Analog Devices Inc./Maxim Integrated MAX31851RATB+T

Overview

MAX31851RATB+T from Maxim Integrated is a cold-junction compensated, 1-Wire thermocouple-to-digital converter optimized for R-type thermocouples. It delivers 14-bit resolution (0.25°C), supports thermocouple temperature range from –50°C to +1768°C, achieves ±7°C total error over full operating range (–40°C to +125°C), and integrates fault detection for open/shorted thermocouple leads. It is used in high-temperature industrial furnace monitoring where single-wire digital interface and parasitic power simplify sensor node deployment.

For engineers reviewing the MAX31851RATB+T datasheet, MAX31851RATB+T pinout, MAX31851RATB+T application, or MAX31851RATB+T equivalent, key selection considerations include R-type thermocouple support, 1-Wire read-only interface timing compliance, cold-junction compensation accuracy at elevated ambient temperatures, and AD0–AD3 address pin mapping for multi-node bus configuration.

Technical Context

The MAX31851RATB+T implements a dedicated analog front-end with programmable gain and offset correction tailored to R-type thermocouple sensitivity (10.506 µV/°C), coupled with a 14-bit sigma-delta ADC and integrated die temperature sensor for cold-junction compensation. Its internal switch matrix isolates thermocouple inputs during cold-junction measurement and fault detection phases.

It operates in either local VDD-powered mode or parasite-power mode via DQ, requiring external strong pullup during conversion (tCONV = 72–100 ms). The device uses a fixed 64-bit ROM with family code 0x3B and reports location address bits AD3–AD0 in Scratchpad Byte 4, enabling deterministic node identification on shared 1-Wire buses.

Key Specifications

Pinout & Package

TDFN-EP (3mm × 4mm, 10-pin, exposed pad); RoHS-compliant; moisture sensitivity level MSL-1.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar thermocouple digitizer applications.

Compared with MAX31851SATB+T, the MAX31851RATB+T offers higher full-scale range (+1768°C vs. +1768°C) but tighter R-type gain matching, while AD8495ARZ shifts responsibility for digitization and bus management to the host system-increasing design effort but offering greater signal-chain flexibility.

Availability

MAX31851RATB+T is available at Aetrix Electronics and suitable for industrial furnace monitoring, HVAC duct sensing, medical autoclave validation, and power generation boiler monitoring requiring stable component supply and long-term calibration integrity.

Supply support for MAX31851RATB+T includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Maxim Integrated (now part of Analog Devices) designs precision analog and mixed-signal ICs for industrial, medical, and communications systems, with emphasis on signal integrity and low-power operation.

The MAX31850/MAX31851 product line targets distributed temperature sensing applications requiring direct thermocouple digitization, cold-junction compensation, and minimal wiring-enabling robust, scalable sensor networks in harsh environments.

FAQ

What thermocouple types does the MAX31851RATB+T support?

The MAX31851RATB+T is factory-calibrated exclusively for R-type thermocouples, with nominal sensitivity of 10.506 µV/°C and guaranteed performance from –50°C to +1768°C. It does not support K-, J-, N-, T-, S-, or E-type thermocouples-those require corresponding MAX31850/51 variants (e.g., MAX31851SATB+T for S-type). Using an R-type thermocouple with the MAX31851RATB+T ensures optimal accuracy and avoids gain/offset errors inherent in cross-type operation.

How does the MAX31851RATB+T handle cold-junction compensation?

The MAX31851RATB+T integrates a precision die temperature sensor that measures its own junction temperature, then applies algorithmic correction to the R-type thermocouple voltage using the known 10.506 µV/°C slope. This yields cold-junction-compensated temperature values stored in Scratchpad Bytes 0–1, with ±2°C error over –40°C to +100°C ambient. No external reference sensor or compensation circuitry is needed-the MAX31851RATB+T performs full compensation autonomously.

Can the MAX31851RATB+T operate without a local power supply?

Yes, the MAX31851RATB+T supports parasite-power mode via the DQ pin, eliminating the need for a local VDD supply. In this mode, VDD must be grounded, and a strong external pullup (e.g., MOSFET-switched rail) is required during temperature conversions (72–100 ms) to deliver up to 1.5 mA. Parasite power is validated up to +100°C ambient; for sustained operation above that, local VDD powering is recommended to maintain communication reliability.

What fault conditions does the MAX31851RATB+T detect?

The MAX31851RATB+T detects three thermocouple faults: open circuit (bit 0 high in Scratchpad Byte 2), short to GND (bit 1 high), and short to VDD (bit 2 high). These flags appear alongside internal cold-junction temperature data in Bytes 2–3. A fault condition also sets bit 0 of the compensated thermocouple temperature (Byte 0, MSb) to indicate invalid reading-enabling immediate host-level error handling without post-processing.

How are the AD0–AD3 pins used in the MAX31851RATB+T?

The AD0–AD3 pins (Pins 6–9) are hardwired address inputs that define a 4-bit location code for the MAX31851RATB+T on a shared 1-Wire bus. Their logic states (0 = GND, 1 = DQ or pullup) are latched at power-up and reported in Bits [3:0] of Scratchpad Byte 4. This allows up to 16 uniquely addressable MAX31851RATB+T units per bus segment, simplifying zone-based sensor mapping without requiring individual ROM searches.