EDN -- 03.14.96 Temperature sensors fill different needs

Out in Front: March 14, 1996

Temperature sensors fill different needs

Two temperature-sensor ICs from National Semiconductor offer different attributes. The LM75 includes a software-programmable threshold to signal overtemperature. The device has a bandgap sensor; a noise-resistant, 9-bit sigma-delta A/D converter providing resolution of 0.5°C; and a comparator with hysteresis. The device interfaces to the processor via the two-wire I²C bus. When the temperature rises above the setpoint, the IC produces an open-drain output signal, which you can use to interrupt the processor or directly control cooling circuitry.

As an added defense against noise-induced false triggering, you can instruct the LM75 to require one, two, four, or six successive overtemperature comparisons (based on the 100-msec conversion time of the A/D converter) before the LM75 generates the output alarm. You can multidrop as many as eight LM75s on the I²C bus and read the sensor temperature at any time. Accuracy is ±2% from -25 to +100°C. The 3.3 to 5V device is available in an eight-lead SOIC and consumes 250 µA in operation and 10 µA in sleep mode. The LM75 costs $1.40 (1000).

For applications requiring smaller size and lower-voltage operation, the LM60 puts an analog-output sensor in an SOT-23 package. This device operates as low as 2.7V and provides a linear output of 6.25 mV/°C from -40 to +125°C; accuracy from -25 to +100° is ±3°. The LM60 requires no external signal conditioning, calibration, or correction and consumes 90 µA. It costs $1.10 (1000).
—by Bill Schweber

National Semiconductor Corp, Santa Clara, CA. (800) 272-9959.