TMP112
SBOS473B–MARCH 2009–REVISED JUNE 2009 ......................................................................................................................................................... www.ti.com
USING THE SLOPE SPECIFICATIONS WITH A
1-POINT CALIBRATION
Using the previous example temperature range of
0°C to +50°C, the worst-case temperature error is
now reduced to the worst-case slopes because the
offset at +25°C (that is, the maximum and minimum
temperature errors of +0.3°C and –0.5°C) is removed.
Therefore, a user can expect the worst-case accuracy
to improve to +0.175°C.
The initial accuracy assurance at +25°C with the
slope regions provides an accuracy that is high
enough for most applications; however, if higher
accuracy is desired, this increase can be achieved
with a 1-point calibration at +25°C. This calibration
removes the offset at room temperature, thereby
Power-Supply Level Contribution to Accuracy
reducing the source of error in
a
TMP112
temperature reading down to the curvature. Figure 20
shows the error of a calibrated TMP112.
The superior accuracy that can be achieved with the
TMP112 is complemented by its immunity to dc
variations from a 3.3V supply voltage. This immunity
is important because it spares the user from having to
use another LDO to produce 3.3V to achieve
accuracy. Nevertheless, the noise quantization that
results from changing supply can add some slight
change in temperature measurement accuracy. As an
example, if the user chooses to operate at 1.8V, the
worst-case expected change in accuracy can be
calculated by Equation 14:
0.8
Slope3MAX
0.6
0.4
Slope1MAX
Slope2MAX
0.2
0
-0.2
-0.4
-0.6
+0.250°C
Calibration at +25°C Removes Offset
AccuracyPSR = ±(VS - 3.3V) ´
V
(14)
+0.250°C
AccuracyPSR = ±(1.8V - 3.3V) ´
= +0.375°C
-40-30 -20 -10
0
10 20 30 40 50 60 70 80 90 100 110120 130
V
Temperature (°C)
(15)
This example is a worst-case accuracy contribution
as a result of variation in power supply that should be
added to the accuracy + slope maximum.
Figure 20. Calibrated Accuracy and Slope Curves
versus Temperature
18
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