LTC4278 - IEEE 802.3at PD with Synchronous No-Opto Flyback Controller and 12V Aux Support


  • 25.5W IEEE 802.3at Compliant (Type 2) PD
  • 10V to 57V Auxiliary Power Input
  • Shutdown Pin for Flexible Auxiliary Power Support
  • Integrated State-of-the-Art No-Opto Synchronous Flyback Controller
  • – Isolated Power Supply Efficiency >92%
    – 88% Efficiency Including Diode Bridge and Hot Swap™ FET
  • Superior EMI Performance
  • Robust 100V 0.7Ω (Typ) Integrated Hot Swap MOSFET
  • IEEE 802.3at High Power Available Indicator
  • Integrated Signature Resistor and Programmable Class Current
  • Undervoltage, Overvoltage and Thermal Protection
  • Short-Circuit Protection with Auto-Restart
  • Programmable Soft-Start and Switching Frequency
  • Complementary Power Good Indicators
  • Thermally Enhanced 7mm × 4mm DFN Package

Typical Application

LTC4278 Typical Application


The LTC4278 is an integrated Powered Device (PD) controller and switching regulator intended for high power IEEE 802.3at and 802.3af applications. With a wide input voltage range, the LTC4278 is specifically designed to support PD applications that include a low-voltage auxiliary power input such as a 12V wall adaptor. The inclusion of a shutdown pin provides simple implementation of both PoE and auxiliary dominate applications. In addition, the LTC4278 supports both 1-event and 2-event classifications as defined by the IEEE, thereby allowing the use in a wide range of product configurations.

The LTC4278 synchronous, current mode, flyback controller generates multiple supply rails in a single conversion step providing for the highest system efficiency while maintaining tight regulation across all outputs. The LTC4278 includes Linear Technology’s patented No-Opto feedback topology to provide full IEEE 802.3 isolation without the need of an opto-isolator circuit. A true soft-start function allows graceful ramp-up of all output voltages.

The LTC4278 is available in a space saving 32-pin DFN package.


CAD Symbols and Footprints: The downloadable Zip file below contains the schematic symbol and PCB footprints.

For complete and up to date package information and drawings, please refer to our packaging page

Part Number Package Code Temp Package
LTC4278CDKD#PBF 7x4 DFN-32 DKD C 05-08-1734 Yes
LTC4278CDKD#TRPBF 7x4 DFN-32 DKD C 05-08-1734 Yes
LTC4278IDKD#PBF 7x4 DFN-32 DKD I 05-08-1734 Yes
LTC4278IDKD#TRPBF 7x4 DFN-32 DKD I 05-08-1734 Yes

LTC4278 Package Drawing

Order Info

  • Part numbers ending in PBF are lead free. Solder plated terminal finish (SnPb) versions are non-standard and special terms and conditions and pricing applies if available. Please contact LTC marketing for information.
  • Part numbers containing TR or TRM are shipped in tape and reel or 500 unit mini tape and reel, respectively
  • Please refer to our general ordering information or the product datasheet for more details

Package Variations and Pricing

Part Number Package Temp Price
LTC4278CDKD#PBF 7x4 DFN-32 C $3.71 $2.60 Yes
LTC4278CDKD#TRPBF 7x4 DFN-32 C $2.66 Yes
LTC4278IDKD#PBF 7x4 DFN-32 I $4.46 $3.12 Yes
LTC4278IDKD#TRPBF 7x4 DFN-32 I $3.18 Yes
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* The USA list pricing shown is for BUDGETARY USE ONLY, shown in United States dollars (FOB USA per unit for the stated volume), and is subject to change. International prices may differ due to local duties, taxes, fees and exchange rates. For volume-specific price or delivery quotes, please contact your local Linear Technology sales office or authorized distributor.

Demo Boards

Linear Technology offers many demo boards free of charge to qualified customers. Contact your local sales office or distributor to inquire about a demo board. Certain demo boards are also available for sale via credit card on this website. Demo boards are for evaluation purposes only. It remains the customer’s responsibility to verify proper and reliable operation in the actual end application.

Part Number Description Price Documentation
DC1561B LTC4278 IEEE802.3at PD Controller with 12V Aux, Vout = 5V, Iout = 4.5A $75.00
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Click here to view our complete list of demo boards


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