Analog Devices Inc./Maxim Integrated MAX694CPA

Overview

The MAX694CPA from Maxim Integrated is an 8-pin microprocessor supervisory circuit providing reset generation, battery backup switchover, watchdog timer, and 1.3V power-fail detection for +5V systems. It delivers a 4.65V reset threshold, 200ms reset timeout, fixed 1.6s watchdog timeout, and VOUT switching between VCC and VBATT - used in industrial controllers and embedded instrumentation to ensure reliable µP startup, brownout recovery, and RAM data retention during power loss.

For engineers reviewing the MAX694CPA datasheet, MAX694CPA pinout, MAX694CPA application, or MAX694CPA equivalent, key selection considerations include its 200ms reset delay (vs. 50ms in MAX690), 4.65V reset threshold tolerance, battery switchover hysteresis (50mV/70mV), PFI comparator accuracy (±0.1V), and compatibility with 2.0–4.25V backup batteries - all critical for deterministic reset timing and fail-safe memory backup in safety-critical µP systems.

Technical Context

The MAX694CPA integrates four core supervisory functions in a single 8-pin DIP package: a precision voltage monitor with 4.65V ±150mV reset threshold and 40mV hysteresis; a monostable reset generator producing a guaranteed 140–280ms active-low pulse after VCC recovery; a fixed 1.6s watchdog timer triggered by WDI transitions; and a 1.3V reference-based power-fail comparator (PFI/PFO) with ±0.1V threshold tolerance and <25nA input current.

Its internal battery switchover circuit uses a low-dropout PNP switch and 200Ω MOSFET to route VOUT to the higher of VCC or VBATT, with 50mV power-down and 70mV power-up switchover thresholds and 20mV hysteresis - enabling seamless CMOS RAM backup without external transistors while maintaining ≤1µA standby current when VCC = 0V and VBATT = 2.8V.

Key Specifications

Pinout & Package

MAX694CPA is supplied in an 8-pin plastic DIP (dual in-line package) with 0.3-inch body width and standard through-hole mounting. Pin 1 is marked with a notch or dot; pins are numbered counterclockwise from top-left.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX690CPA, MAX694CPA provides 4× longer reset timeout for robust oscillator stabilization; versus TPS3823-50DBVR, it adds full supervisory integration (switchover, watchdog, PFI) at the cost of larger DIP footprint - making MAX694CPA the sole choice for legacy industrial systems requiring all four functions in one 8-pin device.

Availability

MAX694CPA is available at Aetrix Electronics and suitable for industrial controllers, embedded instrumentation, automotive body electronics, and critical µP power monitoring applications requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for MAX694CPA 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 communications markets.

The MAX690 family - including MAX694CPA - was designed specifically for microprocessor-based systems requiring integrated power supervision, battery backup, and fail-safe reset timing in space-constrained industrial and instrumentation applications.

FAQ

What is the reset timeout delay of the MAX694CPA, and how does it differ from the MAX690CPA?

The MAX694CPA features a guaranteed 200ms reset timeout delay (min 140ms, max 280ms) after VCC rises above its 4.65V threshold. This is four times longer than the MAX690CPA's 50ms delay. The extended duration ensures reliable microprocessor initialization, especially for systems using crystal oscillators requiring >100ms startup time. Both parts share identical reset threshold accuracy and watchdog timing, but the MAX694CPA's longer reset pulse prevents premature µP execution during marginal power recovery events.

Does the MAX694CPA support battery backup switchover, and what are the voltage requirements?

Yes, the MAX694CPA supports automatic battery backup switchover via its VBATT and VOUT pins. It accepts backup batteries from 2.0V to 4.25V and switches VOUT to VBATT when VCC falls below VBATT minus 50mV (power-down) or 70mV (power-up), with 20mV hysteresis to prevent oscillation. During switchover, VOUT delivers VBATT – 0.1V at 250µA load, and the device draws only 0.6–1.0µA from the battery when VCC = 0V - enabling multi-year retention for CMOS RAM and RTC circuits.

Can the watchdog timer on the MAX694CPA be disabled, and how is it configured?

Yes, the watchdog timer on the MAX694CPA is disabled by leaving the WDI pin floating or driving it to mid-supply (~38% of VCC). When enabled, it requires a transition on WDI every 1.6s (nominal) to prevent a 200ms RESET pulse. Unlike the 16-pin MAX695, the MAX694CPA has no adjustable watchdog period - its timeout is fixed internally. The WDI pin has built-in biasing (125kΩ to 38% VCC), so no external pullup/down is needed for disable operation.

What is the function of the PFI and PFO pins on the MAX694CPA, and how accurate is the power-fail detection?

The PFI pin is the noninverting input of a comparator referenced to an internal 1.3V bandgap, and PFO is its active-low open-drain output. When PFI voltage falls below 1.3V ±0.1V, PFO asserts to signal impending power failure. This allows early warning (e.g., 10–20ms before reset) by connecting PFI to a resistor divider on the main 5V rail or unregulated input. The ±0.1V tolerance ensures consistent triggering across temperature and supply variations, supporting reliable data-save routines in µP systems.

Is the MAX694CPA pin-compatible with other devices in the MAX690 family, and what are the key package details?

Yes, the MAX694CPA is pin-compatible with MAX690CPA and MAX692CPA in the 8-pin plastic DIP package (0.3-inch width, 0.1-inch pin spacing). All share identical pinout: VBATT (1), RESET (2), WDI (3), PFO (4), VOUT (5), VCC (6), PFI (7), GND (8). The 'C' suffix denotes commercial temperature range (0°C to +70°C), and 'PA' specifies plastic DIP packaging. No PCB layout changes are required when substituting within this 8-pin group, though functional differences (e.g., reset delay, threshold voltage) must be verified in system firmware.