Analog Devices Inc./Maxim Integrated MAX6691MUB

Overview

The MAX6691MUB from Maxim Integrated is a four-channel thermistor temperature-to-pulse-width converter that interfaces up to four NTC or PTC thermistors, delivers pulse-width modulated output via a single open-drain I/O pin, achieves ±1.0% full-scale THIGH/TLOW accuracy over -55°C to +125°C, consumes ≤10µA in sleep mode, and uses an internal 1.19–1.32V reference to reject supply noise - deployed in HVAC sensor modules for multi-zone thermal monitoring.

For engineers reviewing the MAX6691MUB datasheet, MAX6691MUB pinout, MAX6691MUB application, or MAX6691MUB equivalent, this device supports thermistor-based temperature measurement without ADC resources, enables low-power intermittent sensing in harsh environments, and requires only one microcontroller GPIO with external 10kΩ pullup for full four-sensor readout.

Technical Context

The MAX6691MUB implements a sequential voltage-divider sampling architecture: its internal VREF (1.19–1.32V) drives REXT in series with each thermistor (T1–T4), measuring VEXT across REXT to derive pulse width. Conversion is initiated by microcontroller I/O pin pull-down (≥5µs), followed by automatic 86–156ms conversion time.

Each measurement cycle produces four high/low pulse pairs on the I/O pin - THIGH proportional to VEXT (thermistor voltage), TLOW fixed at 4.0–7.5ms - with error pulses (<5% TLOW) indicating open/short thermistor faults. Power management disables VREF between conversions, reducing average thermistor current and limiting self-heating error to ~0.00036°C under typical conditions.

Key Specifications

Pinout & Package

The MAX6691MUB is housed in a 10-pin µMAX package (U10-2), 3.0mm × 3.0mm body, 0.5mm pitch, exposed pad optional, rated for -55°C to +125°C operation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar thermistor-to-digital interface applications.

Compared with MAX31865 and ADS1118, the MAX6691MUB delivers plug-and-play thermistor interfacing with zero ADC usage, deterministic pulse timing, and built-in fault detection - ideal for cost-sensitive, low-power, or MCU-constrained thermal sensing where ±1°C accuracy suffices.

Availability

The MAX6691MUB is available at Aetrix Electronics and suitable for HVAC multi-zone monitoring, medical patient temperature arrays, and home appliance thermal safety requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for MAX6691MUB 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, mixed-signal, and power-management ICs for industrial, automotive, communications, and computing applications.

The MAX6691MUB belongs to Maxim's sensor interface product line, engineered specifically to simplify thermistor-based temperature measurement in harsh, resource-constrained, or low-power embedded systems.

FAQ

What is the function of the R+ and R- pins on the MAX6691MUB?

The R+ pin outputs the MAX6691MUB's internal 1.19–1.32V reference voltage (VREF), while R- serves as the low-side connection for the external precision resistor (REXT). Together, R+ and R- form one end of the voltage divider with each thermistor (T1–T4), enabling VEXT measurement used to compute pulse width. REXT value selection directly impacts linearity and temperature range coverage.

Does the MAX6691MUB support both NTC and PTC thermistors?

Yes, the MAX6691MUB supports both NTC and PTC thermistors. Its measurement architecture relies on voltage division between REXT and thermistor resistance, making it agnostic to resistance-vs-temperature sign. However, NTC thermistors are more commonly used due to wider availability and established characterization models like Steinhart-Hart.

How does the MAX6691MUB indicate a faulty thermistor connection?

The MAX6691MUB signals thermistor faults via shortened THIGH pulses: if a thermistor is open or shorted, the corresponding THIGH duration falls below 5% of the nominal TLOW width (4.0–7.5ms). This distinct error pulse allows the host microcontroller to identify and log which channel (T1–T4) has failed without additional diagnostic circuitry.

What is the minimum microcontroller GPIO requirement to operate the MAX6691MUB?

Only one GPIO is required: an open-drain or push-pull pin configured to pull the MAX6691MUB's I/O pin low for ≥5µs to initiate conversion. A 10kΩ external pullup to VCC is mandatory. No additional pins are needed for data output, status signaling, or configuration - all communication occurs through timed pulse widths on that single I/O line.

Can the MAX6691MUB operate from a 3.3V supply in industrial environments?

Yes, the MAX6691MUB operates across 3.0V to 5.5V and is fully specified from -55°C to +125°C. At 3.3V, it delivers 1.19–1.32V VREF, ≤10µA sleep current, and maintains ±1.0% THIGH/TLOW accuracy - making it suitable for 3.3V industrial controllers, especially where low power and wide temperature range are critical.