
= 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
V
R10
10
±140
80
150
0.10
0.15
5.0
V
V
V
mA
ppm/°C
ppm/V
ppm/V
%/mA
%/mA
µF
1.15
±2.5
±5
20
18
V
mV
µV/°C
nA
pA/°C
580/G
IA
V
CC
– 3
6.0
mV
V
V
dB
dB
mV
µV/°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
R
0
FS
Offset Voltage
V
OS
vs. Temperature
Output Offset Current
I
OUTOS
vs. Temperature
Output Offset Current
I
OUTOS
vs. Temperature
Output Control Current
I
OUTC
vs. Temperature
Output Voltage Range
V
R0
FS
V
OS
dV
OS
/dT
I
OUTOS
dI
OUTOS
/dT
I
OUTOS
dI
OUTOS
/dT
I
OUTC
dI
OUTC
/dT
V
OUT
V
OUT
Output Current Range FS
Output Resistance
Load Capacitance
Protection Functions
Voltage Limitation at
R
0
Temperature Limitation
Protection against reverse polarity
Current in case of reverse polarity
System Parameters
Nonlinearity
ideal input
0.05
V
LIMR0
V
LIMR0
T
LIMIT
Ground
vs.
V
S
vs.
I
OUT
Ground
= 35V,
V
S
=
I
OUT
= 0
3.8
V
R0
=
V
IN
G
IA
,
SET
=
GND
V
IN
= 0,
V
R0
=
V
SET
/2
580
580
110
640
635
130
I
OUTFS
R
OUT
C
L
G
VI
adjustable by
R
0
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
µV/°C
µA
nA/°C
µA
nA/°C
µA
nA/°C
V
CC
– 6
10
V
V
mA
MΩ
500
nF
β
F
≥
100
β
F
≥
100
3–wire operation
3–wire operation
2–wire operation
2–wire operation
2–wire operation,
V
R0
/100mV
2–wire operation
V
OUT
=
R
L
I
OUT
,
V
CC
< 16V
V
OUT
=
R
L
I
OUT
,
V
CC
≥
16V
I
OUT
=
V
R0
/R
0
, 3–wire operation
700
690
150
35
mV
mV
°C
V
mA
0.15
%FS
* In 2–wire operation a maximum current of
I
OUTmin
–
I
CC
is valid
Currents flowing into the IC are negative
BOUNDARY CONDITIONS
Parameter
Sense Resistor
Symbol
R
0
R
0
Stabilisation Resistor
R
5
R
5
Load Resistance
Sum Gain Resistors
Sum Offset Resistors
V
REF
Capacitance
Output Capacitance
D
1
Breakdown Voltage
T
1
Forward Current Gain
R
L
R
1
+
R
2
R
3
+
R
4
C
1
C
2
V
BR
only for 2–wire operation
Conditions
I
OUTFS
= 20mA
c
= 20mA/I
OUTFS
I
OUTFS
= 20mA
c
= 20mA/I
OUTFS
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
Ω
Ω
Ω
Ω
Ω
kΩ
kΩ
µF
nF
V
β
F
analog microelectronics
April 99
3/8
CURRENT CONVERTER IC
FUNCTIONAL DIAGRAMS
Reference Voltage
R
A
AM402
3−Wire System
V
S
V
V
IN
R
IN
IA
I
OUT
R
B
I
R
L
Ground
Figure 2
Reference Voltage
R
A
2−Wire System
V
S
V
V
IN
R
IN
IA
I
OUT
R
B
I
R
L
Ground
Figure 3
FUNCTIONAL DESCRIPTION
AM402 is a monolithically integrated current converter which has been specially developed for the proc-
essing 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
T
1
and a diode
D
1
are needed (See
Figure 7 and Figure 8) in addition to the resistors
R
0
–
R
5
and the capacitor
C
1
(C
2
). 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 transis-
tor and diode. Typical values for the external components are given in the following
Description of Appli-
cations.
AM402 can principally be used in the implementation of two- and three-wire systems for industrial applica-
tions. A schematic diagram illustrates a three-wire system in Figure 2. Here, the differential input voltage
(V
IN
) 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:
V
CC
=
V
S
. In two-wire configurations,
however (Figure 3), the ground of the IC (GND) is connected between resistors
R
5
and
R
L.
In this instance,
the supply voltage of the IC (V
CC
) is dependent on the supply voltage of the system (V
S
) and the value of the
load resistor (R
L
). It can be calculated using the equation:
analog microelectronics
April 99
4/8
CURRENT CONVERTER IC
V
CC
=
V
S
−
I
OUT
⋅
R
L
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
G
IA
is set via the two exter-
nal resistors
R
1
and
R
2
. When selecting the resistors, the sum of
R
1
+
R
2
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
R
3
and
R
4
(see the
Description of Applications,
begin-
ning on page 7). Output current
I
OUT
is provided by external transistor
T
1
which is driven by the output
(IOUT) of the IC. One particular feature of AM402 is that the output current is switched–off if overvolt-
age 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
C
1
(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 (V
IN
= 0).
In doing so, it should be ensured that the input pins of the instrumentation amplifier have the voltage poten-
tials given in the
Electrical Specifications
(input voltage range). The short circuit at the input produces an
output current
I
OUT
=
I
SET
with
I
SET
(
V
IN
=
0
)
=
V
REF
R
4
⋅
2
R
0
R
3
+
R
4
The adjustment of the output current range depends on the choice of external resistors
R
1
and
R
2
. The maxi-
mum output current is defined by the general transfer function of the IC. The following equation is given for
the output current
I
OUT
:
G
I
OUT
=
V
IN IA
+
I
SET
R
0
The gain factor of the instrumentation amplifier
G
IA
=
1
+
R
1
R
2
is determined by the input voltage
V
IN
and
the maximum output current
I
OUTmax
.
The minimum supply voltage is dependent on the value of the reference voltage. The following applies:
V
CC
≥
V
REF
+
1V
.
R
L
[Ω]
V
CCmin
=
6V
The choice of supply voltage
V
S
also de-
pends on the load resistor
R
L
used by the
application. The following inequation de-
termines the minimum supply voltage:
V
S
≥
I
OUTmax
R
L
+
V
CCmin
.
R
L
≤
V
S
−
V
CCmin
I
OUTmax
R
Lmax
=
500Ω
I
OUTmax
= 20mA
500
300
Operating Area
0
0
6
12
16
24
35
V
S
[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
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