Analog Devices Inc./Maxim Integrated MAX6821RUK

Overview

MAX6821RUK from Maxim Integrated is a low-voltage microprocessor supervisory IC in 5-pin SOT23 package, combining voltage monitoring (2.63V threshold), 140ms minimum reset timeout, 1.6s watchdog timer, manual reset input, and push-pull active-low RESET output. It ensures reliable µP startup and brownout recovery in space-constrained embedded systems.

For engineers reviewing the MAX6821RUK datasheet, MAX6821RUK pinout, MAX6821RUK application, or MAX6821RUK equivalent, this device serves as a precision reset supervisor for +2.5V/+3.3V systems requiring guaranteed reset validity down to VCC = +1.0V, immunity to short negative VCC transients, and no external components.

Technical Context

The MAX6821RUK implements a precision bandgap-based voltage monitor with 60ppm/°C temperature coefficient and 2×VTH hysteresis, ensuring stable reset assertion during VCC ramp-up/down. Its internal reset generator holds RESET low for ≥140ms after VCC exceeds 2.63V, independent of supply voltage decay rate.

A dedicated watchdog transition detector monitors WDI edges with 50ns pulse-width sensitivity and clears the 1.6s timeout on any rising or falling edge; the timer remains frozen while RESET is asserted. MR features an internal 50kΩ pullup and 100ns glitch rejection, enabling direct switch-to-GND connection without external debounce.

Key Specifications

Pinout & Package

MAX6821RUK uses a 5-pin SOT23-5 package (1.6mm × 2.9mm × 1.1mm) with standard JEDEC MO-178AC outline and gull-wing leads.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX6821RUK, MAX6326UT26D+ reduces cost and size but removes critical safety layers (watchdog, MR), while TPS3808G18DBVR extends voltage range at the expense of manual reset capability and push-pull drive strength-making MAX6821RUK optimal for integrated, self-contained supervision in compact industrial and automotive nodes.

Availability

MAX6821RUK is available at Aetrix Electronics and suitable for industrial PLC controllers, automotive body control modules, and portable medical monitors requiring stable component supply, long-term lifecycle support, and AEC-Q200-aligned reliability.

Supply support for MAX6821RUK 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, and computing applications, with emphasis on power management, sensing, and interface solutions.

The MAX6821–MAX6825 family targets space-constrained embedded systems needing integrated voltage monitoring, watchdog, and manual reset in a single 5-pin SOT23-replacing discrete reset generators and simplifying compliance with IEC 61508 functional safety prerequisites.

FAQ

What is the exact reset threshold voltage for MAX6821RUK?

The MAX6821RUK has a factory-trimmed reset threshold of 2.63V ±10mV (minimum 2.53V, maximum 2.72V) over the full -40°C to +125°C temperature range. This value is specified under VCC falling conditions and includes 2×VTH hysteresis to prevent chatter near the threshold. The 'R' suffix in MAX6821RUK explicitly denotes the 2.63V option per Maxim's Threshold Suffix Guide.

Does MAX6821RUK support operation below 1.8V supply voltage?

Yes, MAX6821RUK guarantees valid reset assertion down to VCC = +1.0V, and its operational voltage range is specified from +1.2V to +5.5V. At VCC = +1.2V, the device maintains full functionality including 2.63V threshold monitoring, 140ms reset timeout, and MR/WDI input responsiveness-enabling use in ultra-low-power wake-up circuits and energy-harvesting systems.

How does the watchdog timer in MAX6821RUK interact with the manual reset function?

In MAX6821RUK, asserting MR low immediately triggers a reset and clears the watchdog timer. The reset remains active for the full 140ms timeout period regardless of MR release timing. While RESET is asserted, the watchdog timer stays frozen and does not count; it only resumes counting after RESET returns to its inactive state. This ensures deterministic behavior during maintenance resets.

Can MAX6821RUK's RESET output drive a microcontroller with a bidirectional reset pin?

No-MAX6821RUK features a push-pull active-low RESET output, which cannot safely interface with bidirectional µP reset pins (e.g., Motorola 68HC11) that may drive the line high. For such applications, use MAX6822RUK (open-drain RESET) instead. MAX6821RUK's push-pull design is optimized for standard active-low reset inputs requiring direct drive without external pullups.

What is the maximum allowable leakage current on the WDI pin of MAX6821RUK when unused?

When WDI is left unconnected or three-stated, MAX6821RUK specifies a maximum leakage current of 10µA and maximum load capacitance of 200pF to ensure reliable watchdog disablement. The internal driver cycles low-high-low every 1.4s to service the timer, so external leakage exceeding 10µA could prevent proper disablement and cause unintended resets.