FAN2509S285X

Voltage Regulators - Linear, Low Drop Out (LDO) Regulators Overview

The FAN2509S285X is a fixed-output micropower low-dropout (LDO) linear voltage regulator from the FAN2508/09 family, manufactured by onsemi. It provides a nominal output voltage of 2.85V with a maximum continuous output current of 50mA. The device utilizes CMOS technology and features an Enable pin for shutdown control and an ERR pin that functions as an open-drain error flag to indicate when the output voltage drops below 95% of its nominal value due to faults such as input dropout or thermal overload. It operates within an input voltage range of 2.7V to 6.5V and supports junction temperatures up to 125°C.

Voltage Regulators - Linear, Low Drop Out (LDO) Regulators Feature Summary

• Integrated ERR pin serves as an open-drain diagnostic flag indicating output voltage degradation below specified thresholds.
• CMOS-based design enables ultra-low power consumption and extremely low quiescent ground current during operation.
• Includes onboard thermal limiting protection that automatically disables the output if die temperature exceeds safe operating limits.
• Supports flexible loop stability across a wide range of external capacitor ESR values without requiring specific component types.

Voltage Regulators - Linear, Low Drop Out (LDO) Regulators Applications

• GSM and TDMA cellular handsets
• Portable computers including laptops and notebooks
• Personal Digital Assistants (PDAs)
• Portable cameras and video recorders

Voltage Regulators - Linear, Low Drop Out (LDO) Regulators Procurement Notes

Verify the specific suffix '285' confirms the 2.85V fixed output voltage variant. Confirm the 'S' package designation corresponds to the SOT-23-5 form factor. Ensure the 'X' suffix matches the required tape and reel packaging quantity of 3000 units per reel. Cross-reference the manufacturer part number against official datasheets to confirm the ERR pin functionality is present rather than the ADJ or BYP configurations found in other family members.

Voltage Regulators - Linear, Low Drop Out (LDO) Regulators Selection Notes

Select this component when a stable 2.85V rail is required for battery-powered portable electronics. The FAN2509S285X is appropriate for designs needing fault monitoring via the ERR pin to detect undervoltage conditions. Consider the 50mA current limit and the requirement for external input and output capacitors to ensure loop stability. Evaluate the thermal resistance characteristics relative to the PCB copper area to manage heat dissipation under maximum load conditions.

Voltage Regulators - Linear, Low Drop Out (LDO) Regulators Part Context

This device belongs to the FAN2508/FAN2509 family of 50mA CMOS LDO regulators. While the FAN2508 offers adjustable or bypass options on Pin 4, the FAN2509 specifically assigns Pin 4 to an Error Flag output. This family replaces older BiCMOS designs, offering improved cost-effectiveness and compatibility with compact surface-mount packages suitable for space-constrained mobile applications.

Voltage Regulators - Linear, Low Drop Out (LDO) Regulators Replacement Considerations

Direct substitutes within the same family include the FAN2509S28X (2.8V) and FAN2509S30X (3.0V). Other variants like FAN2508S285X share the physical package but differ in Pin 4 functionality, utilizing a Bypass pin instead of an Error Flag.

Voltage Regulators - Linear, Low Drop Out (LDO) Regulators FAQ

What is the function of Pin 4 on the FAN2509S285X?

Pin 4 is designated as ERR, an open-drain error flag output. It indicates a fault condition by going LOW when the output voltage drops below 95% of the nominal rated voltage.

How does the device handle thermal overload?

The regulator includes onboard thermal protection. If the die temperature exceeds 150°C, the output shuts down. The output remains suspended until the temperature drops below this limit, at which point it re-enables.

What is the shutdown current when the Enable pin is deactivated?

Applying a voltage of 0.4V or less to the Enable pin disables the output, reducing the supply current to less than 1µA.