Datasheet

23
LTC1292/LTC1297
12927fb
U
S
A
O
PP
L
IC
AT
I
WU
U
I FOR ATIO
Opto-Isolated Temperature Monitor
Amplification of sensor outputs is often required to
generate a signal large enough to be properly digitized.
For example, a J-type thermocouple provides only
52µV/°C. The 5µV offset of the LTC1050 chopper op
amp generates less than 0.1°C error (Figure 31). Cold
junction compensation is provided by the LT1025A.
(For more detail see LTC Design Note 5).
In the opto-isolated interface two signals are generated
from one. This allows a two-wire interface to the
LTC1292. A long high signal (>1ms) on the CLK IN input
allows the 0.1µF capacitor to discharge taking CS high.
This resets the A/D for the next conversion. When CLK
IN starts toggling, CS goes low and stays there until the
next extended CLK IN high time. See Figure 30.
5V/DIV
A
CLK IN
CS
DATA OUT
20µs/DIV
+
1 F
TYPE J
J
R
GND
LT1025A
V
IN
H
2
2
3
–
+
LTC1050
7
4
6
+
µ
0.33 Fµ
178k
0.1%
3.4k
0.1%
2k
0.1%
47Ω
+
1 Fµ
GND
LTC1292
V
CC
–IN
+IN
CS
CLK
D
OUT
V
REF
+
4.7 Fµ
3Ω
+
0.1 Fµ
10k
1N4148
8
7
6
5
1
2
3
4
+
22 Fµ
LT1019-2.5
500k
1
2
1k
CLK IN
3
4
500k
3
4
5k
DATA
OUT
1
2
6
1k
4N28s
1N4148
0°C – 500°C TEMPERATURE RANGE
ISOLATED
5V
4
5
+
–
A
6
100k
74C14
5V
5V
5k
LTC1292/7 F31
1N4148
Figure 31. Opto-Isolated Temperature Monitor
Figure 30. Opto-Isolated Temperature
Monitor Digital Waveforms
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.