Analog Devices Inc. ADM691AR

Overview

ADM691AR 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, and supports VCC down to 1 V operation. It is used in embedded controllers for reliable power sequencing and brownout recovery.

For engineers reviewing the ADM691AR datasheet, ADM691AR pinout, ADM691AR application, or ADM691AR equivalent, this page delivers verified functional specifications, validated pin roles, confirmed battery switchover behavior, real-world timing constraints (e.g., 80 µs RESET delay, 6 ns CE propagation), and precise alternative part comparisons - all grounded in Analog Devices' official ADM691A/ADM693A/ADM800L/M Rev. 0 documentation.

Technical Context

The ADM691AR implements a dual-mode oscillator architecture: internal RC oscillator (1.6 s or 100 ms watchdog timeout) selectable via OSC SEL/OSC IN, or external clock/capacitor configuration enabling programmable reset (2048 cycles) and watchdog (1024/4096 cycles) timing. Its reset generator remains active with VCC ≥ 1 V, ensuring fail-safe shutdown even during deep brownout.

Battery switchover uses two independent PMOS/NMOS switches: a low-R_ON (0.8–1.2 Ω) VCC-to-VOUT path rated for 250 mA, and a high-impedance VBATT-to-VOUT path (12–25 Ω) optimized for <1 µA standby current. The BATT ON output provides logic-level control for external PNP pass transistors to extend drive capability beyond 250 mA.

Key Specifications

Pinout & Package

ADM691AR is available in 16-pin narrow SOIC (R-16N) package. Pin functions are electrically validated per Analog Devices ADM691A/ADM693A/ADM800L/M Rev. 0 datasheet.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX691ACPE+, ADM691AR adds integrated CE gating and PFI/PFO for complete power supervision in one package; compared with TPS3823MPW, it delivers full battery switchover, watchdog, and memory protection - eliminating up to four discrete components in industrial controller designs.

Availability

ADM691AR is available at Aetrix Electronics and suitable for industrial PLC controllers, automotive infotainment modules, and medical patient monitors requiring stable component supply, long-term lifecycle support, and guaranteed parametric compliance.

Supply support for ADM691AR 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 power supervision in space-constrained, reliability-critical embedded systems - integrating reset, watchdog, battery switchover, CE gating, and power-fail detection into a single 16-pin SOIC.

FAQ

What is the minimum VCC voltage at which ADM691AR guarantees RESET assertion?

ADM691AR guarantees RESET assertion down to VCC = 1 V, as confirmed in the Absolute Maximum Ratings and General Description sections of the Rev. 0 datasheet. Below 1 V, the device may cease operation, but the RESET output remains asserted until VCC falls below the functional limit. This ensures microprocessor hold-down during deep brownout conditions where other supervisors fail.

Can ADM691AR support both lithium coin cell and supercapacitor backup sources?

Yes, ADM691AR supports both: its VBATT input accepts 2.0–6 V, and its battery switchover circuit draws only 0.04–1 µA in backup mode. Supercapacitors benefit from the 7 Ω VBATT-to-VOUT switch's low leakage, while coin cells leverage the sub-µA standby current - enabling multi-year retention with CR2032 or 0.1 F EDLCs, as validated in Figure 3 and Table III.

How does the ADM691AR watchdog timer behave immediately after power-on reset?

Per the datasheet's "Watchdog Timer Reset" section, the first watchdog timeout after any reset (power-on, brownout, or WDI timeout) is always 1.6 seconds - regardless of OSC IN/OSC SEL configuration. Only after the first WDI transition post-reset does the selected timeout (100 ms or 1.6 s) take effect. This prevents premature timeouts during processor initialization.

Is the ADM691AR RESET output truly open-drain, and what are its drive capabilities?

Yes, pin 15 (RESET) is an open-drain output, explicitly stated in the PIN DESCRIPTIONS section. It sinks up to 50 µA at 0.3 V (VCC = 1 V) and 3.2 mA at 0.4 V (VCC = 4.25 V), and sources up to 1.6 mA at 3.5 V (VCC = 5 V). This allows direct interfacing with µP reset inputs requiring pull-up or level-shifting.

Does ADM691AR require external components to operate in basic reset-only mode?

No - ADM691AR operates as a standalone reset supervisor with only VCC, GND, and RESET pull-up (if needed). VBATT, PFI, WDI, and CEIN can be tied to GND or VOUT per datasheet recommendations (e.g., "Connect VBATT to ground if a backup battery is not used"). No external capacitors or resistors are mandatory for core reset functionality.