Features

• IEEE 802.3af/at and LTPoE++™ Powered Device (PD) Controller
• LTPoE++ Supports Power Levels Up to 90W
• LT4275A Supports All of the Following Standards:
  LTPoE++ 38.7W, 52.7W, 70W and 90W
  IEEE 802.3at 25.5W Compliant
  IEEE 802.3af Up to 13W Compliant
• LT4275B is IEEE 802.3at/af Compliant
• LT4275C is IEEE 802.3af Compliant
• 100V Absolute Maximum Input Voltage
• Wide Junction Temperature Range (–40°C to 125°C)
• Overtemperature Protection
• Integrated Signature Resistor
• External Hot Swap™ N-Channel MOSFET for Lowest Power Dissipation and Highest System Efficiency
• Programmable Aux Power Support as Low as 9V
• Optional Support of Non-Standard Low Voltage PoE
• Available in 10-Lead MSOP and 3mm × 3mm DFN Packages

Typical Application

Description

The LT®4275 is a pin-for-pin compatible family of IEEE 802.3 and LTPoE++ powered device (PD) controllers.

The LT4275A employs a proprietary LTPoE++ classification scheme, delivering 38.7W, 52.7W, 70W or 90W of power at the PD RJ45 connector. The LT4275A is fully compatible with IEEE 802.3. The LT4275B is an IEEE 802.3at compliant, Type 2 (PoE+) PD delivering up to 25.5W. The LT4275C is an IEEE 802.3af compliant, Type 1 (PoE) PD delivering up to 13W.

The LT4275 internal charge pump provides an N-channel MOSFET solution, eliminating a larger and more costly P-channel MOSFET. A low R_DS(ON) MOSFET also maximizes power delivery and efficiency, reduces power and heat dissipation, and eases thermal design. Startup inrush current is adjustable with an external capacitor. The LT4275 also includes a power good output, on-board signature resistor, undervoltage lockout, and thermal protection. The LT4275A/LT4275B drives a single opto-coupler to indicate the power level of the attached PSE. Pin-selectable support for non-standard low voltage operation is provided. Auxiliary power override is supported with the AUX pin.

The LT4275A can be configured to support all possible LTPoE++, 802.3at and 802.3af power levels with external component changes.