Analog Devices Inc./Maxim Integrated MAX791CSE+T

Overview

MAX791CSE+T from Maxim Integrated is a microprocessor supervisory circuit providing precision 4.65V reset monitoring, 200ms reset timeout, dual-stage power-fail warning (PFI/PFO + LOWLINE), battery switchover (25mA backup mode), and adjustable watchdog timer - all in a 16-pin narrow SO package. It ensures reliable µP reset during power-up/down/brownout and supports CMOS RAM backup in portable and industrial systems.

For engineers reviewing the MAX791CSE+T datasheet, MAX791CSE+T pinout, MAX791CSE+T application, or MAX791CSE+T equivalent, this page delivers verified functional scope, validated pin roles, confirmed timing behavior (6ns CE propagation, 1.6s default watchdog), and real-world substitution guidance for µP power-monitoring designs.

Technical Context

The MAX791CSE+T integrates a precision 4.65V reset comparator with 15mV hysteresis, a separate 4.80V low-line comparator (150mV above reset threshold), and an independent 1.25V power-fail comparator (PFI/PFO). Its battery switchover logic activates when VCC falls below both the reset threshold and VBATT, enabling seamless VOUT sourcing from VBATT with <25mA continuous output capability.

Watchdog functionality uses an internal current source charging the SWT capacitor to set timeout (2.1 × C_nF ms); WDI accepts TTL/CMOS-level transitions and disables automatically if floating. Chip-enable gating enforces 6ns CE propagation delay and forces CE OUT high during reset to prevent memory corruption.

Key Specifications

Pinout & Package

MAX791CSE+T is housed in a 16-pin narrow SO (Small Outline) package, 3.9mm width, RoHS-compliant lead-free variant (indicated by "+T" suffix).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX691ACPE+ and TPS3823MPW, the MAX791CSE+T uniquely combines 4.65V precision reset, adjustable watchdog, LOWLINE/NMI support, and integrated battery switchover in a narrow SO package - making it irreplaceable for legacy +5V µP systems requiring full-featured supervision without layout change.

Availability

MAX791CSE+T is available at Aetrix Electronics and suitable for industrial PLC control, portable medical monitoring, embedded network routing, and automotive infotainment head units requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for MAX791CSE+T 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, computing, and communications markets.

The MAX791 product line was designed specifically for comprehensive +5V microprocessor supervision - integrating reset, watchdog, power-fail warning, battery backup, and memory protection in a single 16-pin IC to reduce system complexity and improve reliability.

FAQ

What is the guaranteed minimum VCC level at which MAX791CSE+T maintains valid RESET output?

The MAX791CSE+T guarantees valid RESET output down to VCC = 1V when no backup battery is connected. With VBATT ≥2V present, RESET remains valid across the full VCC range (0V to 5.5V). This behavior is confirmed in the Electrical Characteristics table under "RESET Output Voltage" and "RESET, LOW-LINE, AND WATCHDOG TIMER" sections, where ISINK = 50µA tests at VCC = 1.0V (MAX791C) and VCC = 1.2V (MAX791E/M) verify correct logic levels.

How does the MAX791CSE+T implement battery switchover, and what are the voltage conditions required?

The MAX791CSE+T switches VOUT to VBATT when two conditions are met simultaneously: VCC falls below the reset threshold (4.65V typ) AND VCC falls below VBATT. This is explicitly defined in the "Battery-Backup Mode" section and Table 1. The switchover threshold has 60mV hysteresis, and VOUT in battery mode maintains VBATT – 0.15V at 5mA load - ensuring stable backup power for CMOS RAM or RTC without external circuitry.

Can the watchdog timeout of MAX791CSE+T be disabled, and how is this accomplished?

Yes, the watchdog function of MAX791CSE+T is disabled by leaving the WDI pin unconnected. An internal 100kΩ resistor network biases WDI to ~1.6V, which the internal comparators recognize as an invalid state, disabling the watchdog timer. This is documented in the "Watchdog Input" section and Note 4 of the Electrical Characteristics - no pull-up/down resistors or additional components are needed.

What is the purpose of the LOWLINE output on MAX791CSE+T, and how does it differ from RESET?

The LOWLINE output on MAX791CSE+T is an active-low signal triggered when VCC falls to ~4.80V (150mV above the 4.65V reset threshold), providing early warning before RESET assertion. Unlike RESET, LOWLINE has no hysteresis control over the µP - it's intended for nonmaskable interrupt (NMI) generation to initiate graceful shutdown, data save, or audio mute, giving the system ~10–50ms of advance notice before hard reset occurs.

Does MAX791CSE+T support write-protection of CMOS RAM, and how is it implemented?

Yes, MAX791CSE+T implements CMOS RAM write protection via its chip-enable (CE) gating function. When RESET is asserted, CE OUT is forced high regardless of CE IN state, blocking memory writes. During normal operation, CE IN passes through to CE OUT with 6ns propagation delay. This is detailed in the "Chip-Enable Signal Gating" section and Figure 1 block diagram - no external logic is required to prevent corruption during power faults.