Union Semiconductor UM803RS

The UM803 is a microprocessor (μP) supervisory circuit used to monitor the power supplies in μP and digital systems. It provides excellent circuit reliability and low cost by eliminating external components and adjustments when used with +5V, +3.3V, +3.0V or +2.5V powered circuits. The circuit performs a single function: it asserts a reset signal whenever the VCC supply voltage declines below a preset threshold, keeping it asserted for at least 140ms after VCC has risen above the reset threshold. Reset thresholds suitable for operation with a variety of supply voltages are available. The UM803 has an open-drain output stage. The UM803’s open-drain RESET output requires a pull-up resistor that can be connected to a voltage higher than VCC. The UM803 has an active-low RESET output. The reset comparator is designed to ignore fast transients on VCC, and the outputs are guaranteed to be in the correct logic state for VCC down to 1V. A microprocessor’s (μP's) reset input starts the μP in a known state. The UM803 asserts reset to prevent code-execution errors during power-up, power-down, or brownout conditions. It asserts a reset signal whenever the VCC supply voltage declines below a preset threshold, keeping it asserted for at least 140ms after VCC has risen above the reset threshold. The UM803 uses an open-drain output. Connect a pull-up resistor on the UM803’s RESET output to any supply between 0 and 6V.

• No External Components
• Power Supply Transient Immunity
• Guaranteed Reset Valid to VCC = +1V
• Precision VCC Monitoring of +2.5V, +3V, +3.3V and +5V Supplies
• Fully Specified Over Temperature
• 2μA Supply Current
• 140ms Minimum Power-On Reset Pulse Width
• Available in One Output Configuration: Open-Drain Active-Low RESET Output
• 3-Pin SOT323 and SOT23 Packages
• Wide Operation Temperature: -40°C to +85°C

• Computers
• Controllers
• Portable/Battery-Powered Equipments
• Intelligent Instruments
• Critical μP and μC Power Monitoring
• Automotive