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LM134-3

Constant Current Source and Temperature Sensor

Linear Technology 

LM134 Series

APPLICATIO S I FOR ATIO

The two trims shown in Figure 3 are still intended to be a

“one point” temperature calibration, where the zero and

the slope are trimmed at a single temperature. The LT1009

reference is adjusted to give 2.700V at node “a” at TSENSOR

= 25°C. The 1k trimmer then adjusts the output for 0.25V,

completing the calibration. If the calibration is to be done

at a temperature other than 25°C , trim the LT1009 for

2.7025—(1µA)[TSENSOR (°C)](100Ω) at node “a”, then

adjust the 1k trimmer for proper output.

VS ≥ 4V

V+

LM134-3

R

OUTPUT

10mV/°C

V–

9.53k

1%

1k

SLOPE

ADJ

LT1009

100Ω

“a”

10k

RSET

226Ω

–15V

10k

ZERO

ADJ

134 F03

Figure 3. Centigrade Temperature Sensor

If higher accuracy is required, a two point calibration

technique can be used. In Figure 4, separate zero and slope

trims are provided. Residual nonlinearity is now the limi-

tation on accuracy. Nonlinearity of the LM134 in a 100°C

span is typically less than 0.5°C. This particular method of

trimming has the advantage that the slope trim does not

interact with the zero trim. Trim procedure is to adjust for

zero output with TSENSOR = 0°C, then trim slope for proper

output at some convenient second temperature. No fur-

ther trimming is required.

V+

LM134-3

R

V+ ≥ 5V

226Ω*

V–

*LOW TC, STABLE RESISTOR

50k

SLOPE

TRIM

500k

332k

11k*

1%

1%

15k

LT1009

OUTPUT

10mV/°C

ZERO

TRIM

10k

–15V

134 F04

Figure 4. Centigrade Temperature Sensor with 2 Point Trim

TYPICAL APPLICATIO S

Basic 2-Terminal

Current Source

VIN

V+

ISET

R

LM334 V–

RSET

–VIN

134 TA02

Low Output Impedance

Thermometer (Kelvin Output)

VIN ≥ 4.8V

V+

R

LM334 V–

R3*

600Ω

R1

230Ω

1%

VOUT = 10mV/°K

ZOUT ≤ 100Ω

C1

0.1µF

R2

10k

1%

134 TA03

*OUTPUT IMPEDANCE OF THE LM134 AT THE “R” PIN IS

APPROXIMATELY

–RO

16

Ω,

WHERE

RO

IS

THE

EQUIVALENT

EXTERNAL RESISTANCE CONNECTED TO THE V– PIN. THIS

NEGATIVE RESISTANCE CAN BE REDUCED BY A FACTOR OF

5 OR MORE BY INSERTING AN EQUIVALENT RESISTOR IN

SERIES WITH THE OUTPUT.

Zero Temperature

Coefficient Current Source

VIN

I+

V+

R

LM334 V–RSET

D1

1N457

R1*

≈10 RSET

–VIN

134 TA04

*SELECT

OBTAIN

RATIO OF R1

ZERO DRIFT.

IT+O≈R2SIESTETT.O

7

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