Features

• Compliant with IEEE 802.3at Type 1 and 2
• Supports LTPoE++® Up to 90W
• Supports Dual-Signature PDs
• Fully Autonomous Operation without Microcontroller
• Very Low Power Dissipation
  – 0.1Ω Sense Resistance
  – Low R_DS(ON) External MOSFET
• Very High Reliability 4-Point PD Detection
  – 2-Point Forced Voltage and Forced Current
• Robust Short-Circuit Protection
• Cable Surge Protected ±80V OUT pin
• Classification Dependent I_CUT and I_LIM Current Thresholds
• Supports 2-Pair and 4-Pair Output Power
• UltraPWR Mode Supports Custom PDs up to 123W
• Pin-Selectable Detection Backoff Timer for Midspans
• Pin Programmable Legacy PD Detection
• Pin Programmable Maximum Power Mode
• Status LED Pin
• Available in 20-Pin QFN and 16-Pin SO Packages

Typical Application

Description

The LTC®4279 is an autonomous single port power sourcing equipment (PSE) controller designed for use in IEEE 802.3at Type 1, Type 2 and LTPoE++ compliant Power over Ethernet (PoE) systems. The LTC4279 provides fully autonomous IEEE 802.3 and LTPoE++ compliant operation without a microcontroller. The LTC4279 simplifies PSE implementation, requiring only a single supply and a small number of passive support components.

The LTC4279 delivers lowest-in-industry heat dissipation by utilizing a low-R_DS(ON) external MOSFET and a 0.1Ω sense resistor, eliminating the need for expensive heat sinks and increasing efficiency.

PD discovery uses a proprietary dual-mode 4-point detection mechanism ensuring excellent immunity from false PD detection. Midspan PSEs are supported with physical layer classification and a 2.5 second backoff timer.

Legacy and custom PDs are supported with pin-selectable LEGACY and UltraPWR modes. LEGACY mode detects and powers pre-IEEE specification PDs. UltraPWR mode aggressively turns on and powers custom PDs requiring high inrush and/or operational currents.