AC1059 Datasheet, PDF (7/8 Pages) Analog Devices – Precision, Wide Bandwidth 3-Port Isolation Amplifier

AD210
lent current V_OUT/2 kΩ. This resistor directly affects the output
gain temperature coefficient, and must be of suitable stability for
the application. The external low power op amp, powered by
+V_OSS and –V_OSS, maintains its summing junction at output
common. All the current flowing through the 2 kΩ resistor flows
through the output Darlington pass devices. A Darlington con-
figuration is used to minimize loss of output current to the base.
16
V_SIG
17
0-10V ₁₉
18
14 +V_ISS
2kΩ
1
AD210
2
FDH333
+V_OSS
LF441
–V_OSS
+V_OSS ³
2N3906
(2)
I_OUT
15 –V_ISS
30 29
–V_OSS ⁴
I_OUT
RETURN
+15V
Figure 18. Self-Powered Isolated Current Source
The low leakage diode is used to protect the base-emitter junc-
tion against reverse bias voltages. Using –V_OSS as a current
return allows more than 10 V of compliance. Offset and gain
control may be done at the input of the AD210 or by varying
the 2 kΩ resistor and summing a small correction current
directly into the summing node. A nominal range of 1 mA–
5 mA is recommended since the current output cannot reach
zero due to reverse bias and leakage currents. If the AD210 is
powered from the input potential, this circuit provides a fully
isolated, wide bandwidth current output. This configuration is
limited to 5 mA output current.
Isolated V-to-I Converter
Illustrated in Figure 19, the AD210 is used to convert a 0 V to
+10 V input signal to an isolated 4–20 mA output current. The
AD210 isolates the 0 V to +10 V input signal and provides a
proportional voltage at the isolator’s output. The output circuit
converts the input voltage to a 4–20 mA output current, which
in turn is applied to the loop load R_LOAD.
ADJUST
TO 4mA
WITH 0V IN
3.0k
500Ω
143Ω
+28V
CURRENT
LOOP
2N2907
16
17
V_{SIG 19}
18
14 +V_ISS
1
AD210
2
+V_S
AD308
–V_S
+V_OSS ³
SPAN
ADJ
2N2219
576Ω
100Ω
15 –V_ISS
30 29
+15V
–V_OSS ⁴
1N4149
CURRENT
LOOP
R_LOAD
Figure 19. Isolated Voltage-to-Current Loop Converter
Isolated Thermocouple Amplifier
The AD210 application shown in Figure 20 provides amplifica-
tion, isolation and cold-junction compensation for a standard J
type thermocouple. The AD590 temperature sensor accurately
monitors the input terminal (cold-junction). Ambient tempera-
ture changes from 0°C to +40°C sensed by the AD590, are can-
celled out at the cold junction. Total circuit gain equals 183;
100 and 1.83, from A1 and the AD210 respectively. Calibration
is performed by replacing the thermocouple junction with plain
thermocouple wire and a millivolt source set at 0.0000 V (0°C)
and adjusting R_O for E_OUT equal to 0.000 V. Set the millivolt
source to +0.02185 V (400°C) and adjust R_G for V_OUT equal to
+4.000 V. This application circuit will produce a nonlinearized
output of about +10 mV/°C for a 0°C to +400°C range.
–V_ISS R_G
AD590
5k
1000pF
THERMAL
CONTACT
"J"
13.7k 10k
16
AD OP-07
17
A1
19
52.3Ω
COLD
JUNCTION
R_G
10k
-20k-
–V_ISS +V_ISS
220pF
1k ^100k
18
14 +V_ISS
15 –VISS
V_OUT
1
AD210
2
30 29
+15V
+V_OSS 3
–V_OSS 4
Figure 20. Isolated Thermocouple Amplifier
Precision Floating Programmable Reference
The AD210, when combined with a digital-to-analog converter,
can be used to create a fully floating voltage output. Figure 21
shows one possible implementation.
The digital inputs of the AD7541 are TTL or CMOS compat-
ible. Both the AD7541 and AD581 voltage reference are pow-
ered by the isolated power supply + V_ISS. I_COM should be tied to
input digital common to provide a digital ground reference for
the inputs.
The AD7541 is a current output DAC and, as such, requires an
external output amplifier. The uncommitted input amplifier
internal to the AD210 may be used for this purpose. For best
results, its input offset voltage must be trimmed as shown.
The output voltage of the AD210 will go from 0 V to –10 V for
digital inputs of 0 and full scale, respectively. However, since
the output port is truly isolated, V_OUT and O_COM may be freely
interchanged to get 0 V to +10 V.
This circuit provides a precision 0 V–10 V programmable refer-
ence with a ± 3500 V common-mode range.
GAIN
+V_ISS
2kΩ
AD581
+V_ISS
17 16
4
12-BIT
DIGITAL
INPUT
15
18
1
2
3
1kΩ
16
17
19
200Ω
18
V_OUT
1
0 - –10V
AD210
2
HP5082-2811
OR EQUIVALENT
50kΩ
14
100kΩ
15
OFFSET
+V_ISS
–V_ISS
+V_OSS ³
–V_OSS 4
30 29
+15V
Figure 21. Precision Floating Programmable Reference
REV. A
–7–