Analog Devices Inc./Maxim Integrated MAX691CWE+

Overview

The MAX691CWE+ from Maxim Integrated is a 16-pin microprocessor supervisory circuit providing reset generation, battery backup switchover, adjustable watchdog timer, power-fail detection, and CE gating for CMOS RAM. It features a 4.65V reset threshold, 200ms reset timeout, 1.6s/100ms selectable watchdog period, 1.3V PFI comparator, and VOUT switching between VCC and VBATT. It is used in industrial controllers and intelligent instruments requiring reliable power monitoring and data retention during brownouts.

For engineers reviewing the MAX691CWE+ datasheet, MAX691CWE+ pinout, MAX691CWE+ application, or MAX691CWE+ equivalent, key selection considerations include its 16-pin SOIC-W package, dual active-low/high RESET outputs, BATT ON and WDO signals, CE IN/OUT write protection logic, and compatibility with 5V ±5% supplies and 2.0–4.25V backup batteries.

Technical Context

The MAX691CWE+ integrates five core supervisory functions: precision voltage monitoring (4.65V ±150mV threshold), programmable reset timing (200ms default), dual-mode watchdog (internal oscillator or external clock input), battery switchover with 70mV rise/50mV fall hysteresis, and chip-enable gating that forces CE OUT high when VCC drops below 4.65V. Its internal 1.3V reference drives the PFI comparator for early power-fail warning.

It operates across 0°C to +70°C (C-suffix), uses an internal 6.55kHz oscillator when OSC SEL is floating, and supports external timing via OSC IN (0–250kHz) or capacitor-based frequency adjustment. The BATT ON output sinks 25mA to drive external PNP transistors, while VOUT delivers up to 50mA from VCC or VBATT with <1µA standby current in battery-backup mode.

Key Specifications

Pinout & Package

MAX691CWE+ is housed in a 16-pin wide-body SOIC (SOIC-W) package, 7.5mm body width, 1.27mm pitch, RoHS-compliant, rated for 0°C to +70°C operation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX691CSA+ and TPS3823MPW, the MAX691CWE+ uniquely combines 16-pin feature density-including dual RESET, CE gating, BATT ON, WDO, and programmable timing-enabling single-chip supervision for complex embedded systems where data integrity and fail-safe restart are mandatory.

Availability

MAX691CWE+ is available at Aetrix Electronics and suitable for industrial controllers, automotive body modules, medical infusion pumps, test equipment, and critical µP power monitoring requiring stable component supply over extended production lifecycles.

Supply support for MAX691CWE+ 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, mixed-signal, and power management ICs for industrial, automotive, communications, and computing markets.

The MAX690–MAX695 family was engineered specifically for microprocessor-based systems needing integrated power supervision, battery backup, and data integrity protection in space-constrained, reliability-critical applications.

FAQ

What is the reset threshold voltage of the MAX691CWE+ and how tightly is it specified?

The MAX691CWE+ has a guaranteed reset threshold of 4.65V, with a minimum of 4.5V and maximum of 4.75V across the full operating temperature range (0°C to +70°C). This ±150mV tolerance ensures robust operation with standard 5V ±5% power supplies, preventing spurious resets during nominal ripple or transient excursions while asserting reset before microprocessor functional failure.

How does the MAX691CWE+ handle battery backup switchover, and what is the hysteresis?

The MAX691CWE+ compares VCC and VBATT internally and connects VOUT to the higher supply. Switchover occurs at VCC − VBATT = +70mV during power-up and +50mV during power-down, with 20mV hysteresis to prevent oscillation near the crossover point. This ensures clean, glitch-free handover to backup battery during brownouts, preserving CMOS RAM data without interruption.

Can the MAX691CWE+ watchdog timer be disabled, and how?

Yes, the MAX691CWE+ watchdog timer is disabled when the WDI pin is left floating or driven to mid-supply (~38% of VCC). The internal 125kΩ bias network pulls WDI to this level, placing the watchdog in inactive state. No external components are required-simply omit connection to WDI or tie it through a high-value resistor (e.g., 1MΩ) to VCC/2 to disable supervision.

What is the purpose of the CE IN and CE OUT pins on the MAX691CWE+, and how do they protect RAM?

The CE IN and CE OUT pins implement hardware write protection: CE OUT follows CE IN only when VCC ≥ 4.65V; if VCC drops below threshold, CE OUT is forced high regardless of CE IN state. This disables chip enable to battery-backed CMOS RAM during brownouts, preventing erroneous writes caused by marginal µP operation-ensuring data integrity without software intervention.

Does the MAX691CWE+ support external timing sources, and how is it configured?

Yes, the MAX691CWE+ supports external timing via the OSC SEL and OSC IN pins. When OSC SEL is pulled low, OSC IN accepts an external clock (0–250kHz) or a capacitor (e.g., 47pF to GND) to set both reset timeout and watchdog period. Configuration table in datasheet defines exact timing values-e.g., 47pF yields ~1.6s watchdog with OSC SEL low-enabling precise adaptation to system firmware timing requirements.