Microprocessor Supervisory Circuit MAX791

General Description

The MAX791 microprocessor (µP) supervisory circuit reduces the complexity and number of components needed to monitor power-supply and battery-control functions in µP systems. The 50µA supply current makes the MAX791 ideal for use in portable equipment, while the 6ns chip-enable propagation delay and 250mA output capability (25mA in battery-backup mode) make it suitable for larger, higher-performance equipment.

The MAX791 comes in 16-pin DIP and narrow SO packages and provides the following functions:

1) µP reset—– RESET output is asserted during power-up, power-down, and brownout conditions,

and is guaranteed to be in the correct state for V_CC down to 1V, even with no battery in the circuit.

2) Manual-reset input.

3) A 1.25V threshold detector provides for power-fail warning and low-battery detection, or monitors a power

supply other than +5V.

4) Two-stage power-fail warning—a separate low-line comparator compares V_CC to a threshold 150mV above

the reset threshold.

5) Backup-battery switchover for CMOS RAM, real-time clocks, µPs, or other low-power logic.

6) Software monitoring of backup-battery voltage.

7) A watchdog-fault output is asserted if the watchdog input has not been toggled within either a preset or an

adjustable timeout period.

8) Write protection of CMOS RAM or EEPROM.

9) Pulsed watchdog output, to give advance warning of impending WDO assertion caused by

watchdog timeout.

Applications

Computers Critical µP Power Monitoring

Controllers Intelligent Instruments

Portable/Battery-Powered Equipment

Pin Configuration

Features

♦ Precision 4.65V Voltage Monitoring

♦ 200ms Power-OK/Reset Time Delay

♦ Independent Watchdog Timer—Preset or Adjustable

♦ 1µA Standby Current

♦ Power Switching 250mA Output in V_CC Mode 25mA Output in Battery-Backup Mode

♦ On-Board Gating of Chip-Enable Signals Memory Write-Cycle Completion 6ns CE Gate Propagation Delay

♦ MaxCap^TM or SuperCap^TM Compatible

♦ Voltage Monitor for Power-Fail or Low-Battery Warning

♦ Backup-Battery Monitor

♦ Guaranteed RESET Valid to V_CC = 1V

Ordering Information

* Dice are specified at TA = +25°C.

Typical Operating Circuit

ABSOLUTE MAXIMUM RATINGS

Input Voltage (with respect to GND)

V_CC.......................................................................-0.3V to +6V

VBATT..................................................................-0.3V to + 6V

All Other Inputs.....................................-0.3V to (V_OUT + 0.3V)

Input Current

V_CC Peak ..........................................................................1.0A

V_CC Continuous ............................................................250mA

VBATT Peak ..................................................................250mA

VBATT Continuous..........................................................25mA

GND, BATT ON.............................................................100mA

All Other Outputs ............................................................25mA

Continuous Power Dissipation (TA = +70°C)

Plastic DIP (derate 10.53mW/°C above +70°C) ..........842mW

Narrow SO (derate 8.70mW/°C above +70°C) ............696mW

CERDIP (derate 10.00mW/°C above +70°C)...............800mW

Operating Temperature Ranges

MAX791C_ _ ......................................................O°C to +70°C

MAX791E_ _ ....................................................-40°C to +85°C

MAX791MJE ..................................................-55°C to +125°C

Storage Temperature Range .............................-65°C to +160°C

Lead Temperature (soldering, 10sec) .............................+300°C

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

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