Analog Devices Inc. ADM691AQ

Overview

ADM691AQ from Analog Devices is a 16-pin DIP microprocessor supervisory circuit providing precision reset generation (4.65 V threshold), adjustable watchdog timeout (100 ms / 1.6 s / user-configurable), automatic battery backup switchover (VCC/VBATT), CE signal gating (5 ns propagation), and power-fail warning (1.3 V PFI comparator) for industrial embedded systems operating from –40°C to +85°C.

For engineers reviewing the ADM691AQ datasheet, ADM691AQ pinout, ADM691AQ application, or ADM691AQ equivalent, this device supports critical power-monitoring tasks in automotive controllers, industrial PLCs, and intelligent instrumentation where reliable brownout detection, RAM write protection, and fail-safe shutdown sequencing are required.

Technical Context

The ADM691AQ integrates a precision 4.65 V reset voltage detector with 40 mV hysteresis, an internal oscillator selectable between 100 ms and 1.6 s watchdog periods (or externally adjustable via OSC IN/OSC SEL), and dual-mode battery switchover logic that transitions at VCC–VBATT = 70 mV (rising) and 50 mV (falling) with 20 mV hysteresis.

It features three dedicated outputs-BATT ON (35 mA sink), LOW LINE (active-low VCC monitor), and WDO (watchdog status)-plus CEIN/CEOUT gating with 5 ns delay and guaranteed operation down to VCC = 1 V, enabling robust system-level power integrity control without external components.

Key Specifications

Pinout & Package

ADM691AQ is housed in a 16-pin plastic DIP (Q-16) package with 0.3-inch body width and standard through-hole mounting. Pin spacing conforms to JEDEC MS-001.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX691CPD+ and TPS3823MPW, the ADM691AQ uniquely combines adjustable watchdog timing, CE signal gating, and battery switchover in a single 16-pin DIP-making it irreplaceable in legacy industrial systems requiring coordinated power, memory, and fail-safe control.

Availability

ADM691AQ is available at Aetrix Electronics and suitable for industrial PLC controllers, automotive engine control units, medical diagnostic instruments, and telecom base station controllers requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for ADM691AQ 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 leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, serving industrial, automotive, communications, and healthcare markets since 1965.

The ADM691AQ belongs to the ADM690–ADM695 family of microprocessor supervisory circuits, engineered specifically for robust power monitoring, battery backup management, and system-level fault containment in mission-critical embedded systems.

FAQ

What is the guaranteed reset voltage threshold range for ADM691AQ?

The ADM691AQ has a guaranteed reset voltage threshold range of 4.50 V to 4.73 V at +25°C, with 40 mV hysteresis. This ensures compatibility with +5 V ±5% power supplies and guarantees reliable reset assertion during brownout conditions across the full –40°C to +85°C operating range. The ADM691AQ maintains functional reset output down to VCC = 1 V, making it suitable for deep undervoltage shutdown sequencing.

How does ADM691AQ handle battery switchover during slow VCC decay?

The ADM691AQ uses asymmetric switchover thresholds: VCC must exceed VBATT by 70 mV to switch from battery to main supply (power-up), and VCC must fall 50 mV below VBATT to switch from main to battery (power-down). This 20 mV hysteresis prevents oscillation during slow VCC decay near VBATT voltage, ensuring clean, chatter-free transitions critical for RAM data retention. The ADM691AQ also draws only 1 µA in battery-backup mode.

Can ADM691AQ drive external circuitry beyond its 100 mA VOUT limit?

Yes-the ADM691AQ includes a dedicated BATT ON output capable of sinking 35 mA, which can directly drive the base of an external PNP transistor to extend VOUT current beyond 100 mA. This allows high-current backup for larger SRAM banks or EEPROMs without compromising the ADM691AQ's internal switch integrity. The ADM691AQ's BATT ON logic is asserted only when VOUT is sourced from VBATT, enabling precise external pass transistor control.

What are the valid configurations for adjusting watchdog timeout on ADM691AQ?

The ADM691AQ supports three watchdog timeout modes: (1) OSC SEL high/floating + OSC IN high → 1.6 s; (2) OSC SEL high/floating + OSC IN low → 100 ms; (3) OSC SEL low + external clock (0–250 kHz) or capacitor (e.g., 47 pF → 1.04 s) on OSC IN. Immediately after any reset, the timeout defaults to 1.6 s regardless of configuration-ensuring safe microprocessor initialization before short-period supervision begins.

Does ADM691AQ provide both active-high and active-low reset outputs?

Yes-the ADM691AQ provides two complementary reset outputs: RESET (active-low) and RESET (active-high). Both are fully buffered and synchronized; RESET asserts low when VCC falls below 4.65 V, watchdog expires, or VCC drops below VBATT, while RESET asserts high under identical conditions. This eliminates the need for external inverters when interfacing with processors requiring either polarity, and both outputs remain functional down to VCC = 1 V.