LM19

SNIS122E – MAY 2001 – REVISED MARCH 2013

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Table 1. First Order Equations Optimized For Different Temperature Ranges

Temperature Range

Linear Equation

Maximum Deviation of Linear Equation from

VO=

Parabolic Equation (°C)

Tmin (°C)

Tmax (°C)

−55

+130

−11.79 mV/°C × T + 1.8528 V

±1.41

−40

+110

−11.77 mV/°C × T + 1.8577 V

±0.93

−30

+100

−11.77 mV/°C × T + 1.8605 V

±0.70

-40

+85

−11.67 mV/°C × T + 1.8583 V

±0.65

−10

+65

−11.71 mV/°C × T + 1.8641 V

±0.23

+35

+45

−11.81 mV/°C × T + 1.8701 V

±0.004

+20

+30

−11.69 mV/°C × T + 1.8663 V

±0.004

Mounting

The LM19 can be applied easily in the same way as other integrated-circuit temperature sensors. It can be glued

or cemented to a surface. The temperature that the LM19 is sensing will be within about +0.02°C of the surface

temperature to which the LM19's leads are attached.

This presumes that the ambient air temperature is almost the same as the surface temperature; if the air

temperature were much higher or lower than the surface temperature, the actual temperature measured would

be at an intermediate temperature between the surface temperature and the air temperature.

To ensure good thermal conductivity the backside of the LM19 die is directly attached to the GND pin. The

tempertures of the lands and traces to the other leads of the LM19 will also affect the temperature that is being

sensed.

Alternatively, the LM19 can be mounted inside a sealed-end metal tube, and can then be dipped into a bath or

screwed into a threaded hole in a tank. As with any IC, the LM19 and accompanying wiring and circuits must be

kept insulated and dry, to avoid leakage and corrosion. This is especially true if the circuit may operate at cold

temperatures where condensation can occur. Printed-circuit coatings and varnishes such as Humiseal and epoxy

paints or dips are often used to ensure that moisture cannot corrode the LM19 or its connections.

The thermal resistance junction to ambient (

θJA) is the parameter used to calculate the rise of a device junction

temperature due to its power dissipation. For the LM19 the equation used to calculate the rise in the die

temperature is as follows:

TJ = TA + θJA [(V

+ I

Q) + (V

+ − V

O) IL]

where

•

IQ is the quiescent current and ILis the load current on the output.

(6)

Since the LM19's junction temperature is the actual temperature being measured care should be taken to

minimize the load current that the LM19 is required to drive.

Table 2 summarizes the rise in die temperature of the LM19 without any loading, and the thermal resistance for

different conditions.

Table 2. Temperature Rise of LM19 Due to Self-Heating and Thermal Resistance (

θJA)

TO-92

TO-92

no heat sink

small heat fin

θJA

TJ − TA

θJA

TJ − TA

(°C/W)

(°C)

(°C/W)

(°C)

Still air

150

TBD

TBD

TBD

Moving air

TBD

TBD

TBD

TBD

6

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