Analog Devices Inc./Maxim Integrated MAX805LESA

Overview

The MAX805LESA from Maxim Integrated is a microprocessor supervisory circuit providing active-high reset, battery-backup switchover, watchdog timer, and power-fail detection for +5V systems. It asserts RESET at 4.65V threshold with 200ms pulse width, supports 1.6s watchdog timeout, draws 200µA supply current, and operates from –40°C to +85°C in 8-pin SO package-used in industrial controllers requiring reliable brownout recovery and RAM backup.

For engineers reviewing the MAX805LESA datasheet, MAX805LESA pinout, MAX805LESA application, or MAX805LESA equivalent, key selection criteria include its active-high RESET output (vs. active-low alternatives), guaranteed reset assertion down to VCC = 1.1V, ±2% power-fail accuracy, battery-switching hysteresis of 40mV, and compatibility with Intel 80C51-style µPs requiring high-true reset signaling.

Technical Context

The MAX805LESA integrates four independent functional blocks: a precision voltage monitor with 4.65V reset threshold and 40mV hysteresis; a 1.6s watchdog timer cleared by WDI edge transitions; a 1.25V reference-based power-fail comparator driving PFO; and a dual-path battery switchover circuit that connects VOUT to VBATT only when VCC falls below 4.65V and VBATT exceeds VCC by ≥20mV.

Its internal architecture uses a P-channel MOSFET for VCC-to-VOUT connection (5Ω on-resistance) and an 80Ω PMOS switch for VBATT-to-VOUT backup mode, with quiescent current dropping to 50nA in battery-backup operation. The RESET output is actively driven high during assertion (not open-drain), enabling direct interface to µPs like the 80C51 without external pull-ups.

Key Specifications

Pinout & Package

MAX805LESA is housed in an 8-pin SOIC (Small Outline Integrated Circuit) package with standard 1.27mm pitch, JEDEC MS-012AC compliant, and RoHS-compliant lead-free finish (indicated by "+" suffix).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX802LESA, the MAX805LESA eliminates external level-shifting components for 80C51-based designs; compared with MAX813LESA, it offers cost-optimized tolerance for industrial applications where ±3% threshold variation is acceptable per IEC 61000-4-11 immunity testing.

Availability

MAX805LESA is available at Aetrix Electronics and suitable for industrial PLCs, medical infusion pumps, smart energy meters, ruggedized handheld testers, and battery-backed data loggers requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for MAX805LESA 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, communications, and computing markets.

The MAX805L product line was designed specifically for microprocessor-based systems needing integrated reset, watchdog, battery switchover, and power-fail warning functions in a single 8-pin package-targeting cost-sensitive yet reliability-critical embedded applications.

FAQ

What is the reset output polarity of the MAX805LESA?

MAX805LESA features an active-high RESET output, meaning it drives high during reset assertion and low otherwise. This distinguishes it from the MAX802L series, which provides active-low RESET. The MAX805LESA's push-pull output is directly compatible with µPs such as the Intel 80C51 that require a high-true reset signal, eliminating the need for external inverters or pull-up resistors in those designs.

Does the MAX805LESA support battery backup for CMOS RAM?

Yes, MAX805LESA supports battery backup for CMOS RAM through its VOUT pin and VBATT input. When VCC drops below the 4.65V reset threshold and VBATT exceeds VCC by at least 20mV, the internal 80Ω PMOS switch connects VBATT to VOUT. In this mode, MAX805LESA draws only 50nA from the battery, enabling multi-year retention of RAM contents on a single lithium coin cell-critical for applications like smart meters and medical devices.

What is the minimum VCC voltage at which MAX805LESA guarantees RESET assertion?

MAX805LESA guarantees valid RESET assertion down to VCC = 1.1V, as confirmed in the Electrical Characteristics table under "RESET Output Voltage" test condition. This ensures deterministic reset behavior during deep brownout events where the +5V rail collapses below 2V, allowing µPs to enter safe states before complete power loss-a key requirement for fail-safe industrial control systems.

How does the watchdog timer in MAX805LESA operate?

The MAX805LESA watchdog timer triggers a reset if the WDI pin remains static (high or low) for longer than 1.6 seconds. The timer clears on any rising or falling edge at WDI, on RESET assertion, or when WDI is left floating (high-impedance). Unlike some competitors, MAX805LESA's watchdog does not require periodic toggling-it only requires edge activity within the timeout window, simplifying firmware implementation while still preventing software lockup.

Can MAX805LESA monitor power supplies other than +5V?

Yes, MAX805LESA can monitor non-+5V supplies using its PFI input and internal 1.25V reference. By connecting a resistor divider from the target supply to PFI, users scale the monitored voltage so that the divider output equals 1.25V at the desired trip point-for example, detecting failure of a +3.3V rail at 3.0V or a –12V rail using the negative-monitoring circuit in Figure 7 of the datasheet. PFO then provides an active-low flag for µP interrupt handling.