Datasheet

LM73

www.ti.com

SNIS141D –OCTOBER 2005–REVISED MAY 2009

APPLICATION HINTS

THERMAL PATH CONSIDERATIONS

To get the expected results when measuring temperature with an integrated circuit temperature sensor like the

LM73, it is important to understand that the sensor measures its own die temperature. For the LM73, the best

thermal path between the die and the outside world is through the LM73's pins. In the SOT package, all the pins

on the LM73 will have an equal effect on the die temperature. Because the pins represent a good thermal path to

the LM73 die, the LM73 will provide an accurate measurement of the temperature of the printed circuit board on

which it is mounted. There is a less efficient thermal path between the plastic package and the LM73 die. If the

ambient air temperature is significantly different from the printed circuit board temperature, it will have a small

effect on the measured temperature.

OUTPUT CONSIDERATIONS: TIGHT ACCURACY, RESOLUTION AND LOW NOISE

The LM73 is well suited for applications that require tight temperature measurement accuracy. In many

applications, the low temperature error can mean better system performance and, by eliminating a system

calibration step, lower production cost.

With digital resolution as fine as 0.03125 °C/LSB, the LM73 senses and reports very small changes in its

temperature, making it ideal for applications where temperature sensitivity is important. For example, the LM73

enables the system to quickly identify the direction of temperature change, allowing the processor to take

compensating action before the system reaches a critical temperature.

The LM73 has very low output noise, typically 0.015°C rms, which makes it ideal for applications where stable

thermal compensation is a priority. For example, in a temperature-compensated oscillator application, the very

small deviation in successive temperature readings translates to a stable frequency output from the oscillator.

POWER SUPPLY RAMP-UP CONSIDERATIONS

In systems where there is a large amount of capacitance on the VDD node, the LM73 power supply ramp-up

time can become excessively long. Slow power-supply ramp times may result in abnormal temperature readings.

A linear power-on-ramp of less than 0.7V/msec and an exponential ramp with an RC time constant of more than

1.25 msec is categorized as a slow power-supply ramp. To avoid errors, use the power up sequence described

below.

The software reset sequence is as follows:

1. Allow V

to reach the specified minimum operating voltage, as specified in the Operating Ratings section.

2. Write a “1” to the Full Power Down bit, Bit 7 of the Configuration Register, and hold it high for the specified

maximum conversion time for the initial default of 11-bits resolution. This ensures that a complete reset

operation has occurred. See the Temperature Conversion Time specifications within the TEMPERATURE-

TO-DIGITAL CONVERTER CHARACTERISTICS section for more details.

3. Write a “0” to the Full Power Down bit to restore the LM73 to normal mode.

Product Folder Links: LM73