23

LTC1292/LTC1297

S

APPLICATI

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

52

µV/°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 0.1

µF 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

20

µs/DIV

+

1 F

TYPE J

J

R

GND

LT1025A

H

2

2

3

–

+

LTC1050

7

4

6

µ

0.33 F

µ

178k

0.1%

3.4k

0.1%

2k

0.1%

47

Ω

+

1 F

µ

GND

LTC1292

–IN

+IN

CS

CLK

+

4.7 F

µ

3

Ω

+

0.1 F

µ

10k

1N4148

8

7

6

5

1

2

3

4

+

22 F

µ

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.