Analog Devices Inc. ADM691AAN

Overview

ADM691AAN from Analog Devices is a microprocessor supervisory circuit integrating power-on reset, battery backup switchover, watchdog timer, chip enable gating, and power-fail detection. It features a 4.65 V ±3% reset threshold, 200 ms or adjustable reset timeout, 1.6 s/100 ms selectable watchdog timeout, and supports VCC down to 1 V operation. It is used in industrial controllers and automotive ECUs for reliable power monitoring and data retention during brownouts.

For engineers reviewing the ADM691AAN datasheet, ADM691AAN pinout, ADM691AAN application, or ADM691AAN equivalent, key selection criteria include its 4.65 V reset threshold compatibility with +5 V ±5% supplies, dual-mode watchdog (internal oscillator or external clock/capacitor), battery switchover with <1 µA standby current, and integrated CE gating for RAM write protection.

Technical Context

The ADM691AAN implements a precision bandgap-based voltage detector for reset generation, with hysteresis of 15 mV and guaranteed operation down to VCC = 1 V. Its internal PMOS VCC-to-VOUT switch exhibits 0.75 Ω typical on-resistance, while the VBATT-to-VOUT path uses a 7 Ω MOSFET optimized for low-current backup.

Watchdog timing is configurable via OSC SEL and OSC IN: floating OSC SEL enables internal oscillator modes (100 ms or 1.6 s), while grounded OSC SEL allows external capacitor (COSC) or clock input for adjustable timeouts - reset active period = 1200 × (C/47 pF) ms, watchdog = 600 × (C/47 pF) ms.

Key Specifications

Pinout & Package

ADM691AAN is packaged in a 16-pin plastic DIP (N-16) with 0.3-inch body width and standard through-hole mounting. Pin spacing is 0.1 inch, compatible with industry-standard PCB footprints and socketing.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX691ACPP+, ADM691AAN offers lower power and field-programmable timing; compared with TPS3823-46DBVR, it integrates battery management and watchdog functions that would otherwise require ≥3 discrete ICs, reducing design complexity and board space.

Availability

ADM691AAN is available at Aetrix Electronics and suitable for industrial PLCs, automotive body control modules, medical infusion pumps, and point-of-sale terminals requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for ADM691AAN 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 analog, mixed-signal, and digital signal processing technologies for precision measurement and control systems.

The ADM691AAN belongs to Analog Devices' microprocessor supervisory IC product line, designed specifically for robust power monitoring, data retention, and fault recovery in mission-critical embedded systems operating under harsh electrical and thermal conditions.

FAQ

What is the reset threshold voltage of the ADM691AAN?

The ADM691AAN has a guaranteed reset threshold of 4.65 V ±3%, with minimum and maximum limits of 4.5 V and 4.75 V respectively. This makes it compatible with +5 V power supplies having –5% to +10% tolerance. The threshold is internally generated using a precision bandgap reference and remains stable over temperature (–40°C to +85°C) and supply variations. The ADM691AAN datasheet specifies this value under TA = +25°C with hysteresis of 15 mV to prevent chatter near the trip point.

How does the ADM691AAN handle battery backup switchover?

The ADM691AAN automatically switches VOUT between VCC and VBATT based on relative voltage levels and reset state. When VCC exceeds VBATT + 0.03 V and remains above the 4.65 V reset threshold, VCC is routed to VOUT via a 0.75 Ω PMOS switch. When VCC falls below VBATT – 0.03 V and below reset threshold, VBATT is connected to VOUT through a 7 Ω MOSFET. Hysteresis of 60 mV prevents oscillation during slow transitions. In battery mode, supply current drops to 0.04 µA typical, enabling multi-year operation on CR2032 cells.

Can the watchdog timeout period of the ADM691AAN be adjusted?

Yes, the ADM691AAN watchdog timeout is fully configurable. With OSC SEL floating, grounding OSC IN selects 100 ms; leaving OSC IN floating selects 1.6 s. With OSC SEL grounded, an external capacitor (COSC) from OSC IN to GND sets timeout as T_wd = 600 × (C/47 pF) ms. An external clock applied to OSC IN yields T_wd = 1024 × (1/f_CLK). These adjustments apply to both watchdog and reset timeout periods, with reset = 2× watchdog period in capacitor/clock modes. All configurations are validated in the ADM691AAN datasheet.

What is the function of the CEOUT pin on the ADM691AAN?

The CEOUT pin on the ADM691AAN provides controlled gating of the chip enable (CE) or write (WR) signal to battery-backed CMOS RAM. During normal operation (VCC > 4.65 V), CEOUT is a buffered replica of CEIN with 5 ns propagation delay. When VCC drops below the reset threshold, CEOUT is forced high regardless of CEIN state - preventing accidental writes to RAM during power-up, brownout, or shutdown. This hardware-enforced write protection eliminates need for software-based memory lock routines and ensures data integrity without CPU intervention.

Does the ADM691AAN support power-fail warning before reset assertion?

Yes, the ADM691AAN includes a dedicated power-fail comparator with PFI input referenced to an internal 1.25 V precision bandgap. When the voltage at PFI falls below 1.25 V, PFO asserts low - typically used to trigger a non-maskable interrupt (NMI) in the microprocessor. Since PFI can be driven by a resistor divider from the unregulated input or regulated 5 V rail, PFO can activate several milliseconds before VCC reaches the 4.65 V reset threshold, providing critical time to save volatile data to non-volatile memory before system reset occurs.