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Maxim > Design Support > Technical Documents > Application Notes > Amplifier and Comparator Circuits > APP 4542
Maxim > Design Support > Technical Documents > Application Notes > Temperature Sensors and Thermal Management > APP 4542
Keywords: temperature measurements, IC temperature sensors, temperature-to-period converters,
comparators, twisted-pair cable
APPLICATION NOTE 4542
Long Twisted Pair Reads Digital Temperature Sensor
Dec 10, 2010
Abstract:
This circuit
is a simple and economical interface for remote IC thermal sensors. The temperature
sensor (MAX6576), an absolute temperature-to-period converter that integrates the sensor with the necessary
signal electronics, connects to the receiver (a MAX9140 comparator) using a twisted-pair cable that carries
power to and signals from the sensor.
A similar version of this article appeared in the November 5, 2007 issue of Electronic Design magazine.
The best choice for midrange, low-to-medium-accuracy temperature measurements (considering size, cost,
performance, and ease of use) is an IC temperature sensor—assuming the circuits to be interfaced with the
sensor reside on the same board or in the same box. Most IC temperature sensors are designed for
applications in which the circuits to which they connect are nearby, so the inclusion of sensing, digitizing, and
signal-processing functions in a single IC greatly simplifies the design of such sensors and the data-
acquisition interface.
Some applications, however, require the acquisition of temperature data from locations quite remote from the
power supply and data-processing electronics. You must exercise extra care with such systems, because any
deterioration in the signal from the remote sensor can degrade the measurement quality.
Choosing to digitize and process the signal at the point of measurement (near the sensor) greatly reduces the
problem of signal integrity, but that approach also complicates the interconnection and raises the problem of
supplying power to the circuit. Either design option (signal processing remote or at the sensor) requires cabling
that is complex or expensive or both.
The circuit of Figure 1 provides a simple and economical interface for remote IC thermal sensors. The
temperature sensor (MAX6576) is an absolute temperature-to-period converter that integrates the sensor with
the necessary signal electronics. It connects to the receiver (a simple comparator) using a twisted-pair cable
that simultaneously carries power to the sensor and signals from the sensor.
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