What the MAX921ESA+T is and where it fits
The MAX921ESA+T from Maxim Integrated is a single comparator with an integrated voltage reference, combining threshold detection and a precision 1.182V reference in one 8-SOIC package. It is designed for battery-powered threshold monitoring, undervoltage/overvoltage detection, and window comparators where every microamp counts. The built-in 50mV hysteresis eliminates the need for external positive feedback resistors, saving board space and BOM cost. The 5µA max quiescent current makes it a strong fit for always-on sensor monitors, portable instrumentation, and industrial control loops that must stay alive on a coin cell or energy-harvesting supply. The 2.5V to 11V single-supply range (or ±1.25V to ±5.5V dual) covers common 3.3V and 5V rails with headroom for 12V industrial buses.
Industrial temperature range and environment
Rated for -40°C to 85°C operation, the MAX921ESA+T suits outdoor telecom cabinets, factory-floor sensors, engine-bay monitors (non-AEC), and HVAC controllers. The 80dB CMRR and PSRR keep threshold accuracy stable across supply droops and common-mode shifts common in noisy industrial backplanes.
Output drive and response time
The CMOS/TTL output can sink or source 50mA typical, enough to drive a small relay coil, an LED indicator, or the enable pin of a downstream regulator directly. The 12µs max propagation delay is adequate for DC threshold and low-frequency monitoring; for high-speed PWM or zero-crossing detection, a faster comparator family would be needed.
Sourcing and lifecycle
The MAX921ESA+T is listed as Active and ROHS3 compliant. There is no NRND or LTB flag, so it remains a safe choice for new designs and production replenishment.