MAX31856 Precision Thermocople to Diital Conerter ith ...

1 general DescriptionThe MAX31856 performs cold-junction compensation and digitizes the signal from any type of thermocouple . The output data is formatted in degrees Celsius. This converter resolves temperatures to C, allows readings as high as +1800 C and as low as -210 C (depending on thermocouple type), and exhibits thermo-couple voltage measurement accuracy of The thermocouple inputs are protected against overvoltage conditions up to lookup table (LUT) stores linearity correction data for several types of thermocouples (K, J, N, R, S, T, E, and B). Line frequency filtering of 50Hz and 60Hz is included, as is thermocouple fault detection.

2 A SPI-compatible inter-face allows selection of thermocouple type and setup of the conversion and fault detection Temperature Controllers Industrial Ovens, Furnaces, and Environmental Chambers Industrial EquipmentBenefits and Features Provides High-Accuracy thermocouple Temperature Readings Includes Automatic Linearization Correction for 8 thermocouple Types (max, -20 C to +85 C) thermocouple Full-Scale and Linearity Error 19-Bit, C thermocouple Temperature Resolution Internal Cold-Junction Compensation Minimizes System Components C (max, -20 C to +85 C) Cold-Junction Accuracy 45V Input Protection Provides Robust System Performance Simplifies System Fault Management and Troubleshooting Detects Open Thermocouples Over- and Undertemperature Fault Detection 50Hz/60Hz Noise Rejection Filtering Improves System Performance 14-Pin TSSOP Package Ordering Information appears at end of data ; Rev 0; 2/15T-T+ MICROCONTROLLERMAX31856 Precision thermocouple to Digital Converter with LinearizationTypical Application CircuitEVALUATION KIT AVAILABLEAVDD, to + +, T-, Bias.

3 45VT+, T-, Bias .. 20mAAll Other Pins .. to (VDVDD + )Continuous Power Dissipation (TA = +70 C) TSSOP (derate C above +70 C) .. Protection (All pins, Human Body Model) ..2000 VOperating Temperature Range ..-55 C to +125 CJunction Temperature ..+150 CStorage Temperature Range ..-65 C to +150 CLead Temperature (soldering, 10s) ..+300 CSoldering Temperature (reflow) ..See IPC/JEDEC J-STD-020A SpecificationTSSOP Junction-to-Ambient Thermal Resistance ( JA) ..110 C/W Junction-to-Case Thermal Resistance ( JC) ..30 C/W(Note 1)( VDD , TA = -55 C to +125 C, unless otherwise noted.)(Notes 2, 3, and 4)Recommended DC Operating ConditionsElectrical Characteristics(TA = -55 C to +125 C, unless otherwise noted.)

4 (Notes 2 and 4)PARAMETER SYMBOL CONDITIONS MINTYP MAX UNITS Power-Supply VoltageVAVDD, +100mVCable ResistanceRCABLEPer lead40k Input Logic 0 Logic 1 SYMBOL CONDITIONS MINTYP MAX UNITS Supply AActive Temperature CCold-Junction Temperature Data Resolution CThermocouple Input Bias CurrentITCBIASTA = +25 C-10+10nATA = -40 C to +85 C-10+65TA = -55 C to +105 C-20+110TA = -55 C to +125 C-20+400 MAX31856 Precision thermocouple to Digital Converter with Integrated 2 Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-layer board. For detailed information on package thermal considerations, refer to Maximum RatingsStresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device.

5 These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device Thermal Characteristics( VDD , TA = -55 C to +125 C, unless otherwise noted.)(Notes 2, 3, and 4)PARAMETER SYMBOL CONDITIONS MINTYP MAX UNITS thermocouple Input Differential Bias Current (Note 4)ITCIDBIASTA = +25 C = -40 C to +85 C-4+4TA = -55 C to +105 + = -55 C to +125 C-10+10 Input-Referred NoiseVNAV = VRMSAV = RejectionPSRCold-junction C/VPower-On-Reset Voltage Voltage Output ResistanceRBIAS2k Input Common-Mode and INL Error (Note 6)TA = +25 + = -20 C to +85 + = -40 C to +105 + = -40 C to +125 + = -55 C to +125 + Offset Voltage (Note 7)

6 TA = +25 + = -20 C to +85 + = -40 C to +105 + = -55 C to +125 + Offset VoltageAV = 8TA = +25 + VTA = -20 C to +85 + = -40 C to +105 + = -55 C to +125 + = 32TA = +25 + = -20 C to +85 + = -40 C to +105 + = -55 C to +125 + Temperature ErrorTA = -20 C to +85 + CTA = -40 C to +105 C-1+1TA = -55 C to +125 C-2+2 Overvoltage Rising Threshold (Note 8)VAVDD + + thermocouple to Digital Converter with Integrated 3 Electrical Characteristics (continued)( VDD , TA = -55 C to +125 C, unless otherwise noted.)(Notes 2, 3, and 4)PARAMETER SYMBOL CONDITIONS MINTYP MAX UNITS Undervoltage Falling Edge Threshold (Note 8) Linearity Correction ErrorType B,TA = 0 to 125 C, TTC = 95 C to +1798 + CType E, TA = -55 C to +125 CTTC = -200 C to +1000 + J, TA = -55 C to +125 CTTC = -210 C to +1200 + K, TA = -55 C to +125 CTTC = -200 C to +1372 + N, TA = -55 C to +125 CTTC = -200 C to +1300 + R, TA = -50 C to +125 CTTC = -50 C to +1768 + S, TA = -50 C to +125 CTTC = -50 C to +1768 + T, TA = -55 C to +125 CTTC = -200 C to +400 + Conversion Time ( thermocouple + Cold Junction)tCONV1-Shot conversion or first conversion in auto-conversion mode (60Hz)

7 143155ms1-Shot conversion or first conversion in auto-conversion mode (50Hz)169185 Auto conversion mode, conversions 2 through n (60Hz) 8290 Auto conversion mode, conversions 2 through n (50Hz) 98110 MAX31856 Precision thermocouple to Digital Converter with Integrated 4 Electrical Characteristics (continued)Note 2: All voltages are referenced to GND. Currents entering the IC are specified positive, and currents exiting the IC are negative. Note 3: All Serial Interface timing specifications are guaranteed by 4: Specification is 100% tested at TA = +25 C. Specification limits over temperature (TA = TMIN to TMAX) are guaranteed by design and characterization; not production 5: For all pins except T+ and T- (see the thermocouple Input Bias Current parameter in the Electrical Characteristics 6: Using a common-mode voltage other than VBIAS will change this specification.)

8 See the Typical Operating Characteristics for 7: Input-referred full-scale voltage is when AV = 8 and is when AV = 8: Overvoltage and undervoltage limits apply to T+, T-, and BIAS pins. ( VDD , TA = -55 C to +125 C, unless otherwise noted.)(Notes 2, 3, and 4)PARAMETER SYMBOL CONDITIONS MINTYP MAX UNITS Common-Mode VCM Noise RejectionFundamental and harmonics91dBSERIAL INTERFACEI nput Leakage CurrentILEAK(Note 5)-1+1 AOutput High VoltageVOHIOUT = - Low VoltageVOLIOUT = CapacitanceCIN8pFSerial Clock FrequencyfSCL5 MHzSCK Pulse High WidthtCH100nsSCK Pulse Low WidthtCL100nsSCK Rise and Fall TimetR, tFCL = 10pF200nsCS Fall to SCK RisetCCCL = 10pF100nsSCK to CS HoldtCCHCL = 10pF100nsCS Rise to Output DisabletCDZCL = 10pF40nsData to SCLK SetuptDC35nsSCLK to Data HoldtCDH35nsSCK Fall to Output Data ValidtCDDCL = 10pF80nsCS Inactive TimetCWH(Note 3)

9 400nsMAX31856 Precision thermocouple to Digital Converter with Integrated 5 Electrical Characteristics (continued)Figure 1. Timing Diagram: SPI Read Data TransferFigure 2. Timing Diagram: SPI Write Data TransferCSSCLKSDISDOtCCtCDHA7A6A0D7D6D1D 0tDCtCDDtCDDtCDZNOTE: SCLK CAN BE EITHER POLARITY, TIMING SHOWN FOR CPOL = ADDRESS BYTEREAD DATA BYTESCLKSDINOTE: SCLK CAN BE EITHER POLARITY, TIMING SHOWN FOR CPOL = ADDRESS BYTEWRITE DATA BYTEtCCtCDHtCHtRtFtCCHtCWHtCDHA7A6A0D7D0 tDCtCLCSMAX31856 Precision thermocouple to Digital Converter with Integrated 6(VCC = and TA = +25 C, unless otherwise noted.) CURRENT (mA)TEMPERATURE( C)ACTIVE SUPPLY CURRENT vs. TEMPERATUREtoc01 VDD= CURRENT ( A)TEMPERATURE( C)STANDBY SUPPLY CURRENT vs.

10 TEMPERATUREtoc02 VDD= BIAS CURRENT (nA)TEMPERATURE( C) thermocouple INPUT BIAS CURRENT vs. TEMPERATUREtoc03 VDD= , , BIAS CURRENT (nA)TEMPERATURE( C) thermocouple INPUT DIFFERENTIAL BIAS CURRENT vs. TEMPERATUREtoc04 VDD= , , Input Voltage = 0V-1012345-55-35-15525456585105125 DIFFERENTIAL BIAS CURRENT (nA)TEMPERATURE( C) thermocouple INPUT DIFFERENTIAL BIAS CURRENT vs. TEMPERATUREtoc05 Differential Input Voltage = ERROR (%)TEMPERATURE( C)AV = 8 FULL-SCALE ERRORvs. TEMPERATUREtoc06 VDD= ERROR (%)TEMPERATURE( C)AV = 32 FULL-SCALE ERRORvs. TEMPERATUREtoc07 VDD= thermocouple to Digital Converter with LinearizationMaxim Integrated Operating Characteristics(VCC = and TA = +25 C, unless otherwise noted.)