Document
LM135-LM235-LM335
Precision temperature sensors
Features
■ Directly calibrated in °K ■ 1°C initial accuracy ■ Operates from 450µA to 5mA ■ Less than 1Ω dynamic impedance
Description
The LM135, LM235, LM335 are precision temperature sensors which can be easily calibrated. They operate as a 2-terminal Zener and the breakdown voltage is directly proportional to the absolute temperature at 10mV/°K.
The circuit has a dynamic impedance of less than 1Ω and operates within a range of current from 450µA to 5mA without alteration of its characteristics.
Calibrated at +25°C, the LM135, LM235, and LM335 have a typical error of less than 1°C over a 100°C temperature range. Unlike other sensors, the LM135, LM235, LM335 have a linear output.
TO-92 (Plastic package)
SO-8 (Plastic micropackage)
Pin connections
TO-92 (Bottom view)
ADJ v+ v-
SO-8 (Top view)
V+
NC
NC ADJ
8
7
6
5
1
2
3
NC NC
NC
4 V
-
February 2008
Rev 3
1/16
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16
Schematic diagram
1
Schematic diagram
Figure 1. Schematic diagram
LM135-LM235-LM335
2
Absolute maximum ratings
Table 1. Absolute maximum ratings (AMR)
Symbol
Parameter
LM135
LM235
LM335LM335A
Unit
Current
IR IF
Reverse Forward
Toper
Operating free-air temperature range(1)
Continuous Intermittent
Tstg Storage temperature range
1. Tj ≤ 150°C
15
mA
10
°C -55 to +150 -40 to +125 -40 to +100 +150 to +200 +125 to +150 +100 to +125
-65 to +150
°C
2/16
LM135-LM235-LM335
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Temperature accuracy
Temperature accuracy
Table 2. Temperature accuracy
Parameter
Operating output voltage Tcase = +25°C, IR = 1mA Uncalibrated temperature error (IR = 1mA)
Tcase = +25°C Tmin ≤ Tcase ≤ Tmax Temperature error with 25°C calibration Tmin ≤ Tcase ≤ Tmax., IR = 1mA LM135 - LM235 LM335 LM335A
Calibrated error at extended temperature Tcase = Tmax (intermittent) Non-linearity (IR = 1mA)
LM135 - LM235 LM335 LM335A
LM135 - LM235 LM335A
LM335 Unit
Min. Typ. Max. Min. Typ. Max.
2.95 2.98 3.01 2.92 2.98 3.04 V
1
3
2
5
4
6
°C
5
9
0.5 1.5
0.5
1
2
0.3
1
0.3 1.5
°C
1
2
2
°C
°C 0.3 1.5
4
Electrical characteristics
Table 3. Electrical characteristics Parameter
LM135 - LM235
LM335-LM335A
Unit
Min. Typ. Max. Min. Typ. Max.
Operating output voltage change with current 450µA ≤ IR ≤ 5mA at constant temperature
Dynamic impedance (IR = 1mA) Output voltage temperature drift
Time constant Still air Air 0.5m/s Stirred oil
Time stability (Tcase = +125°C)
2.5 10 0.5 +10
80 10 1 0.2
3
14 mV
0.6
Ω
+10
mV/°C
80
s
10
1
0.2
°C/kh
Note:
Accuracy measurements are made in a well-stirred oil bath. For other conditions, selfheating must be considered
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Electrical characteristics Figure 2. Reverse voltage change
LM135-LM235-LM335 Figure 3. Calibrated error
Calibrated error (°C)
Reverse voltage change (mV)
Reverse current (mA) Figure 4. Reverse characteristics
Temperature (°C) Figure 5. Response time
Voltage swing (V)
Reverse current (mA)
Reverse voltage (V) Figure 6. Dynamic impedance
Time (µs) Figure 7. Noise voltage
Noise (nV/√Hz)
Dynamic impedance (Ohm)
Frequency (Hz) 4/16
Frequency (Hz)
LM135-LM235-LM335
Electrical characteristics
Figure 8. Thermal resistance junction to air Figure 9. Thermal time constant
Time constant (s)
Thermal resistance (°C/W)
Air velocity (m/s) Figure 10. Thermal response in still air
Air velocity (m/s) Figure 11. Thermal response in stirred oil bath
Percent of final value (%)
Percent of final value (%)
Time (min) Figure 12. Forward characteristics
Time (s)
Forward voltage (V)
Forward current (mA) 5/16
Application information
5
Application information
LM135-LM235-LM335
There is an easy method of calibrating the device for higher accuracies (see Typical applications).
The single point calibration works because the output of the LM135, LM235, LM335 is proportional to the absolute temperature with the extrapolated output of sensor going to 0V at 0°K (-273.15°C). Errors in output voltage versus temperature are only slope. Thus a calibration of the slope at one temperature corrects errors at all temperatures.
The circuit output (calibrated or not) is given by the equation:
VOT + VOTO x
--T---To
where T is the unknown temperature and To is the reference temperature (in °K).
Nominally, the output is calibrated at 10mV/°K.
Precautions should be taken to ensure good sensing accuracy. As in the case of all temperatures sensors, self-heating can decrease accuracy. The LM135, LM235, and LM335 should operate with a low current but sufficient to drive the sensor and its calibration circuit to their maximum operating temperature.
If the sensor is used in surroundings where the thermal resistance is constant, the errors due to self-heating can be externally calibrated. This is possible if the circuit is biased with a temperature stable current. Heating will then be proportional to Zener voltage and therefore temperature. In this way, the error du.