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MAX31850/MAX31851

Cold-Junction Compensated, 1-Wire

Thermocouple-to-Digital Converters

General Description

The MAX31850/MAX31851 cold-junction compensat-

ed, 1-Wire

thermocouple-to-digital converters perform

cold-junction compensation and digitize the signal from

a K-, J-, N-, T-, S-, R-, or E-type thermocouple. The con-

verters resolve temperatures to 0.25NC, allow readings

as high as +1768NC and as low as -270NC, and exhibit

thermocouple accuracy of 8 LSBs (2NC) for temperatures

ranging from -200NC to +700NC.

Communication with the master microcontroller is over a

1-Wire bus that by definition requires only one data line

(and ground) for communication. Operating power can

be obtained directly from the data line (“parasite power”),

eliminating the need for an external power supply.

Each device has a unique 64-bit serial code, which

allows multiple units to function on the same 1-Wire bus.

Therefore, it is simple to use one microcontroller (the

master device) to monitor temperature from many ther-

mocouples distributed over a large area.

Four location address inputs simplify mapping of

individual units to specific locations.

Benefits and Features

S Integration Reduces Design Time and Lowers

System Cost

• 14-Bit, 0.25NC Resolution

• Integrated Cold-Junction Compensation

• Available for Multiple Thermocouples Types:

Supports K-, J-, N-, T-, and E-Type (MAX31850);

S- and R-Type (MAX31851)

• Detects Thermocouple Shorts to GND or V

• Detects Open Thermocouple

S 1-Wire Multiddrop Capability Simplifies

Multisensor Systems

• 1-Wire Interface (Read-Only); Power Can Be

Obtained from Interface (Parasite-Powered Mode)

Applications

Industrial

Appliances

HVAC

Medical

Block Diagram

19-6725; Rev 2; 1/15

Ordering Information appears at end of data sheet.

1-Wire is a registered trademark of Maxim Integrated Products, Inc.

For related parts and recommended products to use with this part, refer to: www.maximintegrated.com/MAX31850.related

EVALUATION KIT AVAILABLE

MAX31850

MAX31851

64-BIT ROM

AND

1-Wire PORT

ADC

PARASITE-

POWER

CIRCUIT

GND

MEMORY

CONTROL LOGIC

COLD-JUNCTION

COMPENSATION

FAULT

DETECTION

REFERENCE

VOLTAGE

POWER-

SUPPLY

SENSE

ADDRESS PIN INPUT

AD0 AD1 AD2 AD3

SCRATCHPAD

T+

T-

For pricing, delivery, and ordering information, please contact Maxim Direct at

1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.

Summary of content (25 pages)

PAGE 1
EVALUATION KIT AVAILABLE MAX31850/MAX31851 Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converters General Description Benefits and Features The MAX31850/MAX31851 cold-junction compensated, 1-WireM thermocouple-to-digital converters perform cold-junction compensation and digitize the signal from a K-, J-, N-, T-, S-, R-, or E-type thermocouple. The converters resolve temperatures to 0.
PAGE 2
MAX31850/MAX31851 Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converters ABSOLUTE MAXIMUM RATINGS Supply Voltage Range (VDD to GND)...................-0.3V to +4.0V All Other Pins............................................. -0.3V to (VDD + 0.3V) Continuous Power Dissipation (TA = +70NC) TDFN (derate 16.70mW/NC above +70NC)............1333.30mW ESD Protection (All Pins, Human Body Model)....................±2kV Operating Temperature Range.........................
PAGE 3
MAX31850/MAX31851 Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converters THERMAL CHARACTERISTICS (3.0V P VDD P 3.6V, TA = -40NC to +125NC, unless otherwise noted.) (Note 2) PARAMETER MAX31850K Thermocouple Temperature Gain and Offset Error (41.276FV/NC nominal sensitivity) (Note 11) MAX31850J Thermocouple Temperature Gain and Offset Error (57.953FV/NC nominal sensitivity) (Note 11) MAX31850N Thermocouple Temperature Gain and Offset Error (36.
PAGE 4
MAX31850/MAX31851 Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converters THERMAL CHARACTERISTICS (continued) (3.0V P VDD P 3.6V, TA = -40NC to +125NC, unless otherwise noted.) (Note 2) PARAMETER SYMBOL MAX31851R Thermocouple Temperature Gain and Offset Error (10.506FV/NC nominal sensitivity) (Note 11) MAX31851S Thermocouple Temperature Gain and Offset Error (9.
PAGE 5
MAX31850/MAX31851 Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converters 1-Wire TIMING CHARACTERISTICS (3.0V P VDD P 3.6V, TA = -40NC to +125NC, unless otherwise noted.
PAGE 6
MAX31850/MAX31851 Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converters 1-Wire Timing Diagrams 1-Wire WRITE-ZERO TIME SLOT START OF NEXT CYCLE tSLOT tREC tLOW0 1-Wire READ-ZERO TIME SLOT tSLOT START OF NEXT CYCLE tREC tRDV 1-Wire RESET PULSE RESET PULSE FROM HOST tRSTL tRSTH 1-Wire PRESENCE DETECT PRESENCE DETECT tPDHIGH tPDLOW Maxim Integrated 6
PAGE 7
MAX31850/MAX31851 Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converters Typical Operating Characteristics (VCC = +3.3V, TA = +25NC, unless otherwise noted.) 800 600 400 200 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0 20 40 60 80 -40 -20 100 120 0 20 40 60 80 -0.2 -40 -20 TA = +125°C TA = -40°C 0.5 TA = +85°C 0 0 20 40 60 80 100 120 TEMPERATURE (°C) 0.20 INTERNAL TEMPERATURE = +25°C 0.15 0.10 ADC ACCURACY (°C) ADC ACCURACY (°C) -0.1 ADC ACCURACY vs.
PAGE 8
MAX31850/MAX31851 Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converters Pin Configuration TOP VIEW DNC AD3 AD2 AD1 AD0 10 9 8 7 6 MAX31850 MAX31851 EP + 1 2 3 4 5 GND T- T+ VDD DQ TDFN-EP (3mm x 4mm) Pin Description PIN NAME 1 GND 2 T- Thermocouple Input. See Table 1. Do not connect to GND. 3 T+ Thermocouple Input. See Table 1. 4 VDD Power-Supply Voltage 5 DQ Data Input/Output. Open-drain 1-Wire interface pin.
PAGE 9
MAX31850/MAX31851 Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converters Detailed Description the introduction of noise errors from the thermocouple wires. The MAX31850/MAX31851 are sophisticated thermocouple-to-digital converters with a built-in 14-bit analogto-digital converter (ADC), cold-junction compensation sensing and correction, a digital controller, a 1-Wire data interface, and associated control logic.
PAGE 10
MAX31850/MAX31851 Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converters Table 1. Thermocouple Wire Connections and Nominal Sensitivities TYPE T- WIRE T+ WIRE TEMP RANGE (°C) SENSITIVITY (µV/°C) COLD-JUNCTION SENSITIVITY (µV/°C) (0NC TO +70NC) K Alumel Chromel -270 to +1372 41.276 (0NC to +1000NC) 40.73 J Constantan Iron -210 to +1200 57.953 (0NC to +750NC) 52.136 N Nisil Nicrosil -270 to +1300 36.256 (0NC to +1000NC) 27.
PAGE 11
MAX31850/MAX31851 Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converters VPU MAX31850 MAX31851 GND VPU µP DQ VDD 4.7kΩ 1-Wire BUS TO OTHER 1-Wire DEVICES Figure 1. Supplying the Parasite-Powered MAX31850/MAX31851 During Temperature Conversions MAX31850 MAX31851 GND VPU µP DQ VDD (EXTERNAL SUPPLY) VDD 4.7kΩ 1-Wire BUS TO OTHER 1-Wire DEVICES Figure 2.
PAGE 12
MAX31850/MAX31851 Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converters MSb LSb 8-BIT CRC CODE MSb 8-BIT FAMILY CODE (3Bh) 48-BIT SERIAL NUMBER LSb MSb LSb MSb LSb Figure 3.
PAGE 13
MAX31850/MAX31851 Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converters Configuration Register Byte 4 of Scratchpad contains the configuration register, which is organized as shown in Configuration Register Format. The configuration register allows the user to read the programmed value of the address pins. The AD[3:0] bits report the pin-programmed location information. Pins connected to DQ are reported with logic 1, and pins connected to GND are reported as logic 0.
PAGE 14
MAX31850/MAX31851 Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converters CRC Generation shift register. After shifting in the 56th bit from the ROM or the most significant bit of byte 7 from the scratchpad, the polynomial generator contains the recalculated CRC. Next, the 8-bit ROM code or scratchpad CRC from the device must be shifted into the circuit. At this point, if the recalculated CRC was correct, the shift register contains all zeros.
PAGE 15
MAX31850/MAX31851 Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converters VPU BUS MASTER MAX31850/MAX31851 1-Wire PORT 4.7kΩ DQ Rx Tx Rx = RECEIVE Tx = TRANSMIT OPEN-DRAIN PORT PIN Rx 5µA TYP Tx 100Ω MOSFET Figure 6. Hardware Configuration The 1-Wire bus requires an external pullup resistor of approximately 5kI; thus, the idle state for the 1-Wire bus is high. If for any reason a transaction needs to be suspended, the bus must be left in the idle state if the transaction is to resume.
PAGE 16
MAX31850/MAX31851 Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converters Read ROM [33h] This command can be used only when there is one slave on the bus. It allows the bus master to read the slave’s 64-bit ROM code without using the Search ROM command procedure. If this command is used when there is more than one slave present on the bus, a data collision occurs when all the slaves attempt to respond at the same time.
PAGE 17
MAX31850/MAX31851 Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converters MASTER Tx RESET PULSE INITIALIZATION SEQUENCE DEVICE Tx PRESENCE PULSE MASTER Tx ROM COMMAND 33h READ ROM? Y N 55h MATCH ROM? F0h SEARCH ROM? N Y Y DEVICE Tx SERIAL NUMBER 6 BYTES DEVICE Tx CRC BYTE N Y DEVICE Tx BIT 0 MASTER Tx BIT 0 N N BIT 0 MATCH? Y DEVICE Tx FAMILY CODE 1 BYTE CCh SKIP ROM? DEVICE Tx BIT 0 MASTER Tx BIT 0 BIT 0 MATCH? N Y DEVICE Tx BIT 1 MASTER Tx BIT 1 BIT 1 MATCH? DEVICE Tx
PAGE 18
MAX31850/MAX31851 Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converters 44h CONVERT T? MASTER Tx FUNCTION COMMAND N Y N DEVICE BEGINS CONVERSION MASTER ENABLES STRONG PULLUP ON DQ DEVICE CONVERTING TEMPERATURE? DEVICE CONVERTS TEMPERATURE N Y MASTER Rx “0s” N Y PARASITE POWER? MASTER Rx “1s” B4h READ POWER SUPPLY? MASTER DISABLES STRONG PULLUP N Y N MASTER Rx “1s” PARASITE POWER? BEh READ SCRATCHPAD? Y Y MASTER Rx “0s” MASTER Rx DATA BYTE FROM SCRATCHPAD MASTER Tx RE
PAGE 19
MAX31850/MAX31851 Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converters SEARCH ALL ROM IDs ON BUS AND STORE ROM IDs (F0h COMMAND) INCREMENT COUNTER N=N+1 N > NMAX? N BUILDING CROSS-REFERENCE TABLE USING ROM IDs AND 4-BIT ADDRESSES Y DONE NMAX IS THE NUMBER OF ROM IDs FOUND MASTER Tx NEXT ROM ID READ SCRATCHPAD (USE AD3−AD0 FROM CONFIG REGISTER) MATCH ROM ID TO ADDRESS AND ADD TO CROSS-REFERENCE TABLE CROSS-REFERENCE TABLE ROM ID ROM ID(0) ROM ID(1) ROM ID(2) ROM ID(3) AD3−AD0 0000 00
PAGE 20
MAX31850/MAX31851 Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converters MASTER Tx RESET PULSE 480µs MINIMUM VPU MAX31850/MAX31851 WAITS 15µs TO 60µs MASTER Rx 480µs MINIMUM MAX31850/MAX31851 Tx PRESENCE PULSE 60µs TO 240µs 1-Wire BUS GND BUS MASTER PULLING LOW MAX31850/MAX31851 PULLING LOW RESISTOR PULLUP Figure 10. Initialization Timing and then transmits a presence pulse by pulling the 1-Wire bus low for 60Fs to 240Fs.
PAGE 21
MAX31850/MAX31851 Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converters START OF SLOT START OF SLOT MASTER WRITE-ONE SLOT MASTER WRITE-ZERO SLOT 1µs < tREC < ∞ 60µs < Tx “0” < 120µs > 1µs VPU 1-Wire BUS GND MAX31850/MAX31851 SAMPLES MAX31850/MAX31851 SAMPLES MIN 15µs TYP 15µs MIN MAX 30µs 15µs MASTER READ-ZERO SLOT TYP 15µs MAX 30µs MASTER READ-ONE SLOT 1µs < tREC < ∞ VPU 1-Wire BUS GND MASTER SAMPLES > 1µs MASTER SAMPLES > 1µs 15µs 45µs BUS MASTER PULLING LOW 15µs MA
PAGE 22
MAX31850/MAX31851 Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converters VPU VIH OF MASTER 1-Wire BUS GND tINIT = SMALL MASTER SAMPLES tRC = SMALL 15µs BUS MASTER PULLING LOW RESISTOR PULLUP Figure 13. Recommended Master Read-One Timing Table 6. Operation Example MASTER MODE DATA (LSB FIRST) Tx Reset Rx Presence Devices respond with presence pulse.
PAGE 23
MAX31850/MAX31851 Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converters 1-Wire BUS AD0 DQ VDD VDD MAX31850 MAX31851 AD1 AD2 GND AD3 DQ AD0 LOCATION 0 AD0 = GND AD1 = GND AD2 = GND AD3 = GND 1-Wire BUS AD0 DQ VDD MAX31850 MAX31851 AD1 AD2 GND AD3 DQ AD0 LOCATION 0 AD0 = GND AD1 = GND AD2 = GND AD3 = GND VDD VDD MAX31850 MAX31851 AD1 AD2 GND AD3 DQ AD0 LOCATION 1 AD0 = VDD AD1 = GND AD2 = GND AD3 = GND VDD MAX31850 MAX31851 AD1 AD2 GND AD3 DQ AD0 LOCATION 1
PAGE 24
MAX31850/MAX31851 Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converters Thermal Considerations Self-heating degrades the temperature measurement accuracy of the MAX31850/MAX31851 in some applications. The magnitude of the temperature errors depends on the thermal conductivity of the MAX31850/ MAX31851 package, the mounting technique, and the effects of airflow. Use a large ground plane to improve the temperature measurement accuracy of the MAX31850/ MAX31851.
PAGE 25
MAX31850/MAX31851 Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converters Revision History REVISION NUMBER REVISION DATE 0 6/13 Initial release 1 8/13 Clarify that MAX31850 can be used for R- and S- thermocouples 2 1/15 Revised the Benefits and Features section DESCRIPTION PAGES CHANGED — 1, 4, 11, 16, 24 1 Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product.