Analog Devices Inc./Maxim Integrated MAX690ACPA

Overview

The MAX690ACPA from Maxim Integrated is a microprocessor supervisory circuit in 8-pin plastic DIP packaging, providing precision 4.65V reset threshold detection, 200ms reset pulse width, 1.6s watchdog timeout, battery-backup switchover, and 1.25V power-fail comparator functionality for +5V μP systems. It ensures reliable power-up, brownout, and power-down reset assertion while enabling CMOS RAM retention during main supply failure.

For engineers reviewing the MAX690ACPA datasheet, MAX690ACPA pinout, MAX690ACPA application, or MAX690ACPA equivalent, this device serves as a critical system-level reliability component in battery-backed embedded controllers, intelligent instrumentation, and industrial μP monitoring where deterministic reset timing, low-quiescent-current backup operation, and accurate voltage supervision are required.

Technical Context

The MAX690ACPA integrates four independent supervisory functions: a precision bandgap-referenced reset generator with hysteresis, a monostable watchdog timer cleared by WDI edges or reset assertion, a dedicated 1.25V comparator for PFI-based power-fail warning, and a dual-path PMOS battery switchover circuit with 40mV hysteresis between VCC and VBATT.

Its internal architecture separates reset generation (triggered by VCC < 4.65V, watchdog timeout, or manual assertion) from power-fail signaling (PFO low when PFI < 1.25V), allowing independent use of each function. The VOUT output switches between VCC (5Ω on-resistance) and VBATT (80Ω on-resistance) based solely on VCC threshold crossing and relative voltage conditions - no external control logic required.

Key Specifications

Pinout & Package

MAX690ACPA is housed in an 8-pin plastic DIP (dual in-line package) with 0.3-inch body width and through-hole mounting. Pin spacing is 0.1 inch, compatible with standard PCB layouts and socketing.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX802LCPA, MAX690ACPA offers equivalent supervision performance with broader legacy design adoption; versus MAX705CPA, it adds critical battery management and predictive power-fail signaling at minimal incremental cost and zero PCB layout change.

Availability

MAX690ACPA 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 and long-term production continuity.

Supply support for MAX690ACPA 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 is a semiconductor company specializing in analog and mixed-signal ICs for power management, interface, sensing, and reliability-critical applications.

The MAX690A series belongs to Maxim's microprocessor supervisory product line, designed specifically to replace discrete reset generators, voltage monitors, and battery switchover circuits in embedded systems requiring high-accuracy, low-power, and fault-tolerant power management.

FAQ

What is the guaranteed minimum operating voltage for MAX690ACPA reset assertion?

The MAX690ACPA guarantees RESET output assertion down to VCC = 1.0V, ensuring reliable hold-reset behavior even during severe brownout conditions where supply voltage collapses below typical logic thresholds. This specification is verified across the full 0°C to +70°C operating temperature range and is critical for maintaining μP in known state during deep undervoltage events. The MAX690ACPA achieves this using a dedicated low-voltage detection circuit independent of the main bandgap reference.

Does MAX690ACPA support active-high reset output?

No, the MAX690ACPA provides only active-low RESET output. The active-high variant is the MAX805L family (e.g., MAX805LCPA), which substitutes RESET for RESET and guarantees valid output down to VCC = 1.1V. MAX690ACPA's RESET pin is open-drain compatible and intended for direct connection to μP reset inputs requiring active-low assertion, such as Intel 80Cxx or Motorola 68xxx families. Using MAX690ACPA with active-high reset μPs requires external inversion.

What is the maximum allowable backup battery voltage for MAX690ACPA?

The maximum allowable backup battery voltage for MAX690ACPA is 4.80V, as specified in Maxim's application documentation. Exceeding this voltage risks forward-biasing the internal substrate diode (D1) when VCC approaches the 4.65V reset threshold, causing unintended current flow from VBATT into the die substrate and potential latch-up or accelerated aging. Lithium cells with nominal 3.0–3.6V open-circuit voltage are ideal; higher-voltage sources require series regulation or clamping.

How does the MAX690ACPA watchdog timer interact with the reset signal?

The MAX690ACPA watchdog timer resets its 1.6s counter whenever RESET is asserted, WDI is three-stated, or a rising/falling edge is detected on WDI. While RESET is active, the timer remains cleared and does not count. Upon RESET release, the timer resumes counting and must be serviced within 1.6s to prevent another reset pulse. This tight coupling ensures that software hangs are recovered without requiring separate reset sequencing logic - the MAX690ACPA handles both supervision and recovery autonomously.

Can MAX690ACPA monitor negative supply rails?

Yes, the MAX690ACPA's PFI input can monitor negative voltage rails using an external resistor network as shown in Maxim's Figure 7. By referencing PFI to ground and applying the negative rail through a voltage divider, the internal 1.25V comparator detects when the magnitude of the negative supply decreases (i.e., becomes less negative), causing PFO to go high. Accuracy depends on resistor tolerance and PFI input bias current (≤25nA), so 1% metal-film resistors are recommended. This technique enables undervoltage detection on -5V, -12V, or -15V supplies without additional ICs.