Microprocessor Supervisory Circuits

The MAX696/MAX697 supervisory circuits reduce the complexity and number of components required for power-supply monitoring and battery-control functions in microprocessor (µP) systems. These include µP reset and backup-battery switchover, watchdog timer, CMOS RAM write protection, and power-failure warning. The MAX696/MAX697 significantly improve system reliability and accuracy compared to that obtained with separate ICs or discrete components.

The MAX696 and MAX697 are supplied in 16-pin packages and perform six functions:

* A reset output during power-up, power-down, and brownout conditions. The threshold for this "lowline" reset is adjustable by an external voltage-divider.

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

* Individual outputs for low-line and watchdog fault conditions.

* The reset time may be left at its default value of 50ms, or may be varied with an external capacitor or clock pulses.

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

The MAX696 also has battery-backup switching for CMOS RAM, CMOS microprocessor, or other low-power logic.

The MAX697 lacks battery-backup switching, but has write-protection pins (active-low CE IN and active-low CE OUT) for CMOS RAM or EPROM. In addition, it consumes less than 250 microamperes.

Applications

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

* Adjustable Low-Line Monitor and Power-Down Reset

* Power-OK/Reset Time Delay

* Watchdog Timer—100ms, 1.6s, or Adjustable

* Minimum Component Count

* 1µA Standby Current

* Battery-Backup Power Switching (MAX696)

* On-Board Gating of Chip-Enable Signals (MAX697)

* Separate Monitor for Power-Fail or Low-Battery Warning