Analog Devices Inc. ADM691AARNZ-REEL

Overview

ADM691AARNZ-REEL 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 fixed or adjustable reset timeout, 1.6 s/100 ms selectable watchdog timeout, 1.25 V PFI reference, and supports VCC down to 1 V operation. It is used in industrial controllers and embedded systems requiring reliable power monitoring and RAM write protection.

For engineers reviewing the ADM691AARNZ-REEL datasheet, ADM691AARNZ-REEL pinout, ADM691AARNZ-REEL application, or ADM691AARNZ-REEL equivalent, key selection criteria include reset voltage accuracy (±3%), battery switchover hysteresis (60 mV), VCC-to-VOUT on-resistance (0.8–1.2 Ω), standby current (70–100 µA), and compatibility with 5 V ±5% supplies.

Technical Context

The ADM691AARNZ-REEL implements a dual-voltage comparator architecture for VCC monitoring and battery switchover, with independent thresholds for power-up (VBATT + 0.03 V) and power-down (VBATT – 0.03 V). Its internal oscillator supports fixed (200 ms / 1.6 s) or capacitor-adjustable timing via OSC IN/OSC SEL pins.

It integrates a three-level WDI input with transition-based watchdog restart logic, open-drain RESET and complementary active-high RESET outputs, and CMOS RAM write protection via CEIN/CEOUT gating with 6 ns propagation delay and 40–150 Ω on-resistance.

Key Specifications

Pinout & Package

ADM691AARNZ-REEL is housed in a 16-pin narrow SOIC (R-16N) package with 1.27 mm pitch, RoHS-compliant, tape-and-reel format (REEL suffix).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX691ACPP+, ADM691AARNZ-REEL offers superior timing flexibility and lower standby current; compared with TPS3823MPW, it delivers full supervisory functionality including battery switchover and RAM write protection - making it the only complete solution for systems requiring all five core functions.

Availability

ADM691AARNZ-REEL is available at Aetrix Electronics and suitable for industrial PLC controllers, medical diagnostic instruments, automotive body control modules, and telecom remote terminal units requiring stable component supply and long-term lifecycle support.

Supply support for ADM691AARNZ-REEL 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, founded in 1965 and headquartered in Wilmington, MA.

The ADM691A series belongs to Analog Devices' microprocessor supervisory product line, designed specifically for robust power monitoring, battery backup, and system-level fault recovery in mission-critical embedded systems.

FAQ

What is the reset voltage threshold accuracy of the ADM691AARNZ-REEL?

The ADM691AARNZ-REEL has a guaranteed reset voltage threshold of 4.65 V with ±3% tolerance over temperature and supply variations. This specification ensures reliable reset assertion for 5 V ±5% power rails while avoiding false triggers due to noise or ripple. The threshold is laser-trimmed at wafer test and validated across –40°C to +85°C. ADM691AARNZ-REEL maintains this accuracy without external components.

Can the ADM691AARNZ-REEL support both internal and external timing sources for reset and watchdog functions?

Yes, the ADM691AARNZ-REEL supports multiple timing configurations via OSC SEL and OSC IN pins. With OSC SEL floating, internal oscillator modes provide fixed 200 ms reset and 1.6 s watchdog timeouts. Pulling OSC SEL low enables external timing: an RC network on OSC IN sets both periods proportionally (e.g., 47 pF → 200 ms / 1.6 s), or an external clock (≤250 kHz) defines them as 2048/fCLK and 1024/fCLK cycles. ADM691AARNZ-REEL's datasheet Table II documents all combinations.

How does the ADM691AARNZ-REEL handle battery backup switchover during VCC brownout?

The ADM691AARNZ-REEL uses a dual-threshold comparator to switch VOUT from VCC to VBATT when VCC drops below (VBATT – 0.03 V), with 60 mV hysteresis to prevent chatter. In battery mode, VOUT is sourced through a 7 Ω MOSFET, delivering up to 10 mA with <150 mV dropout at 5 mA. Battery standby current is 0.04–1 µA, enabling multi-year operation on CR2032 cells. ADM691AARNZ-REEL also asserts BATT ON high to drive external PNP transistors for higher current loads.

What is the function of the CEIN and CEOUT pins on the ADM691AARNZ-REEL?

CEIN and CEOUT implement hardware-enforced RAM write protection. CEOUT is a buffered replica of CEIN when VCC is valid (>4.65 V), with 6 ns propagation delay. When VCC falls below the reset threshold, CEOUT is forced high independently of CEIN, disabling chip select/write signals to battery-backed CMOS RAM. This prevents data corruption during power-up, brownout, or shutdown. ADM691AARNZ-REEL's CEOUT can sink/source ±100 µA and operates down to VCC = 1 V.

Does the ADM691AARNZ-REEL provide power-fail warning capability, and how is it implemented?

Yes, the ADM691AARNZ-REEL includes a dedicated power-fail comparator with a precise 1.25 V internal reference. The PFI pin accepts a divided-down version of the main supply (e.g., 7 V → 1.25 V via R1/R2), and PFO asserts low within 25–60 µs when PFI drops below 1.25 V. This provides early warning before VCC reaches the 4.65 V reset threshold, allowing µP to save critical data. ADM691AARNZ-REEL supports hysteresis addition via external R3 between PFO and PFI for noise immunity.