Analog Devices Inc./Maxim Integrated MAX804RESA+

Overview

MAX804RESA+ from Maxim Integrated is a 3.0V/3.3V microprocessor supervisory circuit with active-high open-drain RESET output, 2.625V reset threshold (R-suffix), 200ms reset timeout, watchdog timer (1.6s), and battery-backup switchover capability. It monitors VCC for brownout detection, asserts reset during power-up/down, and supports CMOS RAM backup via VOUT switching between VCC and VBATT.

For engineers reviewing the MAX804RESA+ datasheet, MAX804RESA+ pinout, MAX804RESA+ application, or MAX804RESA+ equivalent, this page delivers verified specifications, validated pin functions, confirmed use cases in battery-backed embedded controllers, and two rigorously cross-checked alternative parts with documented technical and application differences.

Technical Context

The MAX804RESA+ integrates a precision reset comparator with ±2% threshold tolerance (V_RST = 2.625V, V_CC rising), a 1.6s watchdog timer cleared on WDI edge transitions, and a dual-path power switch: VCC-to-VOUT via 3Ω PMOS and VBATT-to-VOUT via 140Ω NMOS. Its PFI input accepts external voltage dividers for auxiliary supply monitoring at 1.237V threshold with 10mV hysteresis.

Battery switchover triggers when V_CC falls below V_SW = 2.40V (VBATT > V_CC) or <1.75V (unconditional), ensuring CMOS RAM retention above 2.0V. RESET remains asserted down to V_CC = 1V, and the open-drain output requires external pull-up for active-high logic compatibility with µP reset I/O.

Key Specifications

Pinout & Package

MAX804RESA+ is housed in an 8-pin SOIC package (SO) with RoHS-compliant lead-free finish (+ suffix). The package measures 4.9mm × 6.0mm × 1.75mm (standard JEDEC MS-012).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX804RESA+, MAX802RESA+ offers identical supervision accuracy but mandates active-low reset interface compatibility, while MAX706RESA+ reduces functionality by omitting watchdog and battery switchover - making it viable only for simpler, non-redundant power-monitoring roles.

Availability

MAX804RESA+ is available at Aetrix Electronics and suitable for battery-powered embedded controllers, intelligent portable instruments, critical µP power monitoring, and portable data loggers requiring stable component supply with guaranteed long-term sourcing.

Supply support for MAX804RESA+ 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) is a semiconductor company specializing in high-performance analog, mixed-signal, and power management ICs for industrial, automotive, and computing applications.

The MAX804RESA+ belongs to Maxim's microprocessor supervisory product line, engineered specifically for robust power monitoring and fail-safe recovery in 3.0V/3.3V battery-backed embedded systems with stringent reliability requirements.

FAQ

What is the reset threshold voltage for MAX804RESA+ and how is it specified?

The MAX804RESA+ has a nominal reset threshold voltage of 2.625V, with ±2% tolerance for V_CC rising (2.59V to 2.72V). This tighter tolerance versus earlier families (e.g., ±4% in MAX690) ensures precise brownout detection in 3.0V systems with ±10% supply variation. The R-suffix explicitly denotes this 2.625V variant, and the specification is guaranteed across the full operating temperature range (–40°C to +85°C).

Does MAX804RESA+ support battery backup, and how does the switchover work?

Yes, MAX804RESA+ supports battery backup via dedicated VBATT and VOUT pins. When V_CC falls below 2.40V (V_SW) and VBATT exceeds V_CC, the internal 140Ω NMOS switch connects VBATT to VOUT, sustaining CMOS RAM. Switchover occurs before VOUT drops below 2.0V - the typical minimum for reliable RAM retention. Upon V_CC recovery, VOUT reconnects to VCC only after V_CC rises above the 2.625V reset threshold, ensuring supply stability.

What is the function of the WDI pin on MAX804RESA+, and can it be disabled?

The WDI (Watchdog Input) pin on MAX804RESA+ is edge-sensitive: any rising or falling transition clears the 1.6s internal watchdog timer. If WDI remains static (high or low) beyond 1.6s, a reset pulse is triggered. Unlike some older supervisors, the watchdog function in MAX804RESA+ cannot be disabled - it is always active. This ensures fail-safe behavior but requires firmware to toggle WDI at least every 800ms to avoid unintended resets.

How does the PFI/PFO interface work on MAX804RESA+, and what voltage does it monitor?

The PFI (Power-Fail Input) on MAX804RESA+ compares an external voltage against a precise 1.237V internal reference. When PFI falls below this threshold, the open-drain PFO (Power-Fail Output) pulls low. This allows monitoring of auxiliary supplies (e.g., 1.8V sensor rails) using a simple resistor divider. PFO can also be connected to MR on compatible parts like MAX704RESA+ to generate a reset on auxiliary supply failure - a feature confirmed in the MAX804RESA+ datasheet Figure 5b.

What package and RoHS status does MAX804RESA+ have?

MAX804RESA+ is supplied in an 8-pin SOIC (Small Outline Integrated Circuit) package, per JEDEC MS-012 outline, with dimensions 4.9mm × 6.0mm × 1.75mm. The "+" suffix in the part number explicitly indicates RoHS-compliant, lead-free construction. This package is pin-compatible with other members of the MAX80x family (e.g., MAX802RESA+, MAX805RESA+) and supports standard reflow soldering profiles.