TMP01FS datasheet(16/20 Pages) AD

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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.

+15V

–15V

10pF

VOUT = (10mV/°C)

(VOUT = 0.0V @ T = 0.0°C)

VPTAT

VREF

TMP01

OP177

100k

Ω

100k

Ω

105k

Ω

4.22k

Ω

4.12k

Ω

487

Ω

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 kΩ 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.

+15V

–15V

10pF

VOUT = 0.0V @ T = 0.0°F

(10mV/°F)

VPTAT

VREF

TMP01

1/2

OP297

100k

Ω

100k

Ω

90.9k

Ω

1.0k

Ω

1/2

OP297

100k

Ω

6.49k

Ω

121

Ω

100k

Ω

Figure 32. Translating 5 mV/K to 10 mV/°F

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