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LT4276 - LTPoE++/PoE+/PoE PD Forward/Flyback Controller

LT4276 - LTPoE++/PoE+/PoE PD Forward/Flyback Controller
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LT4276 - LTPoE++/PoE+/PoE PD Forward/Flyback Controller - 1

LT4276 LTPoE++/PoE+/PoE PD Forward/Flyback Controller Features IEEE802.3af/at and LTPoE++™ 90W Powered Device (PD) with Forward/Flyback Controller n LT4276A Supports All of the Following Standards: n LTPoE++ 38.7W, 52.7W, 70W and 90W n IEEE 802.3at 25.5W Compliant n IEEE 802.3af up to 13W Compliant n LT4276B is IEEE 802.3at/af Compliant n LT4276C is IEEE 802.3af Compliant n Superior Surge Protection (100V Absolute Maximum) n Wide Junction Temperature Range (–40°C to 125°C) n Auxiliary Power Support as Low as 9V n No Opto-Isolator Required for Flyback Operation n External Hot Swap™ N-Channel MOSFET for Lowest Power Dissipation and Highest System Efficiency n >94% End-to-End Efficiency with LT4321 Ideal Bridge n Available in a 28-Lead 4mm × 5mm QFN Package The LT®4276 is a pin-for-pin compatible family of IEEE 802.3 and LTPoE++ Powered Device (PD) controllers. It includes an isolated switching regulator controller capable of synchronous operation in both forward and flyback topologies with auxiliary power support. The LT4276A employs the LTPoE++ classification scheme, receiving 38.7W, 52.7W, 70W or 90W of power at the PD RJ45 connector, and is backwards compatible with IEEE 802.3. The LT4276B is a fully 802.3at compliant, 25.5W Type 2 (PoE+) PD. The LT4276C is a fully 802.3af compliant, 13W Type 1 (PoE) PD. The LT4276 supports both forward and flyback power supply topologies, configurable for a wide range of PoE applications. The flyback topology supports No-Opto feedback. Auxiliary input voltage can be accurately sensed with just a resistor divider connected to the AUX pin. The LT4276 utilizes an external, low RDS(ON) N-channel MOSFET for the Hot Swap function, maximizing power delivery and efficiency, reducing heat dissipation, and easing the thermal design. High Power Wireless Data Systems Outdoor Security Camera Equipment Commercial and Public Information Displays High Temperature Applications L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and LTPoE++, and Hot Swap are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. LTPoE++ 70W Power Supply in a Forward Mode MAX DELIVERED POWER A ++ 90W l LTPoE l LTPoE++ 70W LTPoE++ 52.7W LTPoE++ 38.7W LT4276A RCLASS RCLASS++ GND FB31 SS ROSC

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LT4276 - LTPoE++/PoE+/PoE PD Forward/Flyback Controller - 2

LT4276 Absolute Maximum Ratings UFD PACKAGE 28-LEAD (4mm × 5mm) PLASTIC QFN TJMAX = 150°C, θJC = 3.4°C/W EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB *RCLASS++ is not connected in the LT4276B and LT4276C **T2P is not connected in the LT4276C Order Information LEAD FREE FINISH PART MARKING* MAX PD POWER PACKAGE DESCRIPTION TEMPERATURE RANGE Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for information on nonstandard lead based finish parts. For more...

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LT4276 - LTPoE++/PoE+/PoE PD Forward/Flyback Controller - 3

The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ = 25°C. VVPORT = VHSSRC = VVIN = 40V, VVCC = VCCREG, ROSC, PG, and SG Open, RFFSDLY = 5.23kΩ to GND. AUX connected to GND unless otherwise specified. (Note 2) SYMBOL VPORT, HSSRC, VIN Operating Voltage VPORT Signature Range VPORT Classification Range VPORT Mark Range At VPORT Pin, After 1st Classification Event Signature/Class Hysteresis Window Reset Threshold Hot Swap Turn-On Voltage Hot Swap Turn-Off Voltage Hot Swap On/Off Hysteresis Window Supply Current VPORT,...

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LT4276 - LTPoE++/PoE+/PoE PD Forward/Flyback Controller - 4

The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ = 25°C. VVPORT = VHSSRC = VVIN = 40V, VVCC = VCCREG, ROSC, PG, and SG Open, RFFSDLY = 5.23kΩ to GND. AUX connected to GND unless otherwise specified. (Note 2) SYMBOL PG, SG Output High Level PG Rise Time, Fall Time SG Rise Time, Fall Time Current Sense/Overcurrent VFAULT Overcurrent Fault Threshold ΔVSENSE/ ΔVITHB Current Sense Comparator Threshold with Respect to VITHB VISEN+ - VISEN– VITHB Offset Timing fOSC Default Switching Frequency Switching Frequency LTPoE++...

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LT4276 - LTPoE++/PoE+/PoE PD Forward/Flyback Controller - 5

LT4276 Typical Performance Characteristics Input Current vs Input Voltage 25k Detection Range Signature Resistance vs Input Voltage Switching Frequency vs Temperature Feedback Amplifier Output Current vs VFB31 ROSC OPEN Current Sense Voltage vs Duty Cycle, ITHB PG Delay Time vs Temperature in Forward Mode PG Delay Time vs Temperature in Flyback Mode

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LT4276 - LTPoE++/PoE+/PoE PD Forward/Flyback Controller - 6

LT4276 Pin Functions GND(Pins 1, 19, Exposed Pad Pin 29): Device Ground. Exposed Pad must be electrically and thermally connected to PCB GND and Pin 19. RCLASS++ (Pin 3, LT4276A Only): LTPoE++ Class Select Input. Connect a resistor between RCLASS++ to GND per Table 1. AUX (Pin 2): Auxiliary Sense. Assert AUX via a resistive divider from the auxiliary power input to set the voltage at which the auxiliary supply takes over. Asserting AUX pulls down HSGATE, disconnects the signature resistor and disables classification. The AUX pin sinks IAUXH when below its threshold voltage of VAUXT to...

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LT4276 - LTPoE++/PoE+/PoE PD Forward/Flyback Controller - 7

LT4276 Block Diagram VPORT START-UP REGULATOR INTERNAL BUCK CONTROLLER HSSRC VPORT SWITCHING REGULATOR CONTROLLER LOAD COMP SLOPE COMP ∆VSENSE ∆VITHB CURRENT SENSE COMPARATOR CURRENT FAULT COMPARATOR

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LT4276 - LTPoE++/PoE+/PoE PD Forward/Flyback Controller - 8

LT4276 Applications Information OVERVIEW Power over Ethernet (PoE) continues to gain popularity as products take advantage of DC power and high speed data available from a single RJ45 connector. The LT4276A allows higher power while maintaining backwards compatibility with existing PSE systems. The LT4276 combines a PoE PD controller and a switching regulator controller capable of either flyback or forward isolated power supply operation. ∆VSENSE ∆VITHB SIGNIFICANT DIFFERENCES FROM PREVIOUS PRODUCTS The LT4276 has several significant differences from previous Linear Technology products....

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LT4276 - LTPoE++/PoE+/PoE PD Forward/Flyback Controller - 9

LT4276 Applications Information Detection During detection, the PSE looks for a 25kΩ signature resistor which identifies the device as a PD. The LT4276 signature resistor is smaller than 25k to compensate for the additional series resistance introduced by the IEEE required bridge. VHSON VHSOFF CLASS VCLASSMIN VSIGMAX Classification The detection/classification process varies depending on whether the PSE is Type 1, Type 2, or LTPoE++. A Type 1 PSE, after a successful detection, may apply a classification probe voltage of 15.5V to 20.5V and measure current. VRESET VSIGMIN POWER ON VHSON...

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