AN2648

STLM20 temperature-to-output transfer function

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The second issue arises with the output voltage range. The micro's ADC performs ratio-

Referring to Figure 3, while the ADC can accept inputs over the full range 0 to 5 V, the

temperature sensor output will vary over a much smaller range, between 0.87 and 2.33 volts

across the temperature range –40° to +85°C.

Figure 3.

STLM20 output voltage range

This amounts to using only 1.46 V of the available 5 V range. Furthermore, in the intended

demonstration board application, the necessary temperature range was approximately room

temperature –15°/+25°, or 10° to 50°C.

For this target temperature range, the voltage range is 1.28 to 1.75 V, an interval of less than

0.5 V, less than one tenth the available 5 V range. This is depicted in Figure 4.

55

2

)

/V

V

(

(dec)

output

ADC

CC

IN

×

=

51

V

55

2

/5)

V

(

(dec)

output

ADC

IN

IN

×

=

×

=

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

-60

-40

-20

0

20

40

60

80

100

Temperature, T

Available

voltage

range

STLM20

output voltage

range

STLM20 full range,

linear, ind temp

ai13987