AD590
CMOS analog multiplexers can also be used to switch AD590
current. Due to the AD590’s current mode, the resistance of
such switches is unimportant as long as 4 V is maintained
across the transducer. Figure 24 shows a circuit that combines
the principle demonstrated in Figure 23 with an 8-channel
CMOS multiplexer. The resulting circuit can select 1 to 80
sensors over only 18 wires with a 7-bit binary word.
The inhibit input on the multiplexer turns all sensors off for
minimum dissipation while idling.
Figure 25 demonstrates a method of multiplexing the AD590 in
the 2-trim mode (see Figure 12 and Figure 13). Additional AD590s
and their associated resistors can be added to multiplex up to
eight channels of 0.5°C absolute accuracy over the temperature
range of −55°C to +125°C. The high temperature restriction of
125°C is due to the output range of the op amps; output to
150°C can be achieved by using a 20 V supply for the op amp.
10V
0
1
2
16
3
14
2
4028
CMOS
+
–
+
–
+
–
+
–
+
–
+
–
AD590
00
BCD-TO-
DECIMAL
DECODER
+
–
+
–
+
–
02
01
12
11
10
11
12
13
10
22
21
20
ROW
SELECT
8
10V
16
2
1
0
15 14 13
9
LOGIC
LEVEL
INTERFACE
4051 CMOS ANALOG
MULTIPLEXER
10
COLUMN
SELECT
11
6
INHIBIT
BINARY TO 1-OF-8 DECODER
7
8
10kΩ 10mV/°C
Figure 24. Matrix Multiplexer
2kΩ
2kΩ
5kΩ
35.7kΩ
35.7kΩ
97.6kΩ
+15V
5kΩ
+
–
97.6kΩ
AD581
V
OUT
V+
S1
S2
AD707A
10mV/°C
DECODER/
DRIVER
–15V
27kΩ
S8
AD7501
+15V
–15V
TTL/DTL TO CMOS
INTERFACE
+
–
+
EN
BINARY
CHANNEL
SELECT
AD590L
AD590L
–
–5V TO –15V
Figure 25. 8-Channel Multiplexer
Rev. D | Page 12 of 16
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