TMP01GBC AD [Analog Devices], TMP01GBC Datasheet - Page 15

• Manufacturer Part Number: TMP01GBC
• Description: Low Power, Programmable Temperature Controller
• Manufacturer: AD [Analog Devices]

REV. C
Translating 5 mV/K to 10 mV/ C
A useful circuit is shown in Figure 23 that 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 will exactly cancel the VPTAT voltage at 0.0 C.
TMP01
VPTAT
VREF
Figure 23. Translating 5 mV/K to 10 mV/ C
1
5
4.12k
100k
100k
487
TMP01
VPTAT
VREF
3
105k
2
OP177
1
5
10pF
+15V
–15V
7
4
6.49k
4.22k
100k
6
100k
121
Figure 24. Translating 5 mV/K to 10 mV/ F
V
(V
OUT
OUT
3
90.9k
2
(10mV/ C)
= 0.0V @ T = 0.0 C)
–15V
10pF
+15V
7
4
1.0k
OP297
1/2
6
–15–
100k
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 bet-
ter accuracy, a adjustment potentiometer can be added in series
with either 100 k resistor.
Translating VPTAT to the Fahrenheit Scale
A very similar circuit to the one shown in Figure 23 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 con-
version to the Fahrenheit scale. Using the circuit in Figure 24, a
temperature of 0.0 F gives an output of 0.00 V. At room tem-
perature (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 23.
6
5
100k
OP297
1/2
7
V
(10mV/ F)
OUT
= 0.0V @ T = 0.0 F
TMP01