LTM2985 Isolated High Accuracy Digital Temperature Measurement System with EEPROM FEATURES DESCRIPTION n 5000V Isolated Power and SPI Interface The LTM 2985 measures a wide variety of temperature RMS n Directly Digitizes 2-, 3- or 4-Wire RTDs, sensors and digitally outputs the result, in C or F, with Thermocouples, Thermistors and Diodes 0.1C accuracy and 0.001C resolution. The LTM2985 can n 10 Flexible Inputs Allow Interchanging Sensors measure the temperature of virtually all standard (Type B, n Automatic Thermocouple Cold Junction Compensation E, J, K, N, S, R, T) or custom thermocouples, automatically n Built-In Standard and User-Programmable Coefficients compensate for cold junction temperatures and linearize for Thermocouples, RTDs and Thermistors the results. The device can also measure temperature n Automatic Burn Out, Short-Circuit and Fault Detection with standard 2-, 3- or 4-wire RTDs, thermistors and n Buffered Inputs Allow External Protection diodes. The LTM2985 includes excitation current sources n Simultaneous 50Hz/60Hz Rejection and fault detection circuitry appropriate for each type of n Includes 15ppm/C (Max) Reference temperature sensor. n Includes Special Protection Modes The LTM2985 is an isolated 10-channel temperature mea- n On-Chip EEPROM Stores Channel Configuration Data surement system software compatible with the LTC2986-1. and Custom Coefficients It provides 5kV isolated power and SPI interface to the precision temperature-to-bits converter. The LTM2985 APPLICATIONS also includes a user-programmable EEPROM for custom n sensor data. Direct Thermocouple Measurements All registered trademarks and trademarks are the property of their respective owners. n Direct RTD Measurements PatentsPending n Direct Thermistor Measurements n Custom Sensor Applications TYPICAL APPLICATION Typical Temperature Error Universal Isolated Temperature Measurement System Contribution 0.5 LTM2985 CH1 THER- THER- 2-WIRE 3-WIRE 4-WIRE 0.4 R MOCOUPLE MISTOR RTD RTD RTD SENSE 4.5V RP1 CH2 0.3 V TO CC THERMISTOR 3 4 5.5V RP2 2 2 3 0.2 THERMOCOUPLE CH3 V L RP3 0.1 CH4 ON RP4 0 2 CH5 CS 1 1 0.1 RP5 1 CH6 SDI 0.2 3904 DIODE SPI RP7 RTD CH7 SDO 0.3 RP8 RP6 SCK CH8 0.4 COLD JUNCTION CH9 0.5 RTD OR 200 0 200 400 600 800 1000 1200 1400 CH10 THERMISTOR OR TEMPERATURE (C) DIODE OR COM 2985 TA01b ANALOG TEMP GND2 GND 29861 TA02 2985 TA01a Rev. 0 1 Document Feedback For more information www.analog.com 5kV ISOLATION BARRIER ERROR (C)LTM2985 TABLE OF CONTENTS Features ............................................................................................................................ 1 Applications ....................................................................................................................... 1 Typical Application ............................................................................................................... 1 Description......................................................................................................................... 1 Absolute Maximum Ratings ..................................................................................................... 3 Order Information ................................................................................................................. 3 Pin Configuration ................................................................................................................. 3 Complete System Electrical Characteristics .................................................................................. 4 ADC Electrical Characteristics .................................................................................................. 5 Reference Electrical Characteristics ........................................................................................... 5 Digital Inputs and Digital Outputs .............................................................................................. 6 Isolation Characteristics ......................................................................................................... 6 LTM2985 EEPROM Characteristics ............................................................................................. 7 Typical Performance Characteristics .......................................................................................... 8 Pin Functions .....................................................................................................................11 Block Diagram ....................................................................................................................12 Test Circuits ......................................................................................................................13 Timing Diagram ..................................................................................................................13 Overview ..........................................................................................................................14 Applications Information .......................................................................................................18 EEPROM Overview................................................................................................................................................ 24 EEPROM Read/Write Validation ............................................................................................................................ 24 EEPROM Write Operation ..................................................................................................................................... 24 EEPROM Read Operation ...................................................................................................................................... 25 Thermocouple Measurements .............................................................................................................................. 26 Diode Measurements ............................................................................................................................................ 29 RTD Measurements .............................................................................................................................................. 33 Thermistor Measurements .................................................................................................................................... 52 Global Configuration Register ............................................................................................................................... 61 Input Overvoltage Protection Overview.............................................................................................................. 61 Active Analog Temperature Sensors ..................................................................................................................... 67 Direct ADC Measurements .................................................................................................................................... 71 Supplemental Information ......................................................................................................76 2- and 3-Cycle Conversion Modes ........................................................................................................................ 76 Running Conversions Consecutively on Multiple Channels ................................................................................... 76 Entering/Exiting Sleep Mode ................................................................................................................................. 77 MUX Configuration Delay ...................................................................................................................................... 77 Reference Considerations ..................................................................................................................................... 77 Custom Thermocouples .........................................................................................................78 Custom RTDs .....................................................................................................................81 Custom Thermistors .............................................................................................................84 Package Description ............................................................................................................89 Typical Application ..............................................................................................................90 Related Parts .....................................................................................................................90 Rev. 0 2 For more information www.analog.com