1 Features
1• 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 VCC ≥ 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, powerdown
and brown-out conditions.
The function of the LM809 and LM810 are to monitor
the VCC supply voltage, and assert a reset signal
whenever this voltage declines below the factoryprogrammed
reset threshold. The reset signal
remains asserted for 240 ms after VCC 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.