Analog Devices Inc./Maxim Integrated MAX809REXR

Overview

MAX809REXR from Maxim Integrated is a precision 3-pin microprocessor supervisory circuit with push-pull active-low RESET output, designed to monitor +2.5V, +3.0V, +3.3V, and +5V power supplies in embedded systems. It asserts reset when VCC falls below 2.63V (±1.5% over temperature), maintains reset for ≥140ms after VCC recovers, draws only 17–60µA supply current, and guarantees valid reset operation down to VCC = +1V. It is used in portable equipment, automotive ECUs, and industrial controllers requiring reliable brownout detection.

For engineers reviewing the MAX809REXR datasheet, MAX809REXR pinout, MAX809REXR application, or MAX809REXR equivalent, this page delivers verified technical context, exact pin functions, real-world use cases, and validated alternative parts - all grounded in Maxim's official specifications for the SC70-3 packaged MAX809R variant.

Technical Context

The MAX809REXR integrates a precision voltage comparator with temperature-compensated reference (30ppm/°C tempco) and a monostable timer that enforces a minimum 140ms reset pulse width after VCC rises above the 2.63V threshold. Its push-pull output drives low actively without external pull-up components and remains functional across -40°C to +125°C.

It features immunity to fast VCC transients - rejecting negative glitches ≤20µs at 100mV overdrive - and ensures deterministic reset assertion even as VCC decays to 1V, where the RESET output transitions to high-impedance rather than floating unpredictably.

Key Specifications

Pinout & Package

MAX809REXR is housed in a 3-pin SC70 package (1.25mm × 2.1mm, 0.65mm pitch), rated for -40°C to +125°C operation and RoHS-compliant with lead-free option (+T suffix).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar microprocessor reset applications.

Compared with MAX809REXR, MAX809SEUR-T offers identical functionality in a larger SOT23-3 package with reduced temperature range, while TPS3808G12DBVR adds configurability at the cost of pin count, layout change, and higher BOM complexity - neither is pin-compatible, but both serve overlapping supervisory roles in distinct thermal or feature-driven contexts.

Availability

MAX809REXR is available at Aetrix Electronics and suitable for automotive engine control units, portable medical monitors, industrial PLC I/O modules, smart meter communication subsystems, and battery-powered edge sensors requiring stable component supply across extended temperature ranges.

Supply support for MAX809REXR 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, automotive, communications, and computing applications, with emphasis on reliability, low power, and small-footprint solutions.

The MAX809REXR belongs to Maxim's microprocessor supervisory product line, engineered specifically for robust power-monitoring in space-constrained, thermally demanding embedded systems where deterministic reset behavior is mission-critical.

FAQ

What is the exact reset threshold voltage of the MAX809REXR and how tightly is it specified?

The MAX809REXR has a nominal reset threshold of 2.63V, with a tolerance of ±1.5% over the full operating temperature range of -40°C to +125°C. This specification is guaranteed by design and production-tested per Maxim's datasheet, ensuring consistent brownout detection across environmental extremes without calibration. The MAX809REXR uses an internal bandgap reference with 30ppm/°C tempco to maintain accuracy.

Does the MAX809REXR require an external pull-up resistor on its RESET pin?

No, the MAX809REXR does not require an external pull-up resistor because it features a push-pull active-low RESET output. Unlike open-drain variants such as the MAX803, the MAX809REXR internally drives both high and low logic states, eliminating external components and reducing PCB area. This makes the MAX809REXR ideal for compact, high-reliability designs where layout simplicity matters.

What is the minimum VCC voltage at which the MAX809REXR guarantees correct RESET output logic state?

The MAX809REXR guarantees correct RESET output logic state down to VCC = +1V. Below that, the output enters high-impedance mode. This behavior is explicitly characterized in the datasheet and ensures predictable operation during deep brownout events. For applications requiring RESET validity down to 0V, a 100kΩ pull-down resistor on the RESET line is recommended - a design detail confirmed in Maxim's Application Information section for the MAX809REXR.

Is the MAX809REXR pin-compatible with other members of the MAX809 family, such as MAX809LEUR-T?

No, the MAX809REXR is not pin-compatible with MAX809LEUR-T due to differing packages: MAX809REXR uses SC70-3 (1.25mm × 2.1mm), while MAX809LEUR-T uses SOT23-3 (2.9mm × 1.6mm). Though both are 3-pin reset supervisors with identical pinout order (RESET-GND-VCC), their land patterns, thermal characteristics, and temperature ratings differ significantly - SC70 supports -40°C to +125°C, SOT23 only to +105°C. Layout changes are required for substitution.

What is the maximum transient duration the MAX809REXR can ignore without asserting reset?

The MAX809REXR rejects VCC transients up to 20µs in duration when the supply dips 100mV below its 2.63V reset threshold - a value confirmed in Figure 1 of the official datasheet. This transient immunity is achieved through internal filtering and comparator hysteresis, preventing false resets from switching noise, relay bounce, or ESD-induced supply disturbances. The MAX809REXR maintains this performance across its full -40°C to +125°C operating range.