Analog Devices Inc./Maxim Integrated MAX6865UK25D4L+T

Overview

The MAX6865UK25D4L+T from Maxim Integrated is a nanopower microprocessor supervisory circuit in a 5-pin SOT23 package, combining voltage monitoring, manual reset input (MR), and watchdog timer (WDI) functions. It asserts an active-low push-pull RESET output when VCC drops below 2.500V (±2.5%), MR is pulled low, or the watchdog expires after 209s (typ). Designed for ultra-low-power systems, it draws only 170nA (typ) at 2.5V and guarantees valid reset down to VCC = +1.1V.

For engineers reviewing the MAX6865UK25D4L+T datasheet, MAX6865UK25D4L+T pinout, MAX6865UK25D4L+T application, or MAX6865UK25D4L+T equivalent, key selection criteria include its factory-trimmed 2.5V reset threshold, 1200ms minimum reset timeout (D4), long watchdog period (L = 209s typ), push-pull active-low RESET output, and immunity to short VCC transients - critical for battery-powered medical and portable electronics.

Technical Context

This device implements a precision bandgap-based voltage monitor with 2.5% threshold tolerance and 0.5% hysteresis, paired with a temperature-stable RC-based watchdog timer. The internal 10kΩ MR pullup enables direct switch interfacing without external components, while the WDI input detects edges ≥150ns to clear the watchdog counter.

Reset assertion is synchronized to VCC crossing the threshold, followed by a guaranteed minimum 1200ms timeout (D4 option) before deassertion. The push-pull RESET output drives low to ≤0.3V at 1.2mA sink current (VCC ≥ 2.38V) and high to ≥0.8×VCC at 500µA source current - ensuring robust logic-level compatibility across 1.2V–5.5V supply rails.

Key Specifications

Pinout & Package

Package: 5-pin SOT23-5, lead-free (RoHS-compliant), 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 MAX6864UK25D4L+T, the MAX6865UK25D4L+T offers identical core supervision but differs in pinout (RESET on Pin 1 vs. Pin 4), making it non-drop-in; versus TPS3838K25DBVR, it adds watchdog capability and push-pull drive - enabling simpler, more reliable system-level fault recovery.

Availability

MAX6865UK25D4L+T is available at Aetrix Electronics and suitable for glucose monitors, patient monitors, smart pagers, and industrial handheld terminals requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for MAX6865UK25D4L+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 timing applications, with emphasis on low-power, high-reliability solutions for medical and portable electronics.

The MAX6854–MAX6869 family delivers nanopower supervisory circuits targeting battery-critical systems where extended runtime, deterministic reset behavior, and integrated watchdog protection are mandatory design requirements.

FAQ

What is the exact reset threshold voltage for MAX6865UK25D4L+T?

The MAX6865UK25D4L+T has a factory-trimmed reset threshold of 2.500V with ±2.5% tolerance over -40°C to +85°C. This value is confirmed in Table 2 (Threshold Suffix Guide) of the datasheet, where suffix "25" corresponds to 2.500V nominal. The device guarantees valid reset assertion down to VCC = +1.1V, supporting robust brownout detection in low-voltage systems.

Does MAX6865UK25D4L+T include a watchdog timer, and what is its timeout?

Yes, the MAX6865UK25D4L+T includes a watchdog timer with a typical timeout of 209 seconds, indicated by the "L" suffix in the part number. This long timeout is optimized for firmware with extended idle or calibration phases. The watchdog clears on any rising or falling edge at the WDI pin and triggers reset if WDI remains static beyond the timeout period - a behavior verified in the Electrical Characteristics table and Figure 3 of the datasheet.

What type of RESET output does MAX6865UK25D4L+T provide?

The MAX6865UK25D4L+T provides a push-pull active-low RESET output on Pin 1. Unlike open-drain variants, this configuration eliminates the need for an external pullup resistor and ensures strong logic-level drive: VOL ≤ 0.3V at 1.2mA sink (VCC ≥ 2.38V) and VOH ≥ 0.8×VCC at 500µA source. This is explicitly defined in the MAX6864/MAX6865/MAX6866 Pin Description section.

How is the 1200ms reset timeout implemented in MAX6865UK25D4L+T?

The MAX6865UK25D4L+T implements a fixed 1200ms minimum reset timeout, denoted by the "D4" suffix. Per Table 4, D4 specifies 1200ms (min), 1800ms (typ), and 2400ms (max) timeout values. This internal timer begins counting after VCC rises above the 2.5V threshold *and* MR is deasserted, ensuring the µP receives a clean, extended reset pulse - a timing relationship confirmed in Figure 2 and the Detailed Description section.

Is MAX6865UK25D4L+T pin-compatible with other devices in the MAX68xx family?

No, MAX6865UK25D4L+T is not universally pin-compatible across the MAX68xx family. While all variants use the 5-pin SOT23 package, pin assignments differ: MAX6865UK25D4L+T places RESET on Pin 1, MR on Pin 3, and WDI on Pin 4. In contrast, MAX6867 places WDI on Pin 1 and RESET on Pin 4. These differences are documented in the Pin Configurations and Selector Guide - confirming that substitution requires PCB layout review.