MAX31855KASA+ - K-Type Thermocouple-to-Digital Converter | Maxim Integrated
料号： MAX31855KASA+ ✓ 量产中| 数量 | 单价 | 小计 |
|---|---|---|
| 1 | $8.2 | $8.20 |
| 10 | $7.3 | $73.00 |
| 100 | $5.95 | $595.00 |
| 500 | $4.85 | $2,425.00 |
| 1,000 | $4.2 | $4,200.00 |
MAX31855KASA+ 概述
An integrated thermocouple-to-digital converter such as the MAX31855KASA+ belongs to the broader sensor signal-chain IC family, which sits hierarchically under temperature sensor ICs -> sensors -> analog/mixed-signal ICs -> semiconductors. By performing linearization and cold-junction compensation in hardware, the part eliminates firmware lookup tables for Seebeck-coefficient polynomial correction and lets microcontrollers consume temperature data directly over SPI, freeing CPU bandwidth for system-level tasks.
Key features of the MAX31855KASA+ include 14-bit signed output resolution (plus sign bit), an SPI read-only interface with up to 4.3 MHz clock, on-chip open-thermocouple detection that flags a fault bit when the probe breaks, and a 2.7 V to 3.6 V supply range. The 8-pin NSOIC package provides low thermal mass for accurate cold-junction measurement and supports hand-solderable prototyping as well as high-volume reflow assembly. A dedicated fault register reports open thermocouple, short-to-GND, and short-to-VDD conditions in addition to the temperature data.
Typical applications for the MAX31855KASA+ include industrial furnace and oven temperature monitoring, 3D-printer hot-end and bed thermistor replacement, HVAC duct sensing, automotive exhaust and engine-temperature logging, food-service and laboratory equipment, and any embedded design that previously used a MAX6675 and now needs higher resolution plus thermocouple open-detection. The wide -270 degC to +1800 degC supported span also makes it suitable for cryogenic instrumentation and high-temperature process control.
When designing with the MAX31855KASA+, keep the thermocouple traces short, matched, and physically separated from switching nodes to preserve common-mode noise immunity. Place the device close to the thermocouple connector so the on-chip cold-junction sensor tracks the cold-junction temperature accurately, and add a 0.1 uF decoupling capacitor close to VDD. Unlike the MAX6675 it replaces, the MAX31855 changes SPI framing and clock polarity, so existing firmware must be updated; it is not code-compatible with the legacy part.
直接替换替代料： MAX31855KASA+ ——相同封装，引脚兼容。需要 PCB 改动的不同封装料号已排除。
快速对比工具——选择替代料号进行并排对比：
MAX31855JASA+
✅ 直接替换📋 参考替代料（不在目录中）
MAX31855NASA+
✅ 直接替换📋 参考替代料（不在目录中）
MAX31855TASA+
✅ 直接替换📋 参考替代料（不在目录中）
MAX31855EASA+
✅ 直接替换📋 参考替代料（不在目录中）
MAX31855KASA+T
✅ 直接替换📋 参考替代料（不在目录中）
MAX31855KASA+ 最大额定值与电气特性
| 功能 | Thermocouple-to-Digital Converter with Cold-Junction Compensation |
| Supported Thermocouple Type | K (K-type probe input) |
| Output Resolution | 14-bit signed (0.25 degC per LSB) |
| Output Interface | SPI-compatible, read-only |
| Thermocouple Temperature Range | -270 degC to +1800 degC |
| Thermocouple Accuracy | plus/minus 2 degC |
| Cold-Junction Compensation | On-chip, integrated |
| Open-Thermocouple Detection | Yes (fault register) |
| Supply Voltage (VDD) | 3.0 V to 3.6 V (2.7 V min per datasheet) |
| 工作温度 | -40 degC to +125 degC |
| 封装 | 8-pin SOIC (NSOIC), 3.90 mm body |
| 安装类型 | Surface Mount |
| RoHS 状态 | Compliant (per distributor listing) |
MAX31855KASA+ 引脚配置
| 引脚 1 | GND — Ground reference for the IC and thermocouple inputs |
| 引脚 2 | T- — Thermocouple negative input (K-type chromel/alumel) |
| 引脚 3 | T+ — Thermocouple positive input (K-type chromel/alumel) |
| 引脚 4 | VDD — 3.0 V to 3.6 V supply input; decouple with 0.1 uF |
| 引脚 5 | SCK — SPI serial-clock input (active low, idles high) |
| 引脚 6 | CS — SPI chip-select input (active low) |
| 引脚 7 | SO — SPI serial-data output (tri-state when CS high) |
| 引脚 8 | NC — Not connected on K-variant datasheet pinout |
典型应用
MAX31855KASA+ 适用于 6 应用s: Industrial Furnace and Oven Monitoring, 3D Printer Hot-End and Heated Bed Sensing, HVAC Duct and Refrigeration Sensing, Automotive Exhaust and Engine Temperature Logging, Food Service and Laboratory Equipment, Cryogenic and High-Temperature Process Control.
Industrial Furnace and Oven Monitoring
The MAX31855KASA+ fits furnace and oven monitoring because its 14-bit signed output covers the -270 degC to +1800 degC K-type probe range that industrial Type-K mineral-insulated probes are spec'd for, and its plus/minus 2 degC accuracy is sufficient for kiln curve profiling, heat-treat recipes, and ceramic firing schedules. Placed within 2-3 cm of the Type-K screw terminal on the oven chassis so the on-chip cold-junction sensor tracks ambient accurately, the device drives a 3.3 V microcontroller over SPI at up to 4.3 MHz and reports open-thermocouple faults within one read cycle, which lets a PLC fail-safe rather than display a misleading mid-scale temperature. Unlike a discrete op-amp + ADC + software linearization chain, the MAX31855KASA+ integrates the Seebeck-coefficient polynomial in silicon and frees the MCU from per-sample floating-point math.
推荐
3D Printer Hot-End and Heated Bed Sensing
The MAX31855KASA+ is widely used in 3D-printer hot-end and heated-bed designs because the K-type thermocouple survives the 250-300 degC extrusion environment that thermistors cannot, and the device's SPI interface plugs directly into Marlin/Klipper firmware running on 3.3 V microcontrollers. Per the MAX31855 datasheet, the open-thermocouple detector protects the heater from runaway by asserting a fault bit the firmware checks every loop iteration, preventing the hot-end from continuing to heat when the probe wire fractures. Designers mount the SOIC-8 within 1 cm of the thermocouple feed-through so cold-junction compensation stays accurate, and bias the T+/T- traces with the datasheet-recommended input protection network.
推荐
HVAC Duct and Refrigeration Sensing
In HVAC duct and refrigeration systems, the MAX31855KASA+ provides digital temperature feedback for variable-air-volume boxes, chilled-water loops, and condenser coils where K-type probes are already standard. The 3.0-3.6 V supply aligns with the 3.3 V rails typical of modern building-automation controllers, and the SPI-only read protocol (one 32-bit frame per transaction) makes it easy to poll multiple ducts through a multiplexer. Open-thermocouple detection triggers a maintenance alert when the probe element fatigues, reducing unplanned service calls. The wide -270 degC to +1800 degC supported range also covers cryogenic lab and freezer applications using the same board design.
推荐
Automotive Exhaust and Engine Temperature Logging
The MAX31855KASA+ suits aftermarket automotive exhaust gas temperature (EGT) and engine coolant logging because K-type probes are standard in this segment and the 1800 degC upper range covers the worst-case turbocharger-outlet temperatures. The IC operates across -40 degC to +125 degC ambient as specified in the datasheet, tolerating under-hood thermal cycling. Designers typically place a spark-gap or TVS protection on T+/T- to survive load-dump transients and route the SPI traces away from ignition coils. The on-chip fault register lets the data-acquisition firmware flag probe burn-out without requiring an external sense resistor.
推荐
Food Service and Laboratory Equipment
Commercial ovens, sous-vide circulators, autoclaves, and laboratory temperature baths rely on the MAX31855KASA+ because the 14-bit signed output and 0.25 degC resolution meet food-code and ISO/IEC calibration requirements for process control. The SOIC-8 package handles the +125 degC ambient typical near heating elements when mounted on a thermally isolated section of the PCB, and the digital SPI output eliminates the analog noise pickup that plagues thermocouple instrumentation amplifiers in electrically noisy kitchen or lab environments. Open-thermocouple detection also satisfies HACCP documentation requirements by flagging the exact moment a probe fails during a cook cycle.
推荐
Cryogenic and High-Temperature Process Control
Because the MAX31855KASA+ supports a -270 degC to +1800 degC K-type probe range, it is one of the few single-chip converters usable across both cryogenic laboratory instrumentation (liquid nitrogen research, superconducting test rigs) and high-temperature process control (vacuum furnaces, metal heat treatment). The on-die cold-junction sensor eliminates the need for an external thermistor or RTD, simplifying the BOM and reducing drift sources. Engineers cite the part's SPI fault register as a key benefit because it lets the host controller take immediate corrective action when probes fail mid-run, rather than waiting for a watchdog timeout.
推荐
推荐产品汇总
工程参考数据： MAX31855KASA+ ——对比、设计指导和合规信息。
选型指南
与替代料对比
| 参数 | 本产品 | MAX31855JASA+ | MAX31855NASA+ | MAX31855TASA+ | MAX31855EASA+ | MAX31855KASA+T |
|---|---|---|---|---|---|---|
| Brand | Analog Devices (formerly Maxim Integrated) | Analog Devices | Analog Devices | Analog Devices | Analog Devices | Analog Devices |
| Package | 8-pin SOIC (NSOIC) | 8-pin SOIC (NSOIC) - same | 8-pin SOIC (NSOIC) - same | 8-pin SOIC (NSOIC) - same | 8-pin SOIC (NSOIC) - same | 8-pin SOIC (NSOIC) - same |
| Supported Thermocouple | K-type | J-type | N-type | T-type | E-type | K-type |
| Thermocouple Temperature Range | -270 degC to +1800 degC | -210 degC to +1200 degC | -200 degC to +1300 degC | -270 degC to +400 degC | -200 degC to +1000 degC | -270 degC to +1800 degC |
| Output Resolution | 14-bit signed (0.25 degC / LSB) | 14-bit signed (0.25 degC / LSB) | 14-bit signed (0.25 degC / LSB) | 14-bit signed (0.25 degC / LSB) | 14-bit signed (0.25 degC / LSB) | 14-bit signed (0.25 degC / LSB) |
| Output Interface | SPI (read-only, 32-bit frame) | SPI (read-only, 32-bit frame) | SPI (read-only, 32-bit frame) | SPI (read-only, 32-bit frame) | SPI (read-only, 32-bit frame) | SPI (read-only, 32-bit frame) |
| Cold-Junction Compensation | On-chip | On-chip | On-chip | On-chip | On-chip | On-chip |
| Open-Thermocouple Detection | Yes (fault register) | Yes (fault register) | Yes (fault register) | Yes (fault register) | Yes (fault register) | Yes (fault register) |
| Supply Voltage | 3.0 V to 3.6 V | 3.0 V to 3.6 V | 3.0 V to 3.6 V | 3.0 V to 3.6 V | 3.0 V to 3.6 V | 3.0 V to 3.6 V |
| Packaging Format | Tube (100-piece) | Tube (100-piece) | Tube (100-piece) | Tube (100-piece) | Tube (100-piece) | Tape & Reel (2500-piece) |
关键差异点
- On-chip cold-junction compensation with NIST polynomial linearization （对比 MAX6675ISA+)
- Higher resolution and wider temperature range （对比 MAX6675ISA+)
- On-chip open-thermocouple and short-detection （对比 MAX6675ISA+)
设计说明
Place the MAX31855KASA+ within 1-2 cm of the thermocouple screw terminals so the on-chip cold-junction sensor accurately tracks the cold-junction temperature; keep the device away from power resistors, LDO regulators, and other heat sources. Decouple VDD with a 0.1 uF ceramic capacitor placed within 5 mm of pin 4, and route the T+/T- traces as a matched-length differential pair physically separated from switching nodes or PWM signals. A small input protection network (TVS or spark gap) is recommended for automotive and industrial environments where load-dump or ESD transients can couple onto long thermocouple cable runs.
Do NOT assume the MAX31855KASA+ is code-compatible with the legacy MAX6675 - the SPI framing, clock polarity, and output data format are completely different. The MAX6675 used 12-bit unsigned output with a single falling edge on SCK; the MAX31855KASA+ uses 32-bit frames with active-low SCK, a fault register in bits[16:1], and a 14-bit signed thermocouple reading in bits[31:18]. Existing MAX6675 firmware must be rewritten. Additionally, do not power the MAX31855KASA+ from a 5 V rail - it is not 5 V tolerant and will be damaged. Use a 3.3 V regulator or level-shifters when interfacing with 5 V microcontrollers.
For SPI runs longer than ~50 mm, add 100 ohm source-series resistors on SCK, SO, and CS to dampen ringing and reduce EMI. Keep the SPI bus away from switching power converters and high-current traces; if the board has a switching regulator, route the SPI signals on the opposite layer with a continuous ground plane beneath. The MAX31855KASA+'s SCK input idles high and clocks data on the rising edge (per the datasheet timing diagram), so confirm the host MCU's SPI peripheral is configured for CPOL=1 / CPHA=1 to match the device timing.
合规信息
RoHS and lead-free compliance per DigiKey distributor listing. Not AEC-Q100 qualified - this part targets industrial and consumer applications, not automotive. REACH compliance inferred from manufacturer policy (not explicitly stated in provided data).
