Datasheet AD210 (Analog Devices) - 8

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