Analog Devices Inc./Maxim Integrated MAX690AESA+T

Overview

The MAX690AESA+T from Maxim Integrated is a microprocessor supervisory circuit providing precision reset generation, battery-backup switchover, watchdog timer, and power-fail detection for +5V systems. It asserts an active-low RESET pulse (200ms width) when VCC drops below 4.65V, switches VOUT to VBATT during brownout, monitors PFI against a 1.25V reference, and triggers reset if WDI is un-toggled for 1.6s-used in battery-powered controllers and critical μP power monitoring.

For engineers reviewing the MAX690AESA+T datasheet, MAX690AESA+T pinout, MAX690AESA+T application, or MAX690AESA+T equivalent, key selection criteria include guaranteed RESET assertion down to VCC = 1V, 50nA quiescent current in battery-backup mode, ±2% power-fail accuracy (shared with MAX802L), 8-pin SO package compatibility, and pin equivalence with MAX690/MAX694.

Technical Context

The MAX690AESA+T integrates four independent functional blocks: a precision voltage monitor with 4.65V threshold and 40mV hysteresis, a 1.6s watchdog timer cleared by WDI edges or RESET assertion, a battery switchover circuit using dual PMOS switches (5Ω for VCC→VOUT, 80Ω for VBATT→VOUT), and a 1.25V reference-based power-fail comparator driving open-drain PFO.

Its reset generator guarantees logic-low output at VCC ≥ 1V and maintains 200ms pulse width after VCC rises above threshold; the backup mode activates only when VCC falls below 4.65V *and* VBATT exceeds VCC by >20mV, with 40mV hysteresis preventing chatter during slow droop.

Key Specifications

Pinout & Package

MAX690AESA+T is housed in an 8-pin SOIC (Small Outline Integrated Circuit) package, 3.9mm × 4.9mm body, 1.27mm pitch, RoHS-compliant lead-free construction.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX802LESA+, the MAX690AESA+T offers identical supervision functionality but is optimized for cost-sensitive industrial designs where ±2% PFI accuracy is not contractually mandated; versus MAX706TESA+, it adds essential battery backup and early-warning capability at minimal footprint cost.

Availability

MAX690AESA+T is available at Aetrix Electronics and suitable for battery-powered computers and controllers, intelligent instruments, critical μP power monitoring, industrial PLCs, and portable data acquisition systems requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for MAX690AESA+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) designs precision analog and mixed-signal ICs for industrial, communications, and computing applications, emphasizing reliability, integration, and low-power operation.

The MAX690AESA+T belongs to Maxim's μP supervisory circuit product line, engineered specifically to replace discrete reset generators, voltage monitors, and battery switchover circuits in space-constrained embedded systems operating from +5V rails.

FAQ

What is the guaranteed minimum VCC level at which MAX690AESA+T asserts RESET?

The MAX690AESA+T guarantees RESET assertion down to VCC = 1V. This ensures fail-safe behavior during deep brownout conditions where the supply rail collapses gradually. The device maintains logic-low RESET output until VCC recovers above 4.65V and sustains the 200ms pulse width. This specification is verified across the full -40°C to +85°C operating temperature range and is critical for systems relying on capacitor hold-up or supercapacitor backup.

Does MAX690AESA+T support active-high reset outputs?

No, the MAX690AESA+T provides only an active-low RESET output. Its pin 7 is labeled RESET (not RESET). For active-high reset functionality, the MAX805L variant is required - it provides an inverted RESET output that goes high during reset assertion. The MAX690AESA+T's RESET pin is open-drain compatible and requires an external pull-up resistor to VCC or VOUT depending on system-level voltage domain requirements.

How does the battery switchover logic work in MAX690AESA+T?

The MAX690AESA+T activates battery switchover only when two conditions are simultaneously met: VCC falls below the 4.65V reset threshold *and* VBATT exceeds VCC by more than 20mV. At that point, the internal 80Ω PMOS switch connects VBATT to VOUT. When VCC rises above VBATT + 20mV, the 5Ω PMOS reconnects VCC to VOUT. This hysteresis prevents oscillation during slow VCC recovery and limits battery discharge to true brownout events - unlike earlier MAX690 versions, it does not connect VBATT to VOUT whenever VBATT > VCC.

What is the maximum allowable backup battery voltage for MAX690AESA+T?

The maximum allowable backup battery voltage for MAX690AESA+T is 4.80V, as specified in Maxim's Table 2. Exceeding this voltage risks forward-biasing the internal substrate diode (D1 in Figure 3) when VCC approaches the reset threshold, causing unintended current flow from VBATT into the die. Lithium cells with 3.0V–3.6V open-circuit voltage are ideal; higher-voltage sources require series diodes or regulators to comply with the 4.80V absolute limit.

Can MAX690AESA+T monitor negative supply rails?

Yes, the MAX690AESA+T's PFI input can monitor negative 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 comparator triggers PFO low when the magnitude of the negative voltage decreases (i.e., becomes less negative). Accuracy depends on PFI input current (±25nA max), resistor tolerance, and VCC stability - typical use cases include monitoring -5V or -12V analog supply integrity in mixed-signal instrumentation.