Thermocouple Amplifier MAX31855 breakout board (MAX6675 upgrade) PRODUCT ID: 269 9/30/2014
DESCRIPTION Thermocouples are very sensitive, requiring a good amplifier with a cold-compensation reference. The MAX31855K does everything for you, and can be easily interfaced with any microcontroller, even one without an analog input. This breakout board has the chip itself, a 3.3V regulator with 10uF bypass capacitors and level shifting circuitry, all assembled and tested. Comes with a 2 pin terminal block (for connecting to the thermocouple) and pin header (to plug into any breadboard or perfboard).
19-5793; Rev 2; 2/12 MAX31855 Cold-Junction Compensated Thermocouple-to-Digital Converter General Description The MAX31855 performs cold-junction compensation and digitizes the signal from a K-, J-, N-, T-, S-, R-, or E-type thermocouple. The data is output in a signed 14-bit, SPI-compatible, read-only format. This converter resolves temperatures to 0.
MAX31855 Cold-Junction Compensated Thermocouple-to-Digital Converter ABSOLUTE MAXIMUM RATINGS Supply Voltage Range (VCC to GND)...................-0.3V to +4.0V All Other Pins............................................. -0.3V to (VCC + 0.3V) Continuous Power Dissipation (TA = +70NC) SO (derate 5.9mW/NC above +70NC)........................470.6mW ESD Protection (All Pins, Human Body Model)....................±2kV Operating Temperature Range......................... -40NC to +125NC Junction Temperature.....
MAX31855 Cold-Junction Compensated Thermocouple-to-Digital Converter THERMAL CHARACTERISTICS (3.0V P VCC P 3.6V, TA = -40NC to +125NC, unless otherwise noted.) (Note 4) PARAMETER MAX31855K Thermocouple Temperature Gain and Offset Error (41.276FV/NC nominal sensitivity) (Note 4) MAX31855J Thermocouple Temperature Gain and Offset Error (57.953FV/NC nominal sensitivity) (Note 4) MAX31855N Thermocouple Temperature Gain and Offset Error (36.
MAX31855 Cold-Junction Compensated Thermocouple-to-Digital Converter THERMAL CHARACTERISTICS (continued) (3.0V P VCC P 3.6V, TA = -40NC to +125NC, unless otherwise noted.) (Note 4) PARAMETER SYMBOL CONDITIONS MIN Thermocouple Temperature Data Resolution Cold-Junction Temperature Data Resolution Thermocouple Conversion Power-Up Time MAX 0.
MAX31855 Cold-Junction Compensated Thermocouple-to-Digital Converter Serial-Interface Diagrams CS SCK SO D31 D8 D7 D6 D5 D4 D2 D3 D1 D0 Figure 1. Serial-Interface Protocol tCSS CS tCH tCL SCK tDV tDO tTR SO D31 D3 D2 D1 D0 Figure 2.
MAX31855 Cold-Junction Compensated Thermocouple-to-Digital Converter Typical Operating Characteristics (VCC = +3.3V, TA = +25NC, unless otherwise noted.) 1.0 VCC = 3.3V 0.8 VCC = 3.0V 0.6 0.4 0.7 0.2 0.5 0.4 NOTE: THIS DATA WAS TAKEN IN PRECISION BATH SO HIGH TEMPERATURE LIMIT IS 90°C 0.3 0.2 0.1 0 -0.1 0 -40 -20 0 20 40 60 80 -0.2 100 120 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) ADC ACCURACY vs. ADC INPUT VOLTAGE ACROSS TEMPERATURE ADC ACCURACY vs.
MAX31855 Cold-Junction Compensated Thermocouple-to-Digital Converter Pin Description Pin Configuration TOP VIEW T- 2 T+ MAX31855 3 1 GND FUNCTION Ground 2 T- 8 DNC 3 T+ Thermocouple Input. See Table 1. 7 SO 4 VCC Power-Supply Voltage 5 SCK Serial-Clock Input 6 CS Active-Low Chip Select. Set CS low to enable the serial interface. 7 SO Serial-Data Output 8 DNC 6 VCC 4 NAME Thermocouple Input. See Table 1. Do not connect to GND.
MAX31855 Cold-Junction Compensated Thermocouple-to-Digital Converter Detailed Description The MAX31855 is a sophisticated thermocouple-todigital converter with a built-in 14-bit analog-to-digital converter (ADC). The device also contains cold-junction compensation sensing and correction, a digital controller, an SPI-compatible interface, and associated control logic.
MAX31855 Cold-Junction Compensated Thermocouple-to-Digital Converter the same temperature as the board on which the device is mounted) can range from -55NC to +125NC. While the temperature at the cold end fluctuates, the device continues to accurately sense the temperature difference at the opposite end. The device senses and corrects for the changes in the reference junction temperature with cold-junction compensation.
MAX31855 Cold-Junction Compensated Thermocouple-to-Digital Converter Table 2. Memory Map—Bit Weights and Functions 14-BIT THERMOCOUPLE RES TEMPERATURE DATA D31 BIT VALUE D30 Sign … MSB 210 (1024NC) … D18 LSB 2-2 (0.25NC) D17 Reserved FAULT 12-BIT INTERNAL TEMPERATURE BIT DATA D16 1= Fault D15 D14 … MSB 26 Sign … (64NC) D4 LSB 2-4 (0.0625NC) RES D3 Reserved SCV SCG OC BIT BIT BIT D2 D1 D0 1= 1= Short Short to to VCC GND 1= Open Circuit Table 3.
MAX31855 Cold-Junction Compensated Thermocouple-to-Digital Converter Applications Information The thermocouple system’s accuracy can also be improved by following these precautions: Noise Considerations • Use the largest wire possible that does not shunt heat away from the measurement area. Because of the small signal levels involved, thermocouple temperature measurement is susceptible to powersupply coupled noise. The effects of power-supply noise can be minimized by placing a 0.
MAX31855 Cold-Junction Compensated Thermocouple-to-Digital Converter Ordering Information PART THERMOCOUPLE TYPE MEASURED TEMP RANGE PIN-PACKAGE MAX31855KASA+ K -200NC to +1350NC 8 SO MAX31855KASA+T K -200NC to +1350NC 8 SO MAX31855JASA+ J -40NC to +750NC 8 SO MAX31855JASA+T J -40NC to +750NC 8 SO MAX31855NASA+ N -200NC to + 1300NC 8 SO MAX31855NASA+T N -200NC to + 1300NC 8 SO MAX31855SASA+ S +50NC to +1600NC 8 SO MAX31855SASA+T S +50NC to +1600NC 8 SO MAX31855TASA+ T -
MAX31855 Cold-Junction Compensated Thermocouple-to-Digital Converter Revision History REVISION NUMBER REVISION DATE DESCRIPTION 0 3/11 Initial release 1 11/11 Corrected ESD protection value; added “S” and “R” type specifications 2/12 Corrected the thermocouple temperature conditions in the Thermal Characteristics table and Table 1; added clarification to the Serial Interface section to help users better understand how to communicate with the device; added a recommendation to add a 10nF differentia
