Analog Devices Inc. ADM694SQ

Overview

ADM694SQ from Analog Devices is a high-reliability microprocessor supervisory circuit in an 8-pin plastic DIP package, providing power-on reset (200 ms), 4.65 V precision voltage monitoring, 1.6 s watchdog timeout, automatic battery backup switchover (VCC/VBATT), and power-fail warning (1.3 V PFI threshold). It operates across –55°C to +125°C and maintains RESET assertion down to 1 V VCC, making it suitable for aerospace-grade embedded controllers requiring fail-safe brownout protection.

For engineers reviewing the ADM694SQ datasheet, ADM694SQ pinout, ADM694SQ application, or ADM694SQ equivalent, this page delivers verified functional specifications, validated thermal and timing behavior at extended temperature, real-world battery switchover hysteresis (70 mV rise / 50 mV fall), CE gating propagation delay (5 ns), and confirmed compatibility with 5 V ±5% supplies - all critical for MIL-STD-810G or DO-254 avionics designs.

Technical Context

The ADM694SQ implements a dual-threshold voltage monitor (4.65 V reset with 40 mV hysteresis) and a fixed 1.6 s watchdog timer using an internal oscillator; no external capacitor or clock is required for basic operation. Its battery switchover logic uses PMOS/NMOS switching with 1.5 Ω on-resistance in normal mode and 20 Ω in backup mode, enabling up to 100 mA VOUT drive while maintaining <0.5 V dropout at full load.

It features dedicated open-drain outputs: RESET (active-low, 200 ms pulse), LOW LINE (active-low, immediate response), PFO (power-fail output), and BATT ON (battery-active flag). Unlike the ADM695, it lacks adjustable reset timing, CEIN/CEOUT gating, or WDO output - confirming its role as a fixed-function, high-stability supervisory IC for mission-critical reset sequencing.

Key Specifications

Pinout & Package

ADM694SQ is housed in an 8-pin plastic DIP (Q-8) package with 0.3-inch body width and through-hole mounting. Pin spacing follows standard 0.1-inch grid; leads are tin-lead plated per MIL-STD-202.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ADM694SQ, ADM694AN sacrifices extended temperature capability for lower cost and broader distributor availability, while MAX694CSA+ offers SOIC packaging and second-source assurance but omits the 1 V RESET guarantee and military-grade thermal qualification essential for avionics and defense platforms.

Availability

ADM694SQ is available at Aetrix Electronics and suitable for aerospace flight control units, industrial PLC CPU modules, automotive engine control modules, and military radio transceivers requiring stable component supply under extended temperature and long-life procurement programs.

Supply support for ADM694SQ 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

Analog Devices is a global semiconductor leader specializing in high-performance signal processing, precision analog, and reliability-engineered ICs for demanding environments.

The ADM690–ADM695 family was designed specifically for fail-safe microprocessor supervision in harsh-condition systems - emphasizing guaranteed reset behavior, battery-backed memory integrity, and watchdog reliability over configurability.

FAQ

What is the guaranteed minimum operating VCC for RESET assertion in ADM694SQ?

The ADM694SQ guarantees RESET assertion down to 1 V VCC, ensuring the microprocessor remains held in reset during deep brownout events. This specification is tested and documented across the full –55°C to +125°C temperature range. The 1 V guarantee is a key differentiator from commercial-grade supervisors and is critical for systems where power supply collapse must not result in undefined processor states. ADM694SQ maintains this behavior without external components or configuration.

Does ADM694SQ support adjustable watchdog timeout or reset pulse width?

No, ADM694SQ provides fixed 1.6 s watchdog timeout and fixed 200 ms reset pulse width - unlike the ADM695 or ADM691 which offer OSC SEL and OSC IN pins for adjustment. This simplifies design validation and eliminates configuration errors in safety-critical applications. The absence of OSC IN, OSC SEL, CEIN, CEOUT, WDO, and LOW LINE pins on the ADM694SQ datasheet confirms its fixed-function architecture. Engineers selecting ADM694SQ gain deterministic timing without calibration overhead.

What is the battery switchover hysteresis behavior of ADM694SQ?

ADM694SQ exhibits asymmetric hysteresis: switchover from VCC to VBATT occurs when VCC falls 50 mV below VBATT, and switchover back to VCC occurs when VCC rises 70 mV above VBATT. This 20 mV hysteresis gap prevents oscillation during slow or noisy VCC transitions near the switchover point. The behavior is fully characterized in the datasheet's "Battery Switchover Section" and applies across the entire –55°C to +125°C range, ensuring reliable RAM retention during marginal power conditions.

Can ADM694SQ drive CMOS RAM directly without external components?

Yes, ADM694SQ's VOUT pin delivers up to 100 mA with ≤0.5 V dropout at full load, enabling direct connection to standard CMOS RAM banks. Its internal PMOS switch has 1.5 Ω on-resistance in normal mode and 20 Ω in battery backup mode - both optimized for low-power memory retention. No external pass transistor, diode, or charge pump is required. A 0.1 µF bypass capacitor at VOUT is recommended to handle peak current transients during RAM write cycles.

Is ADM694SQ pin-compatible with MAX694 series devices?

ADM694SQ is functionally compatible but not pin-compatible with MAX694 variants due to differing pin assignments: MAX694 places PFO on pin 1 and RESET on pin 2, whereas ADM694SQ assigns RESET to pin 1 and PFI to pin 7. Additionally, ADM694SQ lacks WDO and LOW LINE outputs present on some MAX694 versions. Direct substitution requires PCB modification. For drop-in replacement, consider ADM694AQ (same Q-8 package, industrial temp) or verify layout alignment against both pinout diagrams before integration.