Analog Devices Inc./Maxim Integrated MAX921MJA

Overview

MAX921MJA from Maxim Integrated is a single-channel, ultra-low-power voltage comparator with integrated 1.182V ±1% bandgap reference, programmable hysteresis via HYST pin, and TTL/CMOS-compatible output capable of sourcing up to 40mA. It operates from +2.5V to +11V single supply (or ±1.25V to ±5.5V dual supply), supports rail-to-rail input common-mode range down to V− and within 1.3V of V+, and is qualified for −55°C to +125°C military temperature operation in 8-pin CERDIP package. It is used in battery-powered threshold detection where low quiescent current and stable reference are critical.

For engineers reviewing the MAX921MJA datasheet, MAX921MJA pinout, MAX921MJA application, or MAX921MJA equivalent, key selection considerations include its guaranteed 4µA max supply current over full military temperature range, internal reference accuracy, hysteresis configurability without external feedback, and output drive capability enabling direct LED or logic interface without buffering.

Technical Context

The MAX921MJA implements a micropower comparator core paired with a precision bandgap reference referenced to V−, not GND. Its unique output stage eliminates crowbar current during transitions, minimizing supply-line parasitic feedback and improving stability in noisy or poorly decoupled layouts.

Input common-mode range extends from V− to (V+ − 1.3V); inputs tolerate ±0.3V beyond supply rails without damage. Hysteresis is implemented via the HYST pin, accepting 0–50mV below REF to set symmetric threshold bands up to 100mV wide - a feature exclusive to MAX921 and MAX923 variants.

Key Specifications

Pinout & Package

MAX921MJA is housed in an 8-pin CERDIP (Ceramic Dual In-line Package) with hermetic sealing suitable for high-reliability military and aerospace applications. Pin 1 is OUT, pin 2 is V−, pin 3 is IN+, pin 4 is IN−, pin 5 is HYST, pin 6 is REF, pin 7 is V+, pin 8 is GND.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX921ESA and LM393AMX/NOPB, MAX921MJA delivers guaranteed sub-4µA operation across −55°C to +125°C, eliminates external reference and hysteresis resistors, and provides 40mA output drive - making it uniquely suited for high-reliability, long-life, component-count-sensitive designs.

Availability

MAX921MJA is available at Aetrix Electronics and suitable for battery-powered systems, threshold detectors, window comparators, and oscillator circuits requiring stable component supply under extreme environmental conditions.

Supply support for MAX921MJA 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 performance, reliability, and power-efficiency requirements.

The MAX921–MAX924 family was developed specifically for ultra-low-power, single/dual-supply comparator applications requiring integrated reference, programmable hysteresis, and robust output drive in harsh environments.

FAQ

What is the maximum supply voltage rating for MAX921MJA?

The MAX921MJA has an absolute maximum supply voltage rating of +12V between V+ and V−, and operation is specified from +2.5V to +11V single supply (or ±1.25V to ±5.5V dual supply). Exceeding +12V may cause permanent damage, and operation above +11V is outside guaranteed specifications. The device's CERDIP package supports reliable operation at these voltages across its full −55°C to +125°C temperature range.

Does MAX921MJA require external bypass capacitors?

Power-supply bypass capacitors are not required for MAX921MJA if the supply impedance is low; however, a 100nF ceramic capacitor is recommended when supply leads are long or source impedance is high. Critically, the REF pin must never be bypassed - doing so degrades reference stability and increases noise. The device's crowbar-free output stage further reduces sensitivity to supply noise, minimizing need for aggressive decoupling.

How is hysteresis configured on MAX921MJA?

Hysteresis on MAX921MJA is configured using the HYST pin: connect R1 between REF and HYST, and R2 between HYST and V−. The hysteresis band equals approximately twice (REF − V_HYST), with V_HYST adjustable from REF down to (REF − 50mV), yielding up to 100mV total hysteresis. This method requires no external feedback and maintains ultra-low quiescent current - a capability exclusive to MAX921 and MAX923 variants.

What is the output voltage swing of MAX921MJA?

MAX921MJA's output swings from V+ to GND in single-supply configuration (V− = GND), delivering TTL/CMOS-compatible logic levels with +5V supply. Output high voltage is typically V+ − 0.4V at 10mA load; output low voltage is typically GND + 0.4V. The output continuously sources up to 40mA and sinks up to 50mA, enabling direct drive of LEDs, small relays, or logic inputs without external buffers.

Is the internal reference of MAX921MJA referenced to GND or V−?

The internal 1.182V reference of MAX921MJA is referenced to V−, not GND. This means REF = V− + 1.182V, which is essential for correct operation in dual-supply configurations (e.g., ±5V) and affects resistor-divider design for threshold setting. When V− = GND (single supply), REF is effectively 1.182V above ground. Deviation from this reference point invalidates all reference-based calculations.