Analog Devices Inc./Maxim Integrated MAX818LCUA+

Overview

MAX818LCUA+ from Maxim Integrated is a +5V microprocessor supervisory circuit with active-low reset, battery backup switchover, watchdog timer (1.6s timeout), and on-board chip-enable gating. It features a 4.65V ±5% reset threshold, 200ms reset timeout, and 11µA quiescent supply current-designed for undervoltage monitoring and RAM protection in portable embedded systems.

For engineers reviewing the MAX818LCUA+ datasheet, MAX818LCUA+ pinout, MAX818LCUA+ application, or MAX818LCUA+ equivalent, this device delivers integrated power-fail immunity, battery-freshness seal control, and sub-15ns CE propagation delay-critical for reliable µP boot sequencing and brownout recovery in space-constrained battery-powered equipment.

Technical Context

The MAX818LCUA+ implements a precision bandgap-based reset comparator with 25mV hysteresis and internal 200ms monostable timer to guarantee reset assertion during VCC transitions. Its dual-path power switch (5Ω VCC-to-OUT, 80Ω BATT-to-OUT) enables seamless switchover when VCC drops below both VRST (4.65V) and VBATT.

It integrates a dedicated transmission gate for chip-enable signal gating (CE IN → CE OUT), with 40Ω on-resistance and 15µs disable delay during reset assertion-ensuring CMOS RAM write completion before isolation. The watchdog input (WDI) accepts 50ns pulses and clears on edge transitions or internal servicing every ~1.4s when floating.

Key Specifications

Pinout & Package

MAX818LCUA+ is housed in an 8-pin µMAX package (3mm × 3mm, 0.5mm pitch), optimized for PCB area-constrained portable designs. Pin functions are validated per Maxim's official datasheet revision 3 (12/05).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX818LCUA+, MAX817LCSA+ trades CE gating for power-fail detection, while MAX819LESA+ adds MR but removes watchdog functionality-making MAX818LCUA+ the sole option combining all three: CE protection, watchdog supervision, and battery switchover in µMAX.

Availability

MAX818LCUA+ is available at Aetrix Electronics and suitable for portable medical monitors, industrial data loggers, smart metering modules, and handheld test equipment requiring stable component supply across extended production lifecycles.

Supply support for MAX818LCUA+ 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 precision analog and mixed-signal ICs for power management, sensing, and interface applications in industrial, automotive, and computing markets.

The MAX817/MAX818/MAX819 product line targets +5V µP systems needing integrated reset, battery backup, and signal gating-reducing discrete component count while ensuring robust power-supply monitoring.

FAQ

What is the reset threshold voltage of the MAX818LCUA+?

The MAX818LCUA+ has a factory-trimmed reset threshold of 4.65V ±5%, optimized for +5V systems with ±5% supply tolerance. This value is specified over the full operating temperature range (0°C to +70°C) and exhibits only ±10mV drift from 0°C to +70°C per the typical characteristics graph (Figure MAX817/18/19-10). The threshold is internally generated using a precision bandgap reference, ensuring stability without external components.

Does the MAX818LCUA+ support battery backup switchover, and what are the conditions?

Yes, the MAX818LCUA+ supports automatic battery backup switchover. Switchover occurs only when two conditions are met simultaneously: VCC falls below the reset threshold (4.65V) AND VCC falls below VBATT. Once engaged, OUT connects to BATT through an 80Ω internal PMOS switch, drawing less than 1µA when VCC < VBATT − 0.2V. The device remains in backup mode until VCC rises above both VRST and VBATT.

How does the chip-enable gating function work on the MAX818LCUA+?

The MAX818LCUA+ uses an internal transmission gate between CE IN (pin 5) and CE OUT (pin ?) to isolate RAM during reset. When RESET is asserted, the gate disables within 15µs-holding CE OUT low to complete any ongoing write cycle. During normal operation, CE IN passes directly to CE OUT with 3ns propagation delay and 40Ω series resistance. This design prevents corrupted writes during brownout without requiring external logic.

Is the watchdog timer on the MAX818LCUA+ enabled by default, and how is it serviced?

The watchdog timer on the MAX818LCUA+ is enabled by default and times out after 1.6 seconds. It is serviced by any rising or falling edge on WDI (pin 6); pulses as short as 50ns are recognized. If WDI is left unconnected, the internal watchdog circuitry automatically services the timer every ~1.4 seconds via an internal low-high-low pulse-eliminating the need for external circuitry unless deterministic reset timing is required.

Can the MAX818LCUA+ be used with a supercapacitor as a backup source?

Yes, the MAX818LCUA+ is compatible with supercapacitors as backup sources. Its BATT input accepts 2.0V–6.0V, and the switchover comparator operates with ±30mV hysteresis centered at VBATT. When paired with a simple charging circuit (e.g., diode + resistor), a 0.47F supercap can provide minutes of backup runtime. Decoupling with a 0.1µF capacitor at BATT is mandatory per the Applications Information section to ensure stable switching.