Analog Devices Inc./Maxim Integrated MAX691ACUE+

Overview

MAX691ACUE+ from Maxim Integrated is a microprocessor supervisory circuit providing power-on reset, watchdog timer, battery switchover, and chip-enable gating for 5V systems. It features a 4.65V typical reset threshold, 200ms reset timeout, 30μA operating supply current, and guaranteed RESET assertion down to VCC = 1V. It is used in embedded controllers and intelligent instruments requiring reliable power monitoring and data retention during brownout.

For engineers reviewing the MAX691ACUE+ datasheet, MAX691ACUE+ pinout, MAX691ACUE+ application, or MAX691ACUE+ equivalent, key selection criteria include reset threshold accuracy (±150mV), battery switchover hysteresis (60mV), CE propagation delay (6–10ns), and dual RESET/RESET outputs with open-drain and active-high configurations.

Technical Context

The MAX691ACUE+ integrates a precision voltage monitor, internal oscillator-based reset and watchdog timing, and bidirectional power-path control between VCC and VBATT. Its reset generator asserts both active-low RESET and active-high RESET outputs synchronously upon VCC crossing 4.65V ±150mV, with 200ms typ timeout after power-up.

It implements chip-enable gating via a 75Ω series transmission gate (CE IN → CE OUT) with sub-10ns propagation delay, and supports watchdog timeout selection via OSC SEL/OSC IN - enabling fixed 100ms/1.6s modes or capacitor-programmable periods. Battery switchover occurs when VCC falls below VBATT − 0.3V (power-down) or rises above VBATT + 0.3V (power-up), with 60mV hysteresis.

Key Specifications

Pinout & Package

MAX691ACUE+ is housed in a 16-pin TSSOP package (3.0mm × 4.4mm, 0.65mm pitch), optimized for space-constrained industrial and instrumentation PCBs.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX691ACUE+, MAX693ACSE+ offers identical functionality with lower reset threshold for stricter brownout response, while TPS3808G33DBVR provides basic 3.3V supervision without backup or bus-gating - making MAX691ACUE+ uniquely suitable for 5V industrial controllers needing integrated power-path control.

Availability

MAX691ACUE+ is available at Aetrix Electronics and suitable for industrial controllers, intelligent instruments, critical μP power monitoring, and embedded computers requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for MAX691ACUE+ 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, automotive, and communications applications.

The MAX691A family was designed specifically for robust 5V microprocessor supervision - integrating reset generation, watchdog monitoring, battery switchover, and chip-enable gating in a single TSSOP package for space-constrained embedded systems.

FAQ

What is the reset threshold voltage of the MAX691ACUE+ and how tightly is it specified?

The MAX691ACUE+ has a typical reset threshold voltage of 4.65V, with a guaranteed range of 4.50V to 4.75V across temperature and supply variations. This specification ensures deterministic reset assertion during 5V system brownout events, and is validated per the MAX691A datasheet Electrical Characteristics table under "Reset Threshold Voltage" for MAX691A/MAX800L variants.

Does the MAX691ACUE+ support battery backup, and what are the voltage and current limits?

Yes, the MAX691ACUE+ supports battery backup via the VBATT pin, switching to battery power when VCC falls below VBATT − 0.3V. It accepts VBATT from 2.0V to 5.5V, delivers up to 25mA continuous current from VBATT, and maintains VOUT regulation with ≤150mV drop at 5mA load. The switchover hysteresis is 60mV to prevent chatter.

How does the MAX691ACUE+ implement chip-enable gating, and what is its timing impact?

The MAX691ACUE+ gates CE signals using a 75Ω series transmission gate between CE IN and CE OUT, with a maximum propagation delay of 10ns (tested at 50Ω drive, 50pF load). During reset assertion, CE IN is placed in high-impedance state and CE OUT is pulled high, preventing spurious writes to CMOS RAM - a key feature confirmed in the "Chip-Enable Signal Gating" section of the datasheet.

Can the watchdog timeout period of the MAX691ACUE+ be adjusted, and how?

Yes, the MAX691ACUE+ watchdog timeout is configurable: floating OSC SEL selects 1.6s nominal timeout; tying OSC SEL to GND enables external timing via OSC IN (capacitor or clock). With OSC SEL = GND and 47pF on OSC IN, long timeout is ~1.6s and short timeout is ~100ms. These modes are documented in Table 1 ("Reset Pulse Width and Watchdog Timeout Selections") of the MAX691A datasheet.

What is the difference between the RESET and RESET outputs on the MAX691ACUE+?

RESET is an active-low, open-drain output that sinks current when asserted; RESET is its active-high, open-drain complement - high-impedance when asserted, pulled to VOUT when deasserted. Both are synchronized and asserted simultaneously during reset events. This dual-output architecture allows direct interfacing with μPs requiring either reset polarity, as detailed in the "RESET and RESET Outputs" section of the MAX691A datasheet.