LM20

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SNIS106P – DECEMBER 1999 – REVISED FEBRUARY 2013

where T is the middle of the temperature range of interest and m is in V/°C. For example for the temperature

T = 35°C

(5)

and

m =

−11.77 mV/°C

(6)

The offset of the linear transfer function can be calculated using the following equation:

(7)

where:

•

•

Using this procedure the best fit linear transfer function for many popular temperature ranges was calculated in

Table 2. As shown in Table 2 the error that is introduced by the linear transfer function increases with wider

temperature ranges.

Table 2. First Order Equations Optimized for Different Temperature Ranges

Temperature Range

Linear Equation

Maximum Deviation of Linear Equation from

Parabolic Equation (°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 LM20 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 LM20 is sensing will be within about +0.02°C of the surface

temperature to which the LM20's leads are attached to.

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 LM20 die is directly attached to the pin 2 GND pin. The

tempertures of the lands and traces to the other leads of the LM20 will also affect the temperature that is being

sensed.

Alternatively, the LM20 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 LM20 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 LM20 or its connections.

The thermal resistance junction to ambient (

temperature due to its power dissipation. For the LM20 the equation used to calculate the rise in the die

temperature is as follows:

is the actual temperature being measured care should be taken to minimize the load current that the LM20 is

required to drive.

The tables shown in Table 3 summarize the rise in die temperature of the LM20 without any loading, and the

thermal resistance for different conditions.

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