Analog Devices Inc. AD8494CRMZ

Overview

AD8494CRMZ from Analog Devices is a precision J-type thermocouple amplifier with integrated cold junction compensation, delivering 5 mV/°C output, ±1°C initial accuracy at 25°C, and 0.025°C/°C ambient temperature rejection over 0°C to 50°C. It operates from single supplies (2.7 V to 36 V), draws only 180 μA quiescent current, and enables direct interface to ADCs in oven temperature monitoring systems.

For engineers reviewing the AD8494CRMZ datasheet, AD8494CRMZ pinout, AD8494CRMZ application, or AD8494CRMZ equivalent, this device serves as a drop-in signal conditioner for J-type thermocouples requiring high common-mode rejection (1°C/V), thermocouple break detection, and offset-adjustable Celsius thermometer functionality in industrial white goods and exhaust sensing.

Technical Context

The AD8494CRMZ integrates a fixed-gain (96.7) instrumentation amplifier, an on-die temperature sensor for cold junction compensation, and ESD/OVP-protected PNP-input stages. Its architecture directly converts thermocouple voltage into a linear 5 mV/°C output referenced to the REF pin, with input bias current flowing out of both IN pins enabling reliable open-circuit detection via a 1 MΩ ground resistor on −IN.

It supports measurement junction temperatures from −35°C to +95°C with ±2°C total error across its specified ambient range (0°C to 50°C), and features differential inputs rejecting common-mode noise up to 1°C/V while maintaining 25 nA max input bias current and 32 nV/√Hz voltage noise density at 1 kHz.

Key Specifications

Pinout & Package

AD8494CRMZ is housed in an RoHS-compliant 8-lead MSOP (RM-8) package with θ_JA = 135°C/W, optimized for compact PCB layouts in space-constrained thermal sensors.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AD8495ARMZ and MAX31855KASA+, AD8494CRMZ uniquely supports J-type thermocouples with analog 5 mV/°C output, wide supply range (2.7–36 V), and hardware-configurable setpoint control - making it optimal for legacy analog systems and cost-sensitive white goods.

Availability

AD8494CRMZ is available at Aetrix Electronics and suitable for oven temperature monitoring, exhaust gas sensing, Celsius thermometer modules, and setpoint controller interfaces requiring stable component supply across automotive, industrial, and appliance production programs.

Supply support for AD8494CRMZ 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

Analog Devices is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, serving industrial, communications, and automotive markets since 1965.

The AD849x family was designed specifically for thermocouple signal conditioning - integrating precision amplification, cold junction compensation, and robust input protection into a single IC to replace multi-component discrete solutions in temperature-critical systems.

FAQ

What thermocouple type is AD8494CRMZ calibrated for?

AD8494CRMZ is laser wafer trimmed for J-type (iron-constantan) thermocouples. Its fixed gain of 96.7 and internal cold junction compensation are optimized to match the Seebeck coefficient and nonlinearity of J-type wires across the full thermocouple range, ensuring accurate conversion without external linearization. Using AD8494CRMZ with K-type or other thermocouples introduces significant measurement error.

Can AD8494CRMZ measure below 0°C with a single 5 V supply?

Yes, AD8494CRMZ can measure below 0°C with a single 5 V supply by applying a positive offset voltage to the REF pin. For example, applying 2.5 V to REF shifts the output so that 0°C corresponds to 2.5 V, enabling measurements down to −35°C (output ≈ 0.75 V). This technique leverages the device's 1 V/V REF-to-OUT gain and rail-to-rail output swing capability.

How does AD8494CRMZ detect an open thermocouple connection?

AD8494CRMZ detects an open thermocouple by exploiting its PNP-input architecture: input bias current flows *out* of both −IN and +IN pins. When the thermocouple breaks, −IN floats and is pulled high by its 1 MΩ ground resistor, driving the output to the positive rail. This rail-high condition provides immediate hardware fault indication without requiring external comparators or firmware polling.

What is the maximum thermocouple measurement junction temperature supported by AD8494CRMZ?

AD8494CRMZ supports measurement junction temperatures from −35°C to +95°C with ±2°C total error when used within its specified ambient temperature range (0°C to 50°C). At higher junction temperatures, output voltage may exceed the supply rails unless the supply voltage is increased above 5 V or the REF pin is biased negatively - per the datasheet's guidance for extended-range operation.

Does AD8494CRMZ require external passive components for basic operation?

AD8494CRMZ operates as a complete signal conditioner with no external gain or offset components required. However, Analog Devices recommends a low-pass RC filter (R ≤ 50 kΩ, C ≥ 1 nF) at the inputs to suppress RF interference picked up by thermocouple leads, and a 1 MΩ resistor from −IN to ground for open-circuit detection - both are simple, low-cost additions that significantly improve real-world reliability.