Analog Devices Inc./Maxim Integrated MAX6855UK21D3+T

Overview

The MAX6855UK21D3+T from Maxim Integrated is a nanopower microprocessor supervisory circuit in a 5-pin SOT23 package, featuring ultra-low 170nA typical supply current, factory-trimmed 2.100V reset threshold (suffix '21'), and 150ms minimum reset timeout (suffix 'D3'). It provides active-high push-pull RESET output, manual reset input (MR), and operates across -40°C to +85°C - designed for reliable power-on reset and brownout protection in battery-critical portable medical and consumer devices.

For engineers reviewing the MAX6855UK21D3+T datasheet, MAX6855UK21D3+T pinout, MAX6855UK21D3+T application, or MAX6855UK21D3+T equivalent, key selection criteria include its guaranteed RESET validity down to VCC = +1.1V, immunity to short VCC transients (<40µs at 100mV overdrive), pin-selectable reset delay capability (not applicable to this variant), and compatibility with low-voltage µP interfaces requiring active-high assertion logic.

Technical Context

This device implements a precision voltage monitor with hysteresis (±2.5% VTH), a fixed 150ms reset timeout timer, and a CMOS-compatible manual reset input with 10kΩ internal pullup and 250ns MR-to-RESET delay. It asserts RESET high when VCC falls below 2.100V or MR is pulled low, holding the signal for ≥150ms after VCC recovers and MR deasserts.

No watchdog timer or CT pin functionality is present - MAX6855UK21D3+T belongs to the MR-only, active-high push-pull RESET subgroup (per Selector Guide). Its open-drain alternatives are excluded; this variant drives RESET directly to VCC or GND without external pullup.

Key Specifications

Pinout & Package

Package: 5-pin SOT23-5 (lead-free, +T suffix), 2.9mm × 1.6mm footprint, 1.1mm height - compatible with high-density portable PCB layouts and reflow assembly.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TPS3837K21DBVR and MAX6315US21D3+, the MAX6855UK21D3+T delivers the lowest quiescent current (170nA vs. ≥1.2µA), enabling longest battery life in portable medical and consumer devices - while maintaining identical 2.1V/150ms/active-high functional behavior and SOT23-5 pin compatibility.

Availability

MAX6855UK21D3+T is available at Aetrix Electronics and suitable for portable glucose monitors, wireless patient loggers, and low-power smart pagers requiring stable component supply with long-term lifecycle assurance and lead-free compliance.

Supply support for MAX6855UK21D3+T 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 power management, sensing, and interface applications - with emphasis on ultra-low-power, high-reliability solutions for medical and portable electronics.

The MAX685x family delivers nanopower supervisory functions targeting battery-operated systems where reset accuracy, minimal current draw, and guaranteed low-VCC operation are critical - especially in FDA-regulated diagnostic equipment.

FAQ

What is the exact reset threshold voltage of the MAX6855UK21D3+T?

The MAX6855UK21D3+T has a factory-trimmed reset threshold voltage of 2.100V, with ±2.5% tolerance over temperature (-40°C to +85°C). This value is confirmed by the '21' suffix in the part number per Maxim's Threshold Suffix Guide (Table 2), and is validated in the Electrical Characteristics table under VTH parameter.

Does the MAX6855UK21D3+T include a watchdog timer function?

No, the MAX6855UK21D3+T does not include a watchdog timer. Per the Selector Guide and Pin Description, only MAX6864–MAX6869 variants feature WDI input; MAX6855 belongs to the MR-only subgroup and lacks both WDI and CT pins. Its functionality is limited to voltage monitoring and manual reset.

What is the reset timeout period for the MAX6855UK21D3+T?

The MAX6855UK21D3+T has a minimum reset timeout period of 150ms, indicated by the 'D3' suffix per Table 4 (Reset Timeout Periods). Typical and maximum values are 225ms and 300ms respectively, ensuring sufficient time for microprocessor initialization before release from reset.

Is the RESET output of the MAX6855UK21D3+T push-pull or open-drain?

The MAX6855UK21D3+T features an active-high push-pull RESET output, as confirmed by the Selector Guide (MAX6855 row shows √ under "Push-Pull ACTIVE HIGH") and Pin Description (Pin 1 labeled RESET with active-high behavior). It drives high to VCC when asserted and low to GND when deasserted - no external pullup required.

Can the MAX6855UK21D3+T operate reliably below 1.8V supply voltage?

Yes, the MAX6855UK21D3+T operates down to VCC = +1.2V (minimum specified) and guarantees valid RESET output down to VCC = +1.1V. Its 170nA supply current remains stable across the full 1.2V–5.5V range, making it suitable for 1.5V alkaline or 1.8V LiFePO₄-based systems.