Analog Devices Inc./Maxim Integrated MAX691CPE

Overview

The MAX691CPE from Maxim Integrated is a 16-pin CMOS microprocessor supervisory circuit providing reset generation, battery backup switchover, watchdog timer, power-fail warning, and chip-enable gating for CMOS RAM/EEPROM. It features a 4.65V reset threshold, 200ms reset timeout, adjustable watchdog (100ms/1.6s), 1.3V PFI comparator, and VOUT switching between VCC and VBATT - used in industrial controllers and intelligent instruments requiring reliable power monitoring and data retention.

For engineers reviewing the MAX691CPE datasheet, MAX691CPE pinout, MAX691CPE application, or MAX691CPE equivalent, key selection considerations include its 16-pin PDIP package, active-low RESET with 200ms delay, CE OUT write-protection logic, BATT ON output for external transistor drive, and compatibility with 2.0V–4.25V backup batteries.

Technical Context

The MAX691CPE integrates five core supervisory functions: precision voltage monitoring (4.65V ±150mV reset threshold), dual-mode watchdog timer (internal oscillator or external clock input via OSC IN/OSC SEL), battery switchover with 70mV rising-edge and 50mV falling-edge hysteresis, 1.3V power-fail comparator referenced to PFI, and CE IN/CE OUT gating logic that forces CE OUT high during brownout to prevent erroneous RAM writes.

Its architecture includes an internal 6.55kHz oscillator, three-level WDI input (low/mid/high) enabling watchdog disable via floating state, and separate open-drain outputs: RESET (active-low), RESET (active-high), WDO, LOW LINE, BATT ON, and PFO - all with defined sink/source capabilities and timing relationships verified across 0°C to +70°C operation.

Key Specifications

Pinout & Package

MAX691CPE is supplied in a 16-pin plastic DIP (dual in-line package) with 0.3-inch body width and through-hole mounting. Pin 1 is top-left corner when notch faces up.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX691CPD and MAX693CPE, the MAX691CPE uniquely combines through-hole DIP packaging, 4.65V reset threshold for tighter 5V supply compliance, and full supervisory feature set - making it the preferred choice for industrial prototyping, field-replaceable modules, and designs requiring mechanical reliability over density.

Availability

MAX691CPE is available at Aetrix Electronics and suitable for industrial controllers, intelligent instruments, automotive body control modules, and critical µP power monitoring applications requiring stable component supply and long-term obsolescence management.

Supply support for MAX691CPE 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 computing applications.

The MAX690–MAX695 family was designed specifically to replace discrete reset/battery-switch/watchdog circuits in µP-based systems - delivering board-space savings, improved reliability, and guaranteed timing behavior under brownout conditions.

FAQ

What is the reset timeout delay of the MAX691CPE?

The MAX691CPE has a guaranteed reset timeout delay of 200ms after VCC rises above the 4.65V threshold. This delay is fixed and not adjustable - unlike the MAX690/MAX692 which use 50ms. The 200ms hold time ensures sufficient duration for microprocessor oscillator stabilization and firmware initialization before release from reset. This value is specified in the Electrical Characteristics table under "Reset Timeout Delay (MAX694/MAX695)" and applies identically to MAX691CPE as a member of the same variant group.

Does the MAX691CPE support battery backup for CMOS RAM?

Yes, the MAX691CPE supports battery backup for CMOS RAM via its VOUT pin, which automatically switches between VCC and VBATT based on relative voltage levels. When VCC drops below VBATT minus 70mV, the internal 200Ω MOSFET connects VBATT to VOUT, supplying power to RAM with typical dropout voltage under 100mV at 250µA. The MAX691CPE also provides BATT ON output to drive external PNP transistors for higher current demands, and draws only 1µA max in battery backup mode - ensuring multi-year retention with standard coin cells.

How does the CE OUT pin protect RAM during power failure?

The CE OUT pin of the MAX691CPE protects RAM by forcing a high logic level whenever VCC falls below the 4.65V reset threshold - regardless of the state of CE IN. This action disables the chip-enable signal to CMOS RAM or EEPROM, preventing any write operations during brownout, power-up, or momentary interruption. The propagation delay is 50ns typical, and the function operates independently of watchdog or reset timing. This hardware-enforced write protection eliminates reliance on firmware polling or external logic, ensuring data integrity even during catastrophic power events.

Can the watchdog timer on the MAX691CPE be disabled?

Yes, the watchdog timer on the MAX691CPE can be fully disabled by leaving the WDI (Watchdog Input) pin unconnected (floating). The datasheet confirms WDI is internally biased to ~38% of VCC with 125kΩ impedance, placing it in a mid-level inactive state that disables watchdog monitoring. No external pull-up or pull-down is required. Once disabled, WDO remains high and RESET will not assert due to watchdog timeout - though power-on and brownout reset functions remain fully operational. This provides design flexibility for systems where software-based supervision suffices.

What is the maximum backup battery voltage supported by the MAX691CPE?

The MAX691CPE supports a maximum backup battery voltage of 4.25V on the VBATT pin, as specified in the Electrical Characteristics table under "Operating Voltage Range (MAX690, MAX691, MAX694, MAX695 VBATT)". This limit applies across the full operating temperature range and ensures safe operation of the internal battery switchover MOSFET and comparator circuitry. Using a battery exceeding 4.25V - such as a fully charged 3.6V Li-ion cell - risks violating absolute maximum ratings and may cause permanent damage. Standard 3V lithium coin cells (e.g., CR2032, 2.0V–3.3V) are fully compatible.