Analog Devices Inc./Maxim Integrated MAX6855UK21D4+T

Overview

The MAX6855UK21D4+T from Maxim Integrated is a nanopower microprocessor supervisory circuit in a 5-pin SOT23 package, featuring ultra-low 170nA typical supply current, a factory-trimmed 2.100V reset threshold (suffix "21"), and a 1200ms minimum reset timeout (suffix "D4"). It provides active-high push-pull RESET output, manual reset input (MR), and voltage monitoring for brownout detection - used to ensure reliable power-up sequencing in battery-powered medical and portable electronics.

For engineers reviewing the MAX6855UK21D4+T datasheet, MAX6855UK21D4+T pinout, MAX6855UK21D4+T application, or MAX6855UK21D4+T equivalent, key selection criteria include its guaranteed reset validity down to VCC = +1.1V, immunity to short VCC transients (<40µs at 100mV overdrive), push-pull active-high output configuration, and compatibility with low-voltage µP systems operating from 1.2V to 5.5V.

Technical Context

This device integrates three core functions: precision voltage monitoring with ±2.5% threshold accuracy, a manual reset input with 250ns MR-to-reset delay and internal 10kΩ pullup, and a fixed 1200ms reset timeout timer that holds RESET asserted after VCC recovery or MR release. Its BiCMOS process enables stable operation across –40°C to +85°C with no external components required.

The MAX6855UK21D4+T lacks watchdog timer (WDI) and CT (timeout select) pins - confirmed by its absence in the Selector Guide and Pin Description tables for MAX6855. Its active-high push-pull RESET output sources up to 500µA at VOH ≥ 0.8×VCC (VCC ≥ 2.38V) and sinks <0.3V at VOL when asserted, enabling direct interface with µP reset inputs without external pullups.

Key Specifications

Pinout & Package

MAX6855UK21D4+T is housed in a lead-free 5-pin SOT23-5 package (JEDEC MO-178AA), with 1.3mm × 2.9mm body size and 0.95mm pitch. Pin 1 is marked with a dot; orientation follows standard SOT23 top-view labeling.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TPS3837K21QDBVR and ADM6805-21ARTZ-RL, the MAX6855UK21D4+T delivers superior energy efficiency and deeper brownout coverage - essential for medical wearables and long-life IoT nodes where every nanoamp impacts field reliability and service interval.

Availability

MAX6855UK21D4+T is available at Aetrix Electronics and suitable for glucose monitors, patient vital sign recorders, handheld diagnostics, low-power IoT trackers, and portable medical instrumentation requiring stable component supply across extended product lifecycles.

Supply support for MAX6855UK21D4+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) is a semiconductor company specializing in high-performance analog, mixed-signal, and power management ICs for industrial, medical, and communications applications.

The MAX6854–MAX6869 family was designed specifically for ultra-low-power microprocessor supervision in battery-constrained medical and portable equipment - emphasizing nanopower operation, precise voltage thresholds, and robust reset timing without external components.

FAQ

What is the exact reset threshold voltage of the MAX6855UK21D4+T?

The MAX6855UK21D4+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 defined by the "21" suffix in the part number and is verified per Table 2 (Threshold Suffix Guide) in the datasheet. The MAX6855UK21D4+T asserts RESET when VCC falls below this threshold and holds it for 1200ms after VCC recovers.

Does the MAX6855UK21D4+T include a watchdog timer function?

No, the MAX6855UK21D4+T does not include a watchdog timer. Per the Selector Guide and Pin Configuration diagrams, only MAX6864–MAX6869 variants feature WDI input; the MAX6855UK21D4+T is a manual-reset-only supervisory circuit with MR input and no watchdog-related pins or timing circuitry.

What is the function of Pin 4 on the MAX6855UK21D4+T?

Pin 4 on the MAX6855UK21D4+T is a second GND terminal, electrically connected to Pin 2 internally. Its inclusion improves thermal dissipation and reduces ground impedance in high-noise environments. Both GND pins must be soldered to the PCB ground plane - splitting return paths is not recommended.

Can the MAX6855UK21D4+T operate reliably at VCC = 1.2V?

Yes, the MAX6855UK21D4+T is fully specified to operate from VCC = 1.2V to 5.5V. Its reset output remains valid down to VCC = 1.1V, and supply current is characterized at 1.2V (190nA typ). This makes the MAX6855UK21D4+T suitable for single-cell alkaline or NiMH systems where voltage drops near end-of-life.

Is the MAX6855UK21D4+T pin-compatible with other devices in the MAX6854–MAX6869 family?

The MAX6855UK21D4+T shares the same 5-pin SOT23-5 package and pinout as MAX6854, MAX6856, MAX6861–MAX6863, and MAX6864–MAX6869 variants - but functional compatibility depends on configuration. While Pin 1 (RESET), Pin 2/4 (GND), Pin 3 (MR), and Pin 5 (VCC) are identical, the MAX6855UK21D4+T's active-high push-pull output differs from open-drain or active-low variants, requiring verification of µP reset input polarity.