1 Features

• Precision Monitoring of Supply Voltages
  • Available Threshold Options:
    2.63 V, 2.93 V, 3.08 V, 4.38 V, 4.63 V
• Superior Upgrade to MAX809 and MAX810
• Fully Specified Over Temperature
• 140-ms Minimum Power-On Reset Pulse Width, 240-ms Typical
  • Active-Low RESET Output (LM809)
  • Active-High RESET Output (LM810)
• Ensured RESET Output Valid for V_CC ≥ 1 V
• Low Supply Current, 15-µA Typical
• Power Supply Transient Immunity

2 Applications

• Factory Automation
• Building Automation
• Programmable Logic Control
• Renewable Energy
• Microprocessor Systems
• Computers
• Controllers
• Intelligent Instruments
• Portable/Battery-Powered Equipment
• Automotive

3 Description

The LM809 and LM810 microprocessors supervisory circuits can be used to monitor the power supplies in microprocessor and digital systems. They provide a reset to the microprocessor during power-up, power-down and brown-out conditions.

The function of the LM809 and LM810 are to monitor the V_CC supply voltage, and assert a reset signal whenever this voltage declines below the factory-programmed reset threshold. The reset signal remains asserted for 240 ms after V_CC rises above the threshold. The LM809 has an active-low RESET output, while the LM810 has an active-high RESET output.

Seven standard reset voltage options are available, suitable for monitoring 5-V, 3.3-V, and 3-V supply voltages.

With a low supply current of only 15 µA, the LM809 and LM810 are ideal for use in portable equipment.

1. For all available packages, see the orderable addendum at the end of the data sheet.

Typical Application for Microprocessor Reset Circuit