Temperature measurement IC provides protection

Directly digitising combinations of thermocouples, RTDs, thermistors and external diodes with 0.1°C conformity and 0.001°C resolution, the LTC2986 digital temperature measurement IC has been released by Linear Technology.

It adds three new operating modes to existing ICs from the company, and halves the number of analogue inputs from 20 to 10 channels. The operating modes provide better support for external over-voltage protection resistors that are shared between multiple sensor types, powered temperature sensors with analogue outputs, and other non-temperature related sensors, such as pressure or other voltage output sensors.

The analogue front end combines low noise and low offset buffered ADCs with all the necessary excitation and control circuits for each sensor. Measurements are controlled by a digital engine, combining all the algorithms and linearisation required for each. The device measures absolute microV level signals from thermocouples and ratiometric resistance measurements from RTDs and thermistors. It also performs the linearisation and outputs the results in Celsius or Fahrenheit. Up to 10 analogue inputs are available, allowing support for up to nine thermocouples, four RTDs, four thermistors and/or 10 diodes. The SPI works with virtually any digital system and a comprehensive software support system with drop-down menus allows easy customisation of the IC.

The IC interfaces with a variety of temperature sensors, including type B, E, J, K, N, S, R, T thermocouples, two-, three- or four-wire RTDs, 2.25 to 30kOhm thermistors and temperature sensing diodes. The IC works with ground-referenced sensors without the need of amplifiers, negative supplies or level shift circuitry.  Signals are simultaneously digitised with three, high accuracy, 24bit delta sigma ADCs using an internal 15ppm/degree C reference. Automatic thermocouple cold junction compensation is accomplished using any type of external sensor. Included on the chip are linearisation algorithms for all common sensor types. Custom sensors can be linearised with custom co-efficients, programmed and stored in the chip.  Onboard EEPROM (LTC2986-1) is used to store user configuration data and custom sensor co-efficients, eliminating any IC or sensor programming by a host processor.  Dual programmable excitation current sources feature current reversal and current ranging to improve accuracy and reduce noise. Current reversal eliminates thermocouple effects in the resistive sensor. Sensor-specific fault detection alerts the user of short-circuits, open-circuits, over-temperature, under-temperature and ADC over-ranging.

Commercial, industrial and automotive versions are available, supporting operating temperature ranges from 0 to 70,-40 to 85 and – 40 to 125 degree C, respectively. The RoHS-compliant, 7.0 x 7.0mm LQFP-48 package is available now.



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