Temperature Measurement IC Linearizes Sensors to 0.1° C Conformity

13 September 2016

Linear Technology Corporation has introduced the LTC2986 high- performance digital temperature measurement IC, which directly digitizes any combination of thermocouples, RTDs, thermistors and external diodes with 0.1° C conformity and 0.001° C resolution. The LTC2986 builds on the existing LTC2983 and LTC2984 ICs by adding three new operating modes and reducing the number of analog inputs from 20 channels to 10 channels. The operating modes provide better support for external overvoltage protection resistors that are shared between multiple sensor types, powered temperature sensors with analog outputs, and other non-temperature-related sensors, such as pressure or other voltage output sensors.

LTC2986 temperature measurement IC. Source: Linear Technology   LTC2986 temperature measurement IC. Source: Linear Technology The LTC2986’s high-performance analog front-end combines low noise and low offset buffered ADCs with all the necessary excitation and control circuits for each sensor. Measurements are performed under the control of a digital engine, combining all the algorithms and linearization required for each. The device precisely measures absolute microvolt-level signals from thermocouples, and ratiometric resistance measurements from RTDs and thermistors. It also performs the linearization and outputs the results in Celsius or Fahrenheit.

Up to ten analog inputs are available, allowing support for up to nine thermocouples, four RTDs, four thermistors and/or ten diodes. The SPI interface works with virtually any digital system, and a comprehensive software support system with drop-down menus allows easy customization of the LTC2986.

The LTC2986 interfaces with various temperature sensors, including type B, E, J, K, N, S, R, T thermocouples, two-, three- or four-wire RTDs, 2.25k Ω to 30k Ω thermistors and temperature-sensing diodes. The LTC2986 works with ground-referenced sensors without the need of amplifiers, negative supplies or level shift circuitry. Signals are simultaneously digitized with three high-accuracy, 24-bit Δ∑ ADCs using an internal 15ppm/°C reference. Automatic thermocouple cold junction compensation is accomplished using any type of external sensor. Included on the chip are linearization algorithms for all common sensor types.

Custom sensors can be linearized with custom coefficients, programmed and stored in the chip. Onboard EEPROM (LTC2986-1) is used to store user configuration data and custom sensor coefficients, 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.

To ensure resistive measurements are accurate, 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.

The LTC2986 comes in commercial, industrial and automotive versions, supporting operating temperature ranges from 0° C to 70° C, –40° C to 85° C and –40° C to 125° C, respectively. The part comes in an RoHS-compliant, 7 mm x 7 mm LQFP-48 package, and is pin-compatible with the LTC2983 and LTC2984. Pricing starts at $16.56 each in 1,000- piece quantities.

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