Analog Devices Inc./Maxim Integrated MAX31851RATB+

Overview

MAX31851RATB+ 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 - used in high-temperature industrial furnace monitoring.

For engineers reviewing the MAX31851RATB+ datasheet, MAX31851RATB+ pinout, MAX31851RATB+ application, or MAX31851RATB+ equivalent, key selection considerations include R-type thermocouple support, parasitic power capability, 1-Wire multdrop architecture, cold-junction compensation accuracy, and TDFN-EP (3mm × 4mm) package compatibility with space-constrained sensor nodes.

Technical Context

The MAX31851RATB+ implements a dedicated analog front-end with programmable gain and offset correction tailored to R-type thermocouple sensitivity (10.506 µV/°C), coupled with an internal 14-bit ADC and die-temperature sensing for cold-junction compensation. Its conversion sequence executes three synchronized operations: thermocouple voltage digitization, internal cold-junction temperature measurement, and fault detection (open/short-to-VDD/GND).

Communication follows the 1-Wire protocol with strict timing requirements: reset pulse low time ≥480 µs, time slot 60–120 µs, and presence detect window 15–240 µs. Power delivery supports dual modes - local VDD supply (3.0–3.7 V) or parasite power via DQ with strong pullup required during 72–100 ms conversion cycles.

Key Specifications

Pinout & Package

TDFN-EP (3mm × 4mm, 10-pin) with exposed pad (EP); EP has no internal connection and may be grounded or left floating for thermal/mechanical stability.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar thermocouple-to-digital conversion applications.

Compared with MAX31856ASA+, MAX31851RATB+ trades multi-type flexibility and resolution for 1-Wire simplicity and lower system-level component count; compared with AD8495ARZ, it eliminates external ADC dependency and provides built-in fault reporting - reducing validation effort in safety-critical thermal monitoring.

Availability

MAX31851RATB+ is available at Aetrix Electronics and suitable for industrial furnace monitoring, HVAC high-temperature duct sensing, and medical sterilization autoclave control requiring stable component supply and long-lifecycle assurance.

Supply support for MAX31851RATB+ 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 demanding industrial, medical, and communications applications.

The MAX31851RATB+ belongs to Maxim's thermocouple interface product line, engineered specifically for high-accuracy, low-power, and easy-deployment digital temperature sensing in extreme-temperature environments.

FAQ

What thermocouple types does the MAX31851RATB+ support?

The MAX31851RATB+ is factory trimmed 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 MAX31850 variants or the multi-type MAX31856. Using an R-type thermocouple with MAX31851RATB+ ensures optimal accuracy without software linearization.

Can the MAX31851RATB+ operate without an external power supply?

Yes, the MAX31851RATB+ supports parasite power mode: VDD is connected to GND, and operating power is drawn from the 1-Wire bus through the DQ pin during high states. However, a strong pullup (e.g., MOSFET-switched rail) must be activated within 10 µs after issuing the Convert T command and held for the full 72–100 ms conversion period. Parasite power is not recommended above +100°C due to leakage current concerns.

How does the MAX31851RATB+ handle cold-junction compensation?

The MAX31851RATB+ integrates a precision die-temperature sensor and applies real-time correction to the R-type thermocouple voltage using its known 10.506 µV/°C sensitivity. The internal cold-junction temperature is measured simultaneously with thermocouple conversion and stored in scratchpad bytes 2–3. Total cold-junction error is ±2°C from –40°C to +100°C ambient, enabling accurate "hot junction" calculation without external sensors.

What fault conditions does the MAX31851RATB+ detect and report?

The MAX31851RATB+ 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 the internal temperature value and are latched until cleared by a new conversion. No external components or firmware logic are needed - fault status is available immediately after reading scratchpad byte 2.

Is the MAX31851RATB+ pin-compatible with other MAX3185x devices?

Yes, the MAX31851RATB+ shares identical TDFN-EP (3mm × 4mm, 10-pin) packaging and pinout with MAX31850 variants (e.g., MAX31850KATB+) and MAX31851S. Pin functions - including GND, T–, T+, VDD, DQ, AD0–AD3, and DNC - are fully consistent across the family. This allows drop-in replacement when upgrading from K/J/N/T/E to R/S-type thermocouple support, provided firmware addresses the correct device ROM family code (3Bh).