Analog Devices Inc./Maxim Integrated MAX704TEPA+

Overview

MAX704TEPA+ from Maxim Integrated is a 3.3V microprocessor supervisory circuit with active-low RESET output, precision 3.075V reset threshold (±4%), 200ms reset timeout, watchdog timer (1.6s), and battery-backup switchover. It monitors VCC supply integrity, asserts reset during power-up/brownout/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 MAX704TEPA+ datasheet, MAX704TEPA+ pinout, MAX704TEPA+ application, or MAX704TEPA+ equivalent, key selection criteria include guaranteed RESET assertion down to VCC = 1V, 40µA VCC supply current, ±75mV power-fail comparator accuracy, and compatibility with lithium backup batteries exceeding VCC voltage.

Technical Context

The MAX704TEPA+ integrates a precision reset comparator with 10mV hysteresis, a non-disableable 1.6s watchdog timer cleared by WDI edges, and a dual-path battery switchover circuit using PMOS switches (3Ω VCC-to-VOUT, 140Ω VBATT-to-VOUT). Its PFI input accepts external voltage dividers for multi-rail monitoring, while PFO provides open-drain power-fail warning.

RESET is asserted low whenever VCC < 3.075V, MR is low, or watchdog times out - with 200ms minimum pulse width and guaranteed deassertion only after VCC exceeds 3.085V and timer expires. Battery switchover occurs at VSW = 2.40V (VBATT > VCC), and reconnection to VCC is deferred until VCC rises above the reset threshold to ensure stability.

Key Specifications

Pinout & Package

MAX704TEPA+ is housed in an 8-pin plastic DIP (PDIP) package with 0.300" wide body and through-hole mounting. Pin spacing is 0.100", lead finish is lead-free (RoHS-compliant), and thermal resistance is 9.09mW/°C above +70°C.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX704TEPA+, MAX706TEPA+ adds active-high reset but removes watchdog capability, while MAX803TEPA+ reduces feature set to minimize footprint and cost - both retain identical reset timing and threshold accuracy for direct substitution in non-watchdog or non-MR use cases.

Availability

MAX704TEPA+ is available at Aetrix Electronics and suitable for battery-powered computers and controllers, intelligent instruments, and critical µP power monitoring requiring stable component supply across industrial temperature ranges.

Supply support for MAX704TEPA+ 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 industrial, communications, and computing applications.

The MAX704 series belongs to Maxim's microprocessor supervisory product line, engineered specifically for reliable power monitoring and reset generation in 3.0V/3.3V embedded systems with battery backup requirements.

FAQ

What is the reset threshold voltage of the MAX704TEPA+ and how tightly is it specified?

The MAX704TEPA+ has a nominal reset threshold voltage of 3.075V for VCC falling, with a tolerance of ±4% (3.00V to 3.15V). This specification ensures robust brownout detection in 3.3V systems with ±5% supply tolerance, and the device guarantees RESET assertion before VCC falls below 3.00V. The MAX704TEPA+ also exhibits 10mV typical hysteresis to prevent chatter near the trip point.

Does the MAX704TEPA+ support battery voltages higher than the main VCC supply?

Yes, the MAX704TEPA+ explicitly supports VBATT exceeding VCC - a core design feature enabling direct connection of standard 3.6V lithium coin cells. Switchover to battery occurs when VCC falls below 2.40V (VSW) while VBATT > VCC, and the internal 140Ω switch ensures low-loss backup power delivery to VOUT. This eliminates external diodes and associated voltage drop.

Can the watchdog timer in the MAX704TEPA+ be disabled?

No, the watchdog timer in the MAX704TEPA+ cannot be disabled. It is a hardwired, non-maskable function that triggers a RESET pulse if the WDI input remains static (high or low) for longer than 1.6 seconds. The timer clears only on rising or falling edges at WDI - making it ideal for fail-safe firmware supervision in safety-critical applications.

What is the purpose of the PFI and PFO pins on the MAX704TEPA+?

The PFI (Power-Fail Input) and PFO (Power-Fail Output) pins on the MAX704TEPA+ form an independent voltage-monitoring channel. PFI compares an external voltage (e.g., from a resistor divider) against a 1.237V internal reference; when that voltage falls below threshold, PFO goes low. This allows monitoring of auxiliary supplies like 5V sensor rails or analog subsystems - and PFO can be connected to MR to generate a reset on secondary rail failure.

How does the MAX704TEPA+ behave during VCC transients or short glitches?

The MAX704TEPA+ is designed to ignore short-duration negative-going VCC transients: a 100mV dip below the reset threshold lasting ≤40µs will not trigger RESET. This immunity is achieved via internal filtering and comparator overdrive tolerance, preventing spurious resets during switching noise or ESD events. A 0.1µF bypass capacitor at VCC further enhances transient rejection.