Analog Devices Inc./Maxim Integrated MAX690ACSA+T

Overview

The MAX690ACSA+T from Maxim Integrated is a microprocessor supervisory circuit providing power-on reset, brownout detection, watchdog timer, battery-backup switchover, and power-fail warning in a single 8-pin SO package. It asserts a 200ms active-low RESET pulse when VCC drops below 4.65V, supports 1.6s watchdog timeout, delivers up to 50mA from VOUT, and draws only 200µA quiescent current during normal operation. It is used in battery-powered controllers and intelligent instruments requiring reliable μP initialization and backup power management.

For engineers reviewing the MAX690ACSA+T datasheet, MAX690ACSA+T pinout, MAX690ACSA+T application, or MAX690ACSA+T equivalent, key selection criteria include its 4.65V reset threshold, guaranteed RESET assertion down to VCC = 1V, 50nA battery-backup mode current, PFI comparator with 1.25V internal reference, and compatibility with CMOS RAM and 80C51-family microprocessors.

Technical Context

The MAX690ACSA+T integrates a precision voltage monitor, a monostable reset generator with 200ms delay, a 1.6s watchdog timer cleared by WDI edges or reset assertion, and a dual-path power switch (5Ω PMOS for VCC→VOUT, 80Ω PMOS for VBATT→VOUT). Its reset logic guarantees low output until VCC rises above 4.65V and remains low for exactly 200ms thereafter.

The device features an independent 1.25V power-fail comparator (PFI/PFO), battery switchover hysteresis of 40mV, and operates across VCC = 1.0V to 5.5V. In backup mode (VCC < 4.65V and VBATT > VCC + 20mV), it powers VOUT from VBATT while drawing <1µA from the battery when VCC is >1V below VBATT.

Key Specifications

Pinout & Package

MAX690ACSA+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 finish (indicated by '+' suffix).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX692ACSA+T, the MAX690ACSA+T offers higher reset threshold for tighter +5V regulation margin; compared with MAX802LCSA+T, it lacks guaranteed ±2% PFI accuracy but maintains identical reset behavior and lower unit cost.

Availability

MAX690ACSA+T is available at Aetrix Electronics and suitable for battery-powered controllers, intelligent instruments, and critical μP power monitoring requiring stable component supply, long-lifecycle support, and RoHS-compliant packaging.

Supply support for MAX690ACSA+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, with emphasis on reliability and integration.

The MAX690A family targets microprocessor supervisory functions-combining reset generation, watchdog, battery switchover, and power-fail detection in minimal footprint for space-constrained embedded systems.

FAQ

What is the guaranteed minimum VCC level at which MAX690ACSA+T asserts RESET?

The MAX690ACSA+T guarantees RESET remains asserted (low) down to VCC = 1.0V. This ensures the microprocessor stays held in reset even during deep brownout conditions or slow power ramp-down, preventing erratic execution. The specification is tested and guaranteed across the full operating temperature range, making MAX690ACSA+T suitable for applications demanding robust low-voltage reset behavior.

Does MAX690ACSA+T support active-high reset output?

No, MAX690ACSA+T provides only active-low RESET output. The active-high variant is the MAX805L series (e.g., MAX805LCSA+T), which outputs RESET instead of RESET. MAX690ACSA+T's RESET pin is open-drain and requires an external pull-up resistor; its logic state is low during reset assertion and high-impedance otherwise. For Intel 80C51 or other μPs requiring active-high reset, MAX805LCSA+T is the direct functional alternative.

How does the watchdog timer in MAX690ACSA+T get cleared?

The watchdog timer in MAX690ACSA+T is cleared by any rising or falling edge on the WDI pin, by assertion of the RESET output, or by three-stating WDI (high-impedance). It is not cleared by holding WDI high or low continuously - doing so triggers a reset after 1.6s. The timer resumes counting immediately after RESET deasserts or WDI transitions from high-impedance to driven state, ensuring continuous supervision of firmware liveness.

Can MAX690ACSA+T monitor a negative supply rail?

Yes, MAX690ACSA+T can monitor a negative rail using the PFI input with 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 degradation (less negative voltage) and pulls PFO low. Accuracy depends on resistor tolerance and PFI input bias current (≤25nA), but the circuit is validated in the datasheet for applications like monitoring –5V or –12V supplies.

What is the maximum allowable VBATT voltage for MAX690ACSA+T?

The maximum allowable VBATT voltage for MAX690ACSA+T is 4.80V, as specified in Table 2 of the datasheet. Exceeding this risks forward-biasing the internal substrate diode (D1 in Figure 3) when VCC is near the reset threshold, causing unintended current flow from VBATT into the die. Lithium cells (3.0–3.6V) and properly sized supercapacitors are recommended; for higher-voltage sources, external regulation or clamping is required before connection to VBATT.