FM809JS3X

Supervisors Overview

The FM809JS3X is a precision voltage supervisory circuit manufactured by onsemi, originally part of the Fairchild Semiconductor portfolio. It operates within a supply voltage range of 1.1 V to 5.5 V and features a fixed under-voltage threshold of 3.9 V with an over-voltage threshold of 4.18 V. The device provides a 560 ms reset delay and delivers an active low, push-pull output. Designed for surface-mount installation in a SOT-23-3 package, it consumes only 10 uA of operating current. The component supports an industrial temperature range from -40°C to +105°C and lacks manual reset or watchdog timer functions.

Supervisors Feature Summary

• Provides precise monitoring of single power supply rails with defined under-voltage and over-voltage thresholds.
• Delivers a deterministic reset signal via an active low, push-pull output interface.
• Maintains ultra-low quiescent current consumption suitable for battery-powered applications.
• Ensures reliable operation across extended industrial temperature ranges.

Supervisors Applications

• Microprocessor system reset circuits
• Portable electronic device power management
• Industrial control board supervision

Supervisors Procurement Notes

Verify component authenticity due to discontinued status and potential legacy stock availability. Confirm manufacturer origin as onsemi/Fairchild Semiconductor matches design requirements. Validate RoHS compliance documentation against specific revision codes. Ensure SOT-23-3 footprint compatibility during procurement planning. Check for obsolescence notices affecting long-term supply continuity.

Supervisors Selection Notes

Select this component when a fixed 3.9 V under-voltage threshold is required without adjustable options. Consider the 560 ms delay duration against system startup timing constraints. Evaluate the 10 uA current draw against strict power budget limitations. Verify that the active low output polarity aligns with downstream logic inputs. Confirm SOT-23-3 package suitability for available PCB real estate.

Supervisors Part Context

The FM809 series belongs to a family of 3-pin UC supervisor circuits designed for voltage monitoring. Originally developed by Fairchild Semiconductor, production rights transferred to onsemi. This specific variant integrates fixed threshold detection without external resistor networks. It serves as a dedicated power management IC within the broader PMIC category.

Supervisors Replacement Considerations

FM809RS3X is documented as a related variant within the same functional family. Verify pinout and threshold specifications before substitution. No other public substitute part numbers are confirmed for direct replacement.