Analog Devices Inc./Maxim Integrated MAX690RESA+

Overview

MAX690RESA+ from Maxim Integrated is a 3.0V/3.3V microprocessor supervisory circuit with active-low RESET output, 2.625V reset threshold (R-suffix), 200ms reset timeout, watchdog timer (1.6s), and battery-backup switchover. It monitors VCC supply integrity, asserts reset during brownout or watchdog timeout, and switches CMOS RAM to VBATT when VCC falls below 2.40V - used in embedded controllers and portable equipment requiring reliable power sequencing.

For engineers reviewing the MAX690RESA+ datasheet, MAX690RESA+ pinout, MAX690RESA+ application, or MAX690RESA+ equivalent, key selection criteria include guaranteed RESET assertion down to VCC = 1V, ±4% reset threshold accuracy, 40µA VCC supply current, and compatibility with lithium backup batteries exceeding VCC voltage.

Technical Context

The MAX690RESA+ integrates a precision reset comparator with 10mV hysteresis, a non-disableable 1.6s watchdog timer cleared by WDI edges, and a dual-path power switch: VCC-to-VOUT via 3Ω PMOS and VBATT-to-VOUT via 140Ω NMOS. Reset assertion is guaranteed for VCC < 2.625V (falling) and remains active for 200ms after recovery.

Its battery switchover logic triggers at VSW = 2.40V (VBATT > VCC), defers reconnection to VCC until VCC rises above the reset threshold (not VSW), and disables PFI comparator and watchdog during battery-backup mode - ensuring deterministic low-power retention for static RAM.

Key Specifications

Pinout & Package

MAX690RESA+ is housed in an 8-pin SOIC package (SO) with lead-free finish (+ suffix), 1.27mm pitch, and standard JEDEC MS-012 outline.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX706RESA+, MAX690RESA+ adds essential watchdog supervision and battery switchover; compared with MAX805RESA+, it provides direct active-low drive without external pull-up, simplifying layout and reducing component count.

Availability

MAX690RESA+ is available at Aetrix Electronics and suitable for battery-powered embedded controllers, critical µP power monitoring, and intelligent portable instruments requiring stable component supply across industrial temperature ranges (-40°C to +85°C).

Supply support for MAX690RESA+ 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

Maxim Integrated (now part of Analog Devices) designs high-performance analog and mixed-signal ICs for power, sensing, and connectivity applications.

The MAX690 family targets 3.0V/3.3V microprocessor systems needing integrated reset, watchdog, and battery-backup management - optimized for reliability in portable, medical, and industrial equipment.

FAQ

What is the exact reset threshold voltage for MAX690RESA+?

The MAX690RESA+ has a nominal reset threshold of 2.625V with ±4% tolerance on the falling edge (2.55V to 2.70V). This value is specified for VCC falling conditions and ensures reset assertion before VCC drops below 2.55V in 3.0V systems. The rising-edge threshold is slightly higher (2.55V to 2.72V) due to 10mV hysteresis, preventing oscillation near the trip point. This specification is confirmed in the Electrical Characteristics table of the MAX690 datasheet.

Does MAX690RESA+ support battery voltages higher than VCC?

Yes, MAX690RESA+ explicitly supports VBATT exceeding VCC - a key design feature enabling direct connection of 3.6V lithium batteries to the VBATT pin while VCC operates at 3.0V or 3.3V. The internal battery switchover circuit activates when VCC falls below 2.40V (VSW), connecting VBATT to VOUT through a 140Ω switch. This eliminates the need for external diodes or regulators, preserving efficiency and board space in compact portable designs using MAX690RESA+.

Can the watchdog timer in MAX690RESA+ be disabled?

No, the watchdog timer in MAX690RESA+ cannot be disabled. It is a fixed-function block that triggers a reset if the WDI pin remains static (high or low) for longer than 1.6 seconds. The timer clears only on rising or falling edges at WDI or during active RESET assertion. This design ensures continuous supervision of µP activity without software dependency - a safety-critical feature confirmed in the Detailed Description section of the MAX690 datasheet.

What is the maximum allowable VCC transient duration that will not trigger a reset in MAX690RESA+?

For a 100mV overdrive (i.e., VCC falling 100mV below the 2.625V reset threshold), MAX690RESA+ tolerates negative-going transients up to 40µs without issuing a reset pulse, as shown in Figure 7 of the datasheet. This immunity is achieved through internal filtering and comparator hysteresis. Adding a 100nF bypass capacitor close to the VCC pin further enhances robustness against short-duration supply glitches, making MAX690RESA+ suitable for electrically noisy environments.

How does MAX690RESA+ handle power-fail detection when no external supply is monitored?

When the power-fail function is unused, MAX690RESA+ requires PFI to be connected to GND and PFO left unconnected (open-drain). This configuration disables the power-fail comparator and prevents floating input errors. The datasheet explicitly states this practice in the Pin Description and Applications Information sections. Leaving PFI unconnected risks noise-induced false PFO assertions, so grounding PFI is mandatory for reliable MAX690RESA+ operation in systems without auxiliary supply monitoring.