Analog Devices Inc./Maxim Integrated MAX6855UK21D5+T

Overview

The MAX6855UK21D5+T from Maxim Integrated is a nanopower microprocessor supervisory circuit in a 5-pin SOT23 package, providing voltage monitoring, manual reset input (MR), and fixed 300ms minimum reset timeout. It asserts an active-high push-pull RESET output when VCC drops below its factory-trimmed 2.100V threshold (±2.5%), during MR assertion, or after power-up/brownout - guaranteeing valid reset down to VCC = +1.1V. It targets ultra-low-power portable systems such as glucose monitors and battery-powered medical sensors.

For engineers reviewing the MAX6855UK21D5+T datasheet, MAX6855UK21D5+T pinout, MAX6855UK21D5+T application, or MAX6855UK21D5+T equivalent, key selection criteria include its 2.100V reset threshold, 300ms reset timeout (D5 option), active-high push-pull output configuration, 170nA typical supply current at 2.5V, and guaranteed operation from –40°C to +85°C.

Technical Context

This device integrates a precision bandgap-based voltage monitor with hysteresis (0.5% of VTH), a digital reset timeout timer, and a CMOS-compatible manual reset input with 10kΩ internal pullup and 250ns MR-to-reset delay. Its reset assertion logic is synchronous to VCC transitions, with immunity to sub-40µs VCC transients when overdrive exceeds 100mV.

The MAX6855UK21D5+T belongs to the MAX6854–MAX6869 family and implements no watchdog timer or CT pin functionality - distinguishing it from MAX6864–MAX6869 (WDI) and MAX6861–MAX6863 (CT-selectable timeout). Its active-high push-pull RESET output sources up to 500µA at VCC ≥ 2.38V while maintaining VOH ≥ 0.8 × VCC.

Key Specifications

Pinout & Package

Package: 5-pin SOT23-5, lead-free (RoHS-compliant), footprint compatible with industry-standard 5-lead SOT23 layouts.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX6855UK21D5+T, the TPS3837K21DBVR demands external biasing and draws ~7× more current, while the MAX6315US21D3+ offers identical threshold but inverted reset polarity - making MAX6855UK21D5+T optimal for new designs requiring active-high, ultra-low-I_CC, and guaranteed 1.1V operation.

Availability

MAX6855UK21D5+T is available at Aetrix Electronics and suitable for glucose monitors, patient vital sign sensors, and low-power wearables requiring stable component supply with full RoHS compliance and traceable sourcing.

Supply support for MAX6855UK21D5+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 demanding industrial, medical, and communications applications.

The MAX6854–MAX6869 family delivers nanopower supervisory functions targeting battery-critical portable medical and IoT edge devices - emphasizing ultra-low ICC, guaranteed low-VCC reset validity, and minimal external component count.

FAQ

What is the exact reset threshold voltage of the MAX6855UK21D5+T?

The MAX6855UK21D5+T has a factory-trimmed reset threshold of 2.100V with ±2.5% tolerance over temperature (–40°C to +85°C), as specified in Table 2 of the datasheet under suffix "21". This value is laser-trimmed during production and does not require external calibration. The MAX6855UK21D5+T asserts RESET when VCC falls below this threshold and holds it for the full 300ms timeout after VCC rises above it.

Does the MAX6855UK21D5+T include a watchdog timer function?

No, the MAX6855UK21D5+T does not include a watchdog timer. It belongs to the MAX6854/MAX6855/MAX6856 subgroup, which provides only voltage monitoring and manual reset (MR) functionality. Watchdog capability is exclusive to MAX6864–MAX6869 variants (denoted by "S" or "L" suffixes in ordering code). The MAX6855UK21D5+T pinout lacks WDI, confirming absence of watchdog circuitry.

What is the function of Pin 4 on the MAX6855UK21D5+T?

Pin 4 on the MAX6855UK21D5+T is a second GND terminal, electrically tied to Pin 2 internally. Its inclusion improves noise immunity and thermal performance in high-reliability layouts by reducing ground impedance and distributing current paths. Unlike variants with I.C. or CT pins, the MAX6855UK21D5+T uses both Pins 2 and 4 exclusively for ground connection - no external connection or configuration is required.

Can the MAX6855UK21D5+T operate with VCC below 1.2V?

Yes, the MAX6855UK21D5+T guarantees valid RESET assertion down to VCC = +1.1V, as confirmed in the Electrical Characteristics table. While the recommended operating range starts at 1.2V, the device continues to monitor VCC and assert RESET correctly during deep brownout events between 1.1V and 1.2V. Below 1.1V, reset behavior is not characterized - hence the 1.1V lower limit is a design-critical boundary for fail-safe operation.

What does the "D5" in MAX6855UK21D5+T indicate?

The "D5" suffix in MAX6855UK21D5+T specifies the reset timeout period: D5 corresponds to a minimum 300ms reset timeout (typical 450ms, max 600ms), per Table 4 of the datasheet. This timeout begins when VCC rises above the 2.100V threshold or when MR is deasserted, and ensures the microprocessor remains held in reset long enough for power rails and clocks to stabilize before execution resumes.