FM811SUX

Supervisors Overview

The FM811SUX is a microprocessor supervisory circuit manufactured by Fairchild Semiconductor, housed in a 4-pin SOT-143 surface-mount package. It provides precise voltage monitoring for power supplies operating at 3V, 3.3V, or 5V. The device features an active low RESET output that asserts when the supply voltage drops below a designated threshold or the manual reset pin is forced low. It guarantees a minimum reset pulse width of 140ms after VCC rises above the threshold and remains valid with VCC as low as 1.4V. The circuit draws a typical supply current of 6µA and requires no external components.

Supervisors Feature Summary

• Precision voltage monitoring for 3V, 3.3V, and 5V systems
• Active low manual reset input capability
• Guaranteed 140ms minimum reset pulse width
• Reset validity maintained down to 1.4V supply voltage

Supervisors Applications

• Critical microprocessor power monitoring
• Portable equipment power management
• Intelligent instruments supervision
• Computers and printers control systems
• Industrial controllers

Supervisors Procurement Notes

Verify the specific voltage threshold variant (3V, 3.3V, or 5V) required for your application, as the base part number may denote different thresholds. Confirm the SOT-143 package compatibility with your PCB footprint. Ensure the active low reset logic aligns with your microprocessor's reset input requirements. Check for RoHS compliance status if environmental regulations apply to your manufacturing process.

Supervisors Selection Notes

Select this component when a low-cost, single-channel supervisor is needed for standard logic voltage levels. The 6µA supply current makes it suitable for battery-powered applications where standby power consumption is critical. The absence of external components simplifies design and reduces bill of materials cost. Consider the 140ms timeout duration to ensure it meets the startup time requirements of the target system.

Supervisors Part Context

The FM811 series belongs to Fairchild's family of microprocessor reset circuits, designed to replace discrete resistor-capacitor networks. It integrates precision comparators and timing circuits into a compact SOT-143 package. The sibling part FM812 offers an active high reset output, providing flexibility for different logic families. These devices are engineered for reliability in industrial and consumer electronics environments.

Supervisors Replacement Considerations

The MAX811REUS+T from Analog Devices/Maxim Integrated is a functional equivalent offering similar supervisor capabilities in a SOT-143-4 package. Verify that the reset threshold voltages and pulse widths match your system specifications before substitution.