Analog Devices Inc./Maxim Integrated MAX6855UK21D1+T

Overview

The MAX6855UK21D1+T from Maxim Integrated is a nanopower microprocessor supervisory circuit in a 5-pin SOT23 package, providing voltage monitoring, manual reset input (MR), and active-low push-pull reset output. It asserts reset when VCC drops below 2.100V (factory-trimmed threshold), MR is pulled low, or during power-up/brownout - with guaranteed reset validity down to VCC = +1.1V and ultra-low 170nA typical supply current. It serves as a critical power-on reset and fault recovery element in battery-powered medical and portable electronics.

For engineers reviewing the MAX6855UK21D1+T datasheet, MAX6855UK21D1+T pinout, MAX6855UK21D1+T application, or MAX6855UK21D1+T equivalent, key selection criteria include its 2.100V reset threshold, 10ms minimum reset timeout, push-pull active-high RESET output, -40°C to +85°C operating range, and compatibility with low-voltage µP systems requiring guaranteed reset assertion below 1.2V.

Technical Context

The MAX6855UK21D1+T implements a precision bandgap-based voltage monitor with ±2.5% threshold accuracy over temperature and a dedicated MR input with 10kΩ internal pullup and 1µs minimum pulse width support. Its reset logic guarantees deassertion only after VCC exceeds the 2.100V threshold *and* remains stable for ≥10ms, with immunity to VCC transients ≤40µs at 100mV overdrive.

This variant belongs to the MAX6854–MAX6869 family but excludes watchdog timer (WDI) and CT select functionality. It delivers active-high push-pull RESET output referenced to VCC, enabling direct interface to µP reset inputs without external pullups, and maintains valid reset signaling down to VCC = +1.1V per specification.

Key Specifications

Pinout & Package

Package: 5-pin SOT23-5, surface-mount, lead-free (+T suffix), footprint compatible with industry-standard 5-pin SOT23 layouts.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TPS3837K21DBVR and ADM6805-21ARTZ-RL, the MAX6855UK21D1+T uniquely combines 170nA supply current, 10ms timeout, active-high push-pull output, and integrated MR - making it optimal for space-constrained, battery-critical medical and portable designs where minimal BOM count and lowest possible ICC are mandatory.

Availability

MAX6855UK21D1+T is available at Aetrix Electronics and suitable for glucose monitors, patient monitors, and portable audio devices requiring stable component supply, long-term lifecycle support, and guaranteed lead-free compliance.

Supply support for MAX6855UK21D1+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 product line was designed specifically for ultra-low-power microprocessor supervision in battery-operated medical and portable equipment, emphasizing sub-µA quiescent current and guaranteed operation down to 1.1V.

FAQ

What is the exact reset threshold voltage of the MAX6855UK21D1+T?

The MAX6855UK21D1+T has a factory-trimmed reset threshold voltage of 2.100V, with ±2.5% tolerance over the full -40°C to +85°C temperature range. This value is confirmed in Table 2 (Threshold Suffix Guide) of the datasheet, where suffix "21" corresponds to 2.100V nominal. The device asserts reset when VCC falls below this threshold and holds reset for the full 10ms timeout after VCC rises above it.

Does the MAX6855UK21D1+T include a watchdog timer function?

No, the MAX6855UK21D1+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 timer capability is exclusive to MAX6864–MAX6869 variants, identifiable by "S" or "L" suffixes in the ordering code. The MAX6855UK21D1+T pinout lacks WDI, confirming absence of watchdog circuitry.

What is the function of Pin 1 and Pin 4 on the MAX6855UK21D1+T?

On the MAX6855UK21D1+T, Pin 1 is the active-high push-pull RESET output, and Pin 4 is a second ground (GND) terminal - electrically tied to Pin 2 internally. This dual-GND configuration improves noise immunity and thermal performance in compact SOT23 layouts. Pin 1 drives high when VCC is valid and the reset timeout expires; Pin 4 must be soldered to the PCB ground plane alongside Pin 2 for proper operation.

Can the MAX6855UK21D1+T operate from a 1.5V supply?

Yes, the MAX6855UK21D1+T operates from 1.2V to 5.5V, so it functions reliably at 1.5V. However, its reset threshold is fixed at 2.100V - meaning it will assert reset continuously when supplied from 1.5V, as VCC never reaches the threshold. It is intended to monitor a higher-voltage rail (e.g., 3.3V or 2.5V) while being powered from that same rail, not to regulate or bootstrap from sub-threshold supplies.

Is the MAX6855UK21D1+T pin-compatible with other MAX68xx supervisory ICs?

The MAX6855UK21D1+T shares the same 5-pin SOT23-5 package and pinout (RESET, GND, MR, GND, VCC) with MAX6854, MAX6856, MAX6861–MAX6863, and MAX6864–MAX6869 variants. However, functional compatibility depends on reset polarity and features: MAX6855 provides active-high push-pull RESET, whereas MAX6854 is active-low and MAX6856 is open-drain. Direct substitution requires matching output type and feature set.