Analog Devices Inc. ADM691ARZ

Overview

ADM691ARZ 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 automatic VCC/VBATT switching to VOUT with ≤0.75 Ω on-resistance. It is used in industrial controllers and embedded systems requiring reliable power monitoring and RAM write protection.

For engineers reviewing the ADM691ARZ datasheet, ADM691ARZ pinout, ADM691ARZ application, or ADM691ARZ equivalent, key selection criteria include reset voltage accuracy, battery switchover hysteresis (60 mV), CEOUT propagation delay (≤10 ns), WDI transition sensitivity, and compatibility with 5 V ±5% supplies.

Technical Context

The ADM691ARZ implements a dual-threshold voltage detector (4.65 V nominal with 15 mV hysteresis) and an internal oscillator that sets both reset delay and watchdog timeout-configurable via OSC SEL/OSC IN for fixed (200 ms / 1.6 s) or adjustable timing using external capacitor or clock. Its battery switchover uses PMOS (VCC→VOUT) and NMOS (VBATT→VOUT) switches with validated dropout behavior down to VBATT = 2.0 V.

Chip enable gating provides active-high CEOUT synchronized to CEIN during valid VCC, forced high during reset or brownout; the LOW LINE output asserts immediately on VCC drop below threshold, while PFI/PFO operate independently with 1.25 V reference and 25 µs response. All digital outputs (RESET, WDO, PFO, BATT ON) are open-drain or push-pull with specified sink/source drive capability.

Key Specifications

Pinout & Package

ADM691ARZ is packaged in a 16-pin narrow-body SOIC (R-16N), RoHS-compliant, with standard 1.27 mm pitch and 10.2 mm × 7.5 mm footprint.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX691ACPE+, ADM691ARZ delivers tighter reset accuracy, lower quiescent current, and integrated PFI/PFO-reducing BOM count by two comparators and associated resistors. Versus TPS3823MPW, ADM691ARZ adds essential battery management and system-level supervision missing in basic reset ICs.

Availability

ADM691ARZ 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 across extended temperature ranges and long production lifecycles.

Supply support for ADM691ARZ 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 ADM691A family was designed specifically for microprocessor-based systems needing integrated power monitoring, battery backup, and watchdog safety-targeting reliability-critical embedded applications where discrete supervision solutions increase complexity and failure risk.

FAQ

What is the guaranteed reset threshold voltage for ADM691ARZ?

The ADM691ARZ has a guaranteed reset threshold of 4.5 V minimum and 4.75 V maximum at +25°C, with a typical value of 4.65 V ±3%. This specification ensures reliable reset assertion for +5 V systems operating within ±5% tolerance, and the 15 mV hysteresis prevents chatter during slow VCC recovery. The ADM691ARZ maintains functional reset generation down to VCC = 1 V, supporting brownout hold-down in low-voltage conditions.

How does ADM691ARZ handle battery switchover during power failure?

The ADM691ARZ automatically switches VOUT from VCC to VBATT when VCC drops below VBATT – 0.03 V during power-down, with 60 mV hysteresis to prevent oscillation. In battery backup mode, VOUT is sourced from VBATT via a 7 Ω switch, delivering up to 5 mA at 2.0 V with <0.15 V dropout. The ADM691ARZ draws only 0.04 µA typical supply current in this state, enabling multi-year coin-cell operation. BATT ON asserts high to drive external PNP transistors for loads exceeding 250 mA.

Can ADM691ARZ generate adjustable watchdog timeout periods?

Yes, ADM691ARZ supports adjustable watchdog timeout via OSC SEL and OSC IN pins. With OSC SEL grounded, connecting a capacitor (C) from OSC IN to GND yields a timeout of 600 × (C/47 pF) ms. Using an external clock (fCLK) at OSC IN gives Twd = 1024 / fCLK. These methods allow precise tuning from ~100 ms to several seconds-critical for matching software execution cycles without over-constraining firmware timing margins. The ADM691ARZ also offers fixed 100 ms and 1.6 s modes for simplified implementation.

What is the function of the dual RESET pins on ADM691ARZ?

The ADM691ARZ provides two complementary reset outputs: pin 15 (RESET) is active-low open-drain, and pin 16 (RESET) is active-high push-pull. This eliminates the need for external inverters when interfacing with processors requiring opposite reset polarity. Both outputs are asserted simultaneously during power-up, brownout, or watchdog timeout. The ADM691ARZ guarantees RESET remains low down to VCC = 1 V, ensuring robust shutdown sequencing even during deep undervoltage events.

Does ADM691ARZ support power-fail warning for rails other than +5 V?

Yes, ADM691ARZ supports power-fail warning for any rail via its PFI input, which compares against a precision 1.25 V internal reference. By configuring an external resistor divider from the target rail (e.g., 3.3 V, 12 V, or unregulated input) to PFI, designers can set custom trip points-for example, triggering PFO at 7 V on a 12 V input to provide >100 ms warning before 5 V regulator dropout. The ADM691ARZ maintains PFI/PFO functionality in battery backup mode as long as VCC ≥ VBATT – 1.2 V.