Datasheet

TMP01
Rev. E | Page 16 of 20
TRANSLATING 5 mV/K TO 10 mV/°C
A useful circuit shown in Figure 31 translates the VPTAT
output voltage, which is calibrated in Kelvins, into an output
that can be read directly in degrees Celsius on a voltmeter
display.
To accomplish this, an external amplifier is configured as a
differential amplifier. The resistors are scaled so the VREF
voltage exactly cancels the VPTAT voltage at 0.0°C.
5
1
+15V
–15V
10pF
V
OUT
= (10mV/°C)
(V
OUT
= 0.0V @ T = 0.0°C)
VPTAT
VREF
TMP01
OP177
7
4
3
6
2
100kΩ
100kΩ
105kΩ 4.22kΩ
4.12kΩ 487Ω
00333-031
Figure 31. Translating 5 mV/K to 10 mV/°C
However, the gain from VPTAT to the output is two, so that
5 mV/K becomes 10 mV/°C. Thus, for a temperature of 80°C,
the output voltage is 800 mV. Circuit errors will be due prima-
rily to the inaccuracies of the resistor values. Using 1% resistors,
the observed error was less than 10 mV, or 1°C. The 10 pF
feedback capacitor helps to ensure against oscillations. For
better accuracy, an adjustment potentiometer can be added in
series with either 100 k resistor.
TRANSLATING VPTAT TO THE FAHRENHEIT SCALE
A similar circuit to the one shown in Figure 31 can be used
to translate VPTAT into an output that can be read directly in
degrees Fahrenheit, with a scaling of 10 mV/°F. Only unity gain
or less is available from the first stage differentiating circuit, so
the second amplifier provides a gain of two to complete the
conversion to the Fahrenheit scale. Using the circuit in Figure 32,
a temperature of 0.0°F gives an output of 0.00 V. At room temp-
erature (70°F), the output voltage is 700 mV. A −40°C to +85°C
operating range translates into −40°F to +185°F. The errors are
essentially the same as for the circuit in Figure 31.
5
1
+15V
–15V
10p
F
V
OUT
= 0.0V @ T = 0.0°F
(10mV/°F)
VPTAT
VREF
TMP01
1/2
OP297
7
4
3
6
2
100kΩ
100kΩ
90.9kΩ 1.0kΩ
1/2
OP297
5
7
6
100kΩ
6.49kΩ 121Ω
100kΩ
00333-032
Figure 32. Translating 5 mV/K to 10 mV/°F