Analog Devices Inc./Maxim Integrated MAX6855UK39D3+T

Overview

MAX6855UK39D3+T from Maxim Integrated is a nanopower microprocessor supervisory circuit in 5-pin SOT23 package, featuring active-high push-pull reset output, 3.9V factory-trimmed reset threshold (±2.5%), 150ms minimum reset timeout, and manual reset input. It monitors VCC for brownout detection down to 1.1V and asserts reset during power-up, power-down, or MR assertion - used in battery-powered glucose monitors and portable medical devices.

For engineers reviewing the MAX6855UK39D3+T datasheet, MAX6855UK39D3+T pinout, MAX6855UK39D3+T application, or MAX6855UK39D3+T equivalent, key selection criteria include ultra-low 170nA supply current, guaranteed reset validity at VCC = 1.1V, immunity to short VCC transients (<40µs at 100mV overdrive), and compatibility with CMOS-level MR input and push-pull RESET logic interface.

Technical Context

The MAX6855UK39D3+T implements a precision voltage monitor with hysteresis (0.5% of VTH) and an internal timer that holds RESET asserted for ≥150ms after VCC exceeds 3.9V and MR deasserts. Its active-high push-pull output is referenced to VCC and sinks ≤0.3V at 1.2mA load, enabling direct interfacing with µP reset inputs requiring high-true assertion.

No watchdog timer or CT pin functionality is present - this variant belongs to the MAX6855 subgroup defined by active-high RESET, MR input, and fixed D3 (150ms) timeout. It shares pinout and electrical behavior with MAX6854/MAX6856 but differs in reset polarity and output configuration.

Key Specifications

Pinout & Package

Package: 5-pin SOT23-5, lead-free, -40°C to +85°C operating range.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TPS3837K33DBVR and MAX6316LUK39D3+T, the MAX6855UK39D3+T uniquely combines ultra-low 170nA ICC, active-high push-pull RESET, and integrated MR - making it optimal for long-life, manually resettable medical and portable electronics where layout area and power budget are critical.

Availability

MAX6855UK39D3+T is available at Aetrix Electronics and suitable for glucose monitors, patient monitoring devices, and MP3 players requiring stable component supply with long-term lifecycle support and lead-free compliance.

Supply support for MAX6855UK39D3+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, sensing, and interface applications in industrial, medical, and consumer systems.

The MAX6855UK39D3+T belongs to the nanopower µP supervisory family engineered specifically for battery-critical portable medical and handheld electronics - emphasizing sub-µA quiescent current, wide VCC range, and robust transient immunity.

FAQ

What is the exact reset threshold voltage of the MAX6855UK39D3+T?

The MAX6855UK39D3+T has a factory-trimmed reset threshold of 3.900V with ±2.5% tolerance over temperature (-40°C to +85°C). This value is confirmed in Table 2 (Threshold Suffix Guide) of the datasheet, where suffix "39" corresponds to 3.900V nominal. The device guarantees reset assertion when VCC falls below this threshold and remains asserted until VCC exceeds 3.900V + hysteresis (0.5% of VTH) and the 150ms timeout expires. The MAX6855UK39D3+T uses this precise threshold to protect 3.3V systems against brownout while maintaining sufficient margin above LDO dropout.

Does the MAX6855UK39D3+T include a watchdog timer function?

No, the MAX6855UK39D3+T does not include a watchdog timer. It belongs to the MAX6855 subgroup, which provides only voltage monitoring and manual reset (MR) functionality - as confirmed in the Selector Guide (page 16) and Pin Description (page 7). Watchdog capability is exclusive to MAX6864–MAX6869 variants, identifiable by the "S" or "L" suffix in the ordering code. The MAX6855UK39D3+T relies solely on VCC supervision and MR input for reset generation, making it suitable for simpler systems where software execution monitoring is handled externally or not required.

What is the function of Pin 1 on the MAX6855UK39D3+T?

Pin 1 of the MAX6855UK39D3+T is the RESET output terminal, configured as an active-high push-pull driver. When asserted (during VCC brownout or MR activation), it drives high to the VCC rail; when deasserted, it pulls low. This eliminates the need for an external pullup resistor and enables direct connection to µP reset pins requiring high-true logic. The pin's VOH is guaranteed ≥0.8×VCC at 200µA source current, and VOL ≤0.3V at 1.2mA sink current - specifications verified in the Electrical Characteristics table (page 3). This behavior is specific to the MAX6855 variant and differs from MAX6854 (active-low push-pull) and MAX6856 (active-low open-drain).

Can the MAX6855UK39D3+T operate with a 1.8V supply?

Yes, the MAX6855UK39D3+T operates with VCC as low as 1.2V and guarantees valid reset assertion down to VCC = 1.1V - confirmed in Absolute Maximum Ratings and Electrical Characteristics (page 2). At 1.8V supply, its typical supply current is 170nA, and RESET output maintains full logic swing (VOH ≥1.44V, VOL ≤0.3V). However, the 3.9V reset threshold means it will assert reset immediately at 1.8V - so this part is intended for monitoring higher rails (e.g., 3.3V or 3.6V supplies), not 1.8V domains. The MAX6855UK39D3+T is designed to supervise systems where VCC is ≥3.3V; using it on 1.8V violates its functional voltage monitoring intent.

Is the MAX6855UK39D3+T pin-compatible with other MAX68xx supervisory ICs?

The MAX6855UK39D3+T shares the same 5-pin SOT23-5 package and pinout (RESET, GND, MR, GND, VCC) with MAX6854, MAX6856, MAX6861–MAX6863, and MAX6864–MAX6869 - confirmed in Pin Configurations (page 15) and Selector Guide (page 16). However, pin compatibility does not imply functional interchangeability: MAX6854 outputs active-low RESET, MAX6856 uses open-drain, and MAX6864 adds WDI. Substituting without verifying reset polarity, output type, and feature set may cause system failure. The MAX6855UK39D3+T is functionally compatible only with other MAX6855 variants sharing the same suffixes (e.g., MAX6855UK39D2+T differs only in timeout).