Analog Devices Inc./Maxim Integrated MAX6821ZUK

Overview

MAX6821ZUK from Maxim Integrated is a low-voltage microprocessor supervisory IC in SOT23-5 package, providing voltage monitoring (2.32V threshold), 140ms minimum reset timeout, 1.6s watchdog timer, manual reset input, and push-pull active-low RESET output. It ensures reliable µP initialization during power-up, brownout, and software fault conditions in battery-powered embedded systems.

For engineers reviewing the MAX6821ZUK datasheet, MAX6821ZUK pinout, MAX6821ZUK application, or MAX6821ZUK equivalent, this device serves as a precision reset supervisor for +2.1V to +2.75V supply rails with guaranteed reset validity down to VCC = +1.0V, immunity to short negative VCC transients, and no external components required.

Technical Context

The MAX6821ZUK integrates a precision bandgap-based voltage monitor with 60ppm/°C temperature coefficient and 2×VTH hysteresis, a monostable watchdog timer cleared by WDI edge transitions, and a debounced manual reset input with internal 50kΩ pullup. Its push-pull RESET output drives low with VOL ≤ 0.4V at ISINK = 3.2mA (VCC ≥ 4.75V) and releases high with VOH ≥ 0.8×VCC (ISOURCE = 800µA).

It operates across -40°C to +125°C with supply current as low as 5µA at VCC = +1.8V (typical), supports VCC monitoring from +2.1V to +2.75V (Z-suffix threshold), and asserts reset within 20µs of VCC falling below 2.32V. The watchdog timeout is specified at 1.6s (min 0.80s, max 2.60s over temperature).

Key Specifications

Pinout & Package

MAX6821ZUK is housed in a 5-pin SOT23-5 package (JEDEC MO-178AA), 2.9mm × 1.6mm × 1.1mm, surface-mount, lead-free compatible.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX6821ZUK, MAX6326UR23 reduces footprint but removes critical watchdog and manual reset capabilities, while TPS3808G125DBVR offers lower ICC but requires layout changes for pullup and lacks field-service reset - making MAX6821ZUK the only option integrating all three functions in SOT23-5.

Availability

MAX6821ZUK is available at Aetrix Electronics and suitable for portable medical devices, industrial sensor nodes, automotive body control modules, smart energy meters, and battery-powered instrumentation requiring stable component supply across extended temperature ranges.

Supply support for MAX6821ZUK 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 demanding industrial, automotive, and computing applications.

The MAX6821–MAX6825 family was engineered specifically for low-voltage microprocessor supervision in space-constrained, battery-operated systems requiring integrated voltage monitoring, watchdog, and manual reset in a single SOT23-5 package.

FAQ

What is the exact reset threshold voltage for MAX6821ZUK?

The MAX6821ZUK has a factory-programmed reset threshold of 2.32V (Z-suffix), with tolerance of ±12mV over -40°C to +125°C. This value is guaranteed across its specified operating range of VCC = +2.1V to +2.75V, and the device asserts RESET when VCC falls below this threshold and holds it for ≥140ms after VCC rises above it. The MAX6821ZUK datasheet specifies typical hysteresis of 2×VTH (≈4.64mV) to prevent chatter near the trip point.

Does MAX6821ZUK include a watchdog timer, and what is its timeout period?

Yes, the MAX6821ZUK includes a watchdog timer with a nominal timeout period of 1.6 seconds. The actual timeout ranges from 0.80s (min) to 2.60s (max) over -40°C to +125°C. The timer is cleared by any rising or falling edge on the WDI pin, and it is disabled when WDI is left unconnected or driven high-impedance. The MAX6821ZUK watchdog is designed to detect µP code execution errors without requiring firmware modifications.

What type of RESET output does MAX6821ZUK provide, and how is it configured?

The MAX6821ZUK provides an active-low push-pull RESET output (pin 1). Unlike open-drain variants, this configuration actively drives both high and low states, eliminating the need for an external pullup resistor. When asserted, RESET sinks up to 3.2mA with VOL ≤ 0.4V (VCC ≥ 4.75V); when deasserted, it sources up to 800µA with VOH ≥ 0.8×VCC. This makes MAX6821ZUK compatible with µPs having bidirectional reset I/O or strict drive-strength requirements.

Can MAX6821ZUK operate reliably at very low supply voltages?

Yes, the MAX6821ZUK guarantees correct RESET assertion and timing functionality down to VCC = +1.0V, well below its 2.32V threshold. This ensures deterministic behavior during deep brownout conditions common in battery-depleted systems. Its internal circuitry remains functional and stable across the full VCC range of +2.1V to +2.75V (Z-version), with supply current as low as 5µA (typical) at +1.8V, making MAX6821ZUK suitable for ultra-low-power applications.

How is the manual reset input (MR) implemented on MAX6821ZUK?

The MAX6821ZUK features an active-low manual reset input (MR, pin 3) with an internal 50kΩ pullup resistor to VCC. Pulling MR low forces RESET assertion for the full 140ms timeout period, even if VCC is stable. MR accepts CMOS-compatible logic levels (VIL ≤ 0.3×VCC, VIH ≥ 0.7×VCC) and rejects glitches <100ns. When unused, MR may be left floating or tied to VCC; no external components are needed to implement field-service or test-mode reset functionality with MAX6821ZUK.