TMP01

REV. C

–15–

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.

5

1

+15V

–15V

10pF

V

OUT

(10mV/

°C)

(V

OUT

= 0.0V @ T = 0.0

°C)

487

Ω

7

6

4

3

2

OP177

100k

Ω

100k

Ω

4.12k

Ω

VPTAT

VREF

TMP01

4.22k

Ω

105k

Ω

Figure 23. 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 bet-

ter accuracy, a adjustment potentiometer can be added in series

with either 100 k

Ω 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.

V

OUT

= 0.0V @ T = 0.0

°F

(10mV/

5

1

+15V

–15V

10pF

121

Ω

7

6

4

3

2

1/2

OP297

100k

Ω

100k

Ω

6.49k

Ω

VPTAT

VREF

TMP01

1.0k

Ω

90.9k

Ω

100k

Ω

7

6

5

1/2

OP297

100k

Ω

Figure 24. Translating 5 mV/K to 10 mV/

°F