Microprocessor Supervisory Circuits

The MAX690 family of supervisory circuits reduces the complexity and number of components required for power supply monitoring and battery control functions in microprocessor systems. These include µP reset and backup-battery switchover, watchdog timer, CMOS RAM write protection, and power-failure warning. The MAX690 family significantly improves system reliability and accu- racy compared to that obtainable with separate ICs or discrete components.

The MAX690, MAX692, and MAX694 are supplied in 8-pin packages and provide four functions:

* A reset output during power-up, power-down, and brownout conditions.

* Battery backup switching for CMOS RAM, CMOS microprocessor or other low power logic.

* A Reset pulse if the optional watchdog timer has not been toggled within a specified time.

* A 1.3V threshold detector for power fail warning, low battery detection, or to monitor a power supply other than +5V.

The MAX691, MAX693, and MAX695 are supplied in 16-pin packages and perform all MAX690, MAX692, MAX694 functions, plus:

* Write protection of CMOS RAM or EEPROM.

* Adjustable reset and watchdog timeout periods.

* Separate outputs for indicating a watchdog timeout, backup-battery switchover, and low VCC. Applications

* Automotive Systems * Computers * Controllers * Critical µP Power Monitoring * Intelligent Instruments

* Supervisory Function Integration Saves Board Space while Fully Protecting Microprocessor-Based Systems

* Precision Voltage Monitor

* 4.65V (MAX690, MAX691, MAX694, MAX695)

* 4.40V (MAX692, MAX693)

* Power OK/Reset Time Delay

* 50ms, 200ms, or Adjustable

* Watchdog Timer

* 100ms, 1.6s, or Adjustable

* Battery Backup Power Switching

* Voltage Monitor for Power Fail or Low Battery Warning

* Minimum External Component Count

* Low Power Consumption in Battery Backup Mode Extends Battery Life

* 1µA Standby Current

* Onboard Gating of Chip Enable Signals Protects Against Erroneous Data Written to RAM During Low VCC Events