Book Analog Interfacing to Embedded Microprocessors
sensing element. The transistor can be a discrete part, or it can be embedded
in the die of an IC to measure the IC temperature. The MAX1617 has a serial
SMBus output.
The LM335 (Figure 3.5) from National Semiconductor produces an output
voltage proportional to temperature. The LM135 produces 10 mv per degree
Kelvin. At 0°C, the output is 2.73v, and at 100°C the output is 3.73v. The
LM335 operates with input current from 400 ma to 5 ma.
The National LM34 and LM35 sensors operate from supply voltages
between 4v and 20v, and produce a voltage output that directly corresponds
to voltage. The LM35 produces a voltage of 500 mv at 50°C, with an additional
10 mv for every additional °C increase. The LM34 is calibrated for Fahrenheit
temperatures, and the LM35 for Centigrade. The outputs of the LM34/LM35
can be connected directly to an ADC or to a comparator.
Figure 3.5
LM335.
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