Analog Devices Inc./Maxim Integrated MAX691MJE

Overview

MAX691MJE from Maxim Integrated is a 16-pin microprocessor supervisory circuit providing reset generation, battery backup switchover, watchdog timer, power-fail detection, and CE gating for CMOS RAM/EEPROM - with 4.65V reset threshold, 1.6s fixed watchdog timeout, 200ms reset pulse width, and 1µA battery-backup supply current. It is used in automotive control units to maintain RAM integrity during ignition cycling.

For engineers reviewing the MAX691MJE datasheet, MAX691MJE pinout, MAX691MJE application, or MAX691MJE equivalent, key selection considerations include its M-suffix military temperature range (–55°C to +125°C), 16-pin CERDIP package, VCC/VBATT switchover hysteresis of 20mV, CE OUT logic-controlled write protection, and compatibility with 2.0V–4.25V backup batteries.

Technical Context

The MAX691MJE integrates five core supervisory functions: a precision 4.65V reset comparator with 40mV hysteresis, a fixed 1.6s watchdog timer with WDI transition detection, a 1.3V PFI comparator for power-fail or low-battery warning, internal VCC/VBATT switchover with 70mV turn-on/50mV turn-off thresholds, and CE IN/CE OUT gating that forces CE OUT high when VCC drops below 4.65V.

Its dual-output RESET (active-low) and RESET (active-high), plus dedicated WDO and BATT ON outputs, enable direct interface to µP NMI lines, external PNP pass transistors, and system status indicators - all while maintaining 1µA max quiescent current in battery-backup mode with VCC = 0V and VBATT = 2.8V.

Key Specifications

Pinout & Package

MAX691MJE is supplied in a 16-pin hermetically sealed CERDIP package (package code MJE), rated for military-grade thermal and mechanical reliability. Pin assignments are fully defined per Maxim's official pinout diagram for MAX691/MAX693/MAX695.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX695MJE and MAX791MJE, the MAX691MJE delivers deterministic 200ms reset timing and ultra-low 1µA battery drain without external timing components or charge-pump overhead - making it ideal for mission-critical, maintenance-free embedded systems requiring guaranteed RAM retention over decades.

Availability

MAX691MJE is available at Aetrix Electronics and suitable for automotive engine control, avionics data logging, and industrial PLC I/O modules requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for MAX691MJE 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 demanding industrial, automotive, and communications applications.

The MAX690–MAX695 family was engineered specifically for microprocessor system supervision - integrating reset, watchdog, battery switchover, power-fail detection, and memory write protection into single-chip solutions for safety-critical embedded platforms.

FAQ

What is the operating temperature range of the MAX691MJE?

The MAX691MJE is specified for –55°C to +125°C operation (M-suffix), validated per MIL-STD-883 test methods. This full military temperature range ensures reliable performance in under-hood automotive ECUs, aerospace data loggers, and industrial controllers exposed to extreme ambient conditions. The MAX691MJE maintains all electrical specifications - including 4.65V reset threshold and 1µA backup current - across this entire range.

Does the MAX691MJE support adjustable watchdog timeout periods?

No, the MAX691MJE features a fixed 1.6s watchdog timeout period. Unlike the MAX695MJE, which supports selectable 100ms/1.6s timeouts via OSC SEL and OSC IN pins, the MAX691MJE uses an internal oscillator with unadjustable timing. Its watchdog behavior is fully documented in the datasheet: WDI must be toggled at least once every 1.6s to prevent a 200ms RESET pulse. This fixed timing simplifies qualification for safety-critical applications where deterministic response is mandatory.

How does the CE OUT pin protect CMOS RAM during brownout events?

The MAX691MJE's CE OUT pin is designed to force CMOS RAM into read-only mode during voltage anomalies. When VCC drops below 4.65V, CE OUT is driven high regardless of CE IN state - disabling write access to RAM. This hardware-enforced gating occurs within 200ns, faster than most µP bus cycles, and remains active until VCC recovers above 4.75V. In the MAX691MJE, this function operates independently of the watchdog or reset state, ensuring data integrity even during partial power failures.

What is the maximum load current supported by the VOUT pin of the MAX691MJE?

The VOUT pin of the MAX691MJE delivers up to 50mA when powered from VCC, with a typical dropout voltage of 0.1V at 1mA and 0.5V at 50mA. During battery backup (VCC < VBATT), VOUT is sourced from a 200Ω internal MOSFET, supporting up to 250µA continuously while maintaining <100mV dropout. For loads exceeding 50mA, the MAX691MJE provides the BATT ON output to drive an external PNP transistor - enabling scalable current delivery while preserving the 1µA backup quiescent current specification.

Can the MAX691MJE be used with a 3.3V microprocessor system?

The MAX691MJE is designed for 5V systems and requires VCC = 4.75V–5.5V for full functionality; its 4.65V reset threshold and internal references assume a 5V nominal supply. While it can monitor a 3.3V rail via the PFI pin using a resistor divider, it cannot directly supervise or power a 3.3V µP core. For 3.3V systems, Maxim recommends the MAX6326 or MAX6369 families. The MAX691MJE's VOUT, RESET, and CE OUT outputs are 5V-tolerant but not 3.3V-compatible without level-shifting.