LT4276 LTPoE++/PoE+/PoE PD Forward/Flyback Controller Description Features n n n n n n n n n n n IEEE802.3af/at and LTPoE++TM 90W Powered Device (PD) with Forward/Flyback Controller LT4276A Supports All of the Following Standards: nn LTPoE++ 38.7W, 52.7W, 70W and 90W nn IEEE 802.3at 25.5W Compliant nn IEEE 802.3af up to 13W Compliant LT4276B is IEEE 802.3at/af Compliant LT4276C is IEEE 802.3af Compliant Superior Surge Protection (100V Absolute Maximum) Wide Junction Temperature Range (-40C to 125C) Auxiliary Power Support as Low as 9V No Opto-Isolator Required for Flyback Operation External Hot SwapTM N-Channel MOSFET for Lowest Power Dissipation and Highest System Efficiency >94% End-to-End Efficiency with LT4321 Ideal Bridge Available in a 28-Lead 4mm x 5mm QFN Package Applications n n n n The LT(R)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, LTPoE++, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Typical Application AUX 37V-57V VPORT LTPoE++ 70W Power Supply in a Forward Mode + LT4276 Family - + - 22F FMMT723 0.1F * + 100H 3.3k 10nF VPORT HS GATE AUX * 5V 13A - BAV19WS (TRR 50ns) 10F VIN HS SW SRC VCC VCC FFS PG DLY ISEN+ VCC 20m LT4276A ISEN- RCLASS RCLASS++ GND FB31 SS ROSC + SG T2P ITHB 0.1F 10k 100pF MAX DELIVERED POWER A ++ l LTPoE 90W l LTPoE++ 70W LTPoE++ 52.7W LTPoE++ 38.7W LT4276 GRADE B C l l 25.5W l l 13W l l l 4276 TA01 OPTO 100k TO MICROPROCESSOR 4276fa For more information www.linear.com/LT4276 1 LT4276 Absolute Maximum Ratings Pin Configuration (Notes 1, 2) SWVCC VIN HSSRC HSGATE NC VPORT TOP VIEW 28 27 26 25 24 23 GND 1 22 DNC AUX 2 21 VCC RCLASS++/NC* 3 20 PG 29 GND RCLASS 4 T2P/NC** 5 19 GND 18 SG 17 ISEN+ VCC 6 VCC 7 16 ISEN- VCC 8 15 RLDCMP FB31 ITHB FFSDLY SFST VCC 9 10 11 12 13 14 ROSC VPORT, HSSRC, VIN Voltages......................-0.3 to 100V HSGATE Current.................................................. 20mA VCC Voltage..................................................... -0.3 to 8V RCLASS, RCLASS++ Voltages..................................-0.3 to 8V (and VPORT) SFST, FFSDLY, ITHB, T2P Voltages.......-0.3 to VCC+0.3V ISEN+, ISEN - Voltages............................................0.3V FB31 Voltage...................................................+12V/-30V RCLASS/RCLASS++ Current............................... -50mA AUX Current......................................................... 1.4mA ROSC Current...................................................... 100A RLDCMP Current.................................................500A T2P Current..........................................................-2.5mA Operating Junction Temperature Range (Note 3) LT4276AI/LT4276BI/LT4276CI...............-40C to 85C LT4276AH/LT4276BH/LT4276CH........ -40C to 125C Storage Temperature Range................... -65C to 150C UFD PACKAGE 28-LEAD (4mm x 5mm) PLASTIC QFN TJMAX = 150C, JC = 3.4C/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 TAPE AND REEL PART MARKING* MAX PD POWER PACKAGE DESCRIPTION TEMPERATURE RANGE LT4276AIUFD#PBF LT4276AIUFD#TRPBF 4276A 90W 28-Lead (4mm x 5mm) Plastic QFN -40C to 85C LT4276AHUFD#PBF LT4276AHUFD#TRPBF 4276A 90W 28-Lead (4mm x 5mm) Plastic QFN -40C to 125C LT4276BIUFD#PBF LT4276BIUFD#TRPBF 4276B 25.5W 28-Lead (4mm x 5mm) Plastic QFN -40C to 85C LT4276BHUFD#PBF LT4276BHUFD#TRPBF 4276B 25.5W 28-Lead (4mm x 5mm) Plastic QFN -40C to 125C LT4276CIUFD#PBF LT4276CIUFD#TRPBF 4276C 13W 28-Lead (4mm x 5mm) Plastic QFN -40C to 85C LT4276CHUFD#PBF LT4276CHUFD#TRPBF 4276C 13W 28-Lead (4mm x 5mm) Plastic QFN -40C to 125C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix. 2 4276fa For more information www.linear.com/LT4276 LT4276 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ = 25C. VVPORT = VHSSRC = VVIN = 40V, VVCC = VCCREG, ROSC, PG, and SG Open, RFFSDLY = 5.23k to GND. AUX connected to GND unless otherwise specified. (Note 2) SYMBOL PARAMETER CONDITIONS MIN VPORT, HSSRC, VIN Operating Voltage At VPORT Pin l TYP MAX 60 UNITS V VSIG VPORT Signature Range At VPORT Pin l 1.5 10 V VCLASS VPORT Classification Range At VPORT Pin l 12.5 21 V VMARK VPORT Mark Range At VPORT Pin, After 1st Classification Event l 5.6 10 V VPORT AUX Range At VPORT Pin, VAUX 6.45V l 8 60 V Signature/Class Hysteresis Window l 1.0 2.6 Reset Threshold l VHSON Hot Swap Turn-On Voltage l VHSOFF Hot Swap Turn-Off Voltage l 30 Hot Swap On/Off Hysteresis Window l 3 V 35 5.6 V 37 V 31 V V Supply Current VPORT, HSSRC & VIN Supply Current VVPORT = VHSSRC = VVIN = 60V VPORT Supply Current During Classification VVPORT = 17.5V, RCLASS, RCLASS++ Open 2 mA 1.3 mA 2.2 mA 24.4 25.5 k 5.2 8.3 11.4 k 1.36 1.40 1.43 V l l 0.7 VVPORT = VMARK after 1st Classification Event l 0.4 Signature Resistance VSIG (Note 4) l 23.6 Signature Resistance During Mark Event RCLASS/RCLASS++ Voltage VMARK (Note 4) l -10mA IRCLASS -36mA l Classification Stability Time VVPORT Step to 17.5V, RCLS = 35.7 l VPORT Supply Current During Mark Event 1.0 Signature and Classification 2 ms Digital Interface VAUXT AUX Threshold VPORT = 17.5V, VIN = VHSSRC = 18.5V l 6.05 6.25 6.45 V IAUXH AUX Pin Current VAUX = 6.05V, VPORT = 17.5V, VIN = 9V, VCC = 0V l 3.3 5.3 7.3 A T2P Output High VVCC - VT2P, -1mA Load l T2P Leakage VT2P = 0V l -1 HSGATE Pull Up Current VHSGATE - VHSSRC = 5V (Note 5) l -27 HSGATE Voltage -10A Load, with respect to HSSRC l 10 HSGATE Pull Down Current VHSGATE - VHSSRC = 5V l 400 l 7.2 7.6 8.0 V l 3.11 3.17 3.23 V 0.3 V 1 A -18 A 14 V Hot Swap Control IGPU -22 A VCC Supply VCCREG VCC Regulation Voltage Feedback Amplifier VFB FB31 Regulation Voltage FB31 Pin Bias Current RLDCMP Open gm Feedback Amplifier Average TransConductance Time Average, -2A < IITHB < 2A l -52 -0.1 -40 -26 A/V A ISINK ITHB Average Sink Current Time Average, VFB31 = 0V l 4.4 8.0 13.4 A Charging Current VSFST = 0.5V, 3.0V l -49 -42 -36 A Soft-Start ISFST 4276fa For more information www.linear.com/LT4276 3 LT4276 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ = 25C. VVPORT = VHSSRC = VVIN = 40V, VVCC = VCCREG, ROSC, PG, and SG Open, RFFSDLY = 5.23k to GND. AUX connected to GND unless otherwise specified. (Note 2) SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Gate Outputs VCC -0.1 V PG, SG Output High Level I = -1mA l PG, SG Output Low Level I = 1mA l PG Rise Time, Fall Time PG = 1000pF 15 ns SG Rise Time, Fall Time SG = 400pF 15 ns 1 V Current Sense/Overcurrent VFAULT Overcurrent Fault Threshold l 125 140 155 mV VSENSE/ VITHB Current Sense Comparator Threshold with Respect to VITHB VISEN+ - VISEN- l -130 -111 -98 mV/V VITHB(OS) VITHB Offset l 3.03 3.17 3.33 V Timing fOSC Default Switching Frequency ROSC Pin Open l 200 214 223 kHz ROSC = 45.3k to GND l 280 300 320 kHz fT2P Switching Frequency LTPoE++ Signal Frequency tMIN Minimum PG On Time l 175 250 330 ns DMAX Maximum PG Duty Cycle l 63 66 70 % tPGDELAY PG Turn-On Delay-Flyback PG Turn-On Delay-Forward fSW/256 5.23k from FFSDLY to GND 52.3k from FFSDLY to GND 10.5k from FFSDLY to VCC 52.3k from FFSDLY to VCC 45 171 92 391 ns ns ns ns tFBDLY Feedback Amp Enable Delay Time 350 ns tFB Feedback Amp Sense Interval 550 ns tPGSG PG Falling to SG Rising Delay Time-Flyback PG Falling to SG Falling Delay TimeForward Resistor from FFSDLY to GND 10.5k from FFSDLY to VCC 52.3k from FFSDLY to VCC 20 67 301 ns ns ns tSTART Start Timer (Note 6) Delay After Power Good l 80 86 93 ms tFAULT Fault Timer (Note 6) Delay After Overcurrent Fault l 80 86 93 ms IMPS MPS Current l 10 12 14 mA Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2. All voltages with respect to GND unless otherwise noted. Positive currents are into pins; negative currents are out of pins unless otherwise noted. Note 3. This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature can exceed 150C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may impair device reliability. 4 Note 4. Signature resistance specifications do not include resistance added by the external diode bridge which can add as much as 1.1k to the port resistance. Note 5. IGPU available in PoE powered operation. That is, available after V(VPORT) > VHSON and V(AUX) < VAUXT, over the range where V(VPORT) is between VHSOFF and 60V. Note 6. Guaranteed by design, not subject to test. 4276fa For more information www.linear.com/LT4276 LT4276 Typical Performance Characteristics Input Current vs Input Voltage 25k Detection Range SIGNATURE RESISTANCE (k) 125C 85C 25C -40C 0.4 VPORT CURRENT (mA) 26.25 0.3 0.2 0.1 0 2 0 4 6 VPORT VOLTAGE (V) 8 125C 85C 25C -40C 25.75 10 300KHz 25.25 24.75 24.25 23.75 10 VCC Current vs Temperature 12 VCC CURRENT (mA) 0.5 Signature Resistance vs Input Voltage 214KHz 6 4 2 1 2 3 4 5 6 7 VPORT VOLTAGE (V) 8 4276 G01 0 -50 9 15 3.178 3.176 3.168 5 0 -5 125 325 ROSC = 45.3k 300 FREQUENCY (kHz) ITHB CURRENT (A) 3.170 100 Switching Frequency vs Temperature 125C 85C 25C -40C 10 3.172 0 25 50 75 TEMPERATURE (C) 4276 G03 Feedback Amplifier Output Current vs VFB31 3.174 -25 4276 G02 VFB31 vs Temperature VFB31 (V) 8 275 250 225 ROSC OPEN 3.166 200 -10 3.164 3.162 -50 -25 0 25 50 75 TEMPERATURE (C) 100 -15 2.57 125 2.77 2.97 3.17 3.37 FB31 VOLTAGE (V) Current Sense Voltage vs Duty Cycle, ITHB 250 350 100 80 VITHB = 2.3V 60 40 20 10 20 30 40 50 DUTY CYCLE (%) 100 TPGSG, RFFSDLY = 52.3k 250 200 150 TPGDELAY, RFFSDLY = 10.5k 100 RFFSDLY = 5.23k 50 VITHB = 2.9V 0 150 50 VITHB = 2.6V 60 70 4276 G07 0 -50 125 TPGDELAY, RFFSDLY = 52.3k 300 RFFSDLY = 52.3k DELAY TIME (ns) PG DELAY TIME (ns) VITHB = 1.8V 100 400 200 120 0 25 50 75 TEMPERATURE (C) PG Delay Time vs Temperature in Forward Mode VITHB = 0.96V (FB31 = 0V) 140 -25 4276 G06 PG Delay Time vs Temperature in Flyback Mode 160 V(ISEN+ - ISEN-) (mV) 175 -50 3.77 4276 G05 4276 G04 0 3.57 -25 0 25 50 75 TEMPERATURE (C) 100 125 4276 G08 0 -50 TPGSG, RFFSDLY = 10.5k -25 0 25 50 75 TEMPERATURE (C) 100 125 4276 G09 4276fa For more information www.linear.com/LT4276 5 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 provide hysteresis. Connect to GND if not used. RCLASS (Pin 4): Class Select Input. Connect a resistor between RCLASS to GND per Table 1. T2P (Pin 5, LT4276A and LT4276B only): PSE Type Indicator. Low impedance to VCC indicates 2-event classification. Alternating low/high impedance indicates LTPoE++ classification (LT4276A only, see Applications Information). High impedance indicates 1-event classification. This pin is not connected on the LT4276C. See the Applications Information Section for pin behavior when using the AUX pin. DNC (Pin 22): Do Not Connect. Leave pin open. ROSC (Pin 10): Programmable Frequency Adjustment. Resistor to GND programs operating frequency. Leave open for default frequency of 214kHz. SFST (Pin 11): Soft-Start. Capacitor to GND sets softstart timing. FFSDLY (Pin 12): Forward/Flyback Select and Primary Gate Delay Adjustment. Resistor to GND adjusts gate drive delay for a flyback topology. Resistor to VCC adjusts gate drive delay for a forward topology. ITHB (Pin 13): Current Threshold Control. The voltage on this pin corresponds to the peak current of the external 6 FET. Note that the voltage gain from ITHB to the input of the current sense comparator (VSENSE) is negative. FB31 (Pin 14): Feedback Input. In flyback mode, connect external resistive divider from the third winding feedback. Reference voltage is 3.17V. Connect to GND in forward mode. RLDCMP (Pin 15): Load Compensation Adjustment. Optional resistor to GND controls output voltage set point as a function of peak switching current. Leave RLDCMP open if load compensation is not needed. ISEN- (Pin 16): Current Sense, Negative Input. Route as a dedicated trace to the current sense resistor. ISEN+ (Pin 17): Current Sense, Positive Input. Route as a dedicated trace to the current sense resistor. SG (Pin 18): Secondary (Synchronous) Gate Drive, Output. PG (Pin 20): Primary Gate Drive, Output. VCC (Pins 6, 7, 8, 9, 21): Switching Regulator Controller Supply Voltage. Connect a local 1F ceramic capacitor from VCC pin 21 to GND pin 19 as close as possible to LT4276 as shown in Table 2. SWVCC(Pin 23): Switch Driver for VCC's Buck Regulator. This pin drives the base of a PNP in a buck regulator to generate VCC. VIN (Pin 24): Buck Regulator Supply Voltage. Usually separated from HSSRC by a pi filter. HSSRC (Pin 25): External Hot Swap MOSFET Source. Connect to source of the external MOSFET. HSGATE (Pin 26): External Hot Swap MOSFET Gate Control, Output. Capacitance to GND determines inrush time. NC (Pin 27): No Connection. Not internally connected. VPORT (Pin 28): PD Interface Supply Voltage and External Hot Swap MOSFET Drain Connection. 4276fa For more information www.linear.com/LT4276 LT4276 Block Diagram VPORT VIN SWVCC START-UP REGULATOR INTERNAL BUCK CONTROLLER CP HSGATE VCC 11V VCC PD INTERFACE CONTROLLER HSSRC VPORT - + - + RCLASS T2P 1.4V 1.4V TSD GND VPORT RCLASS++ PG SG + - AUX VAUXT IAUXH FB31 VFB + - ITHB VCC FEEDBACK AMP gm = -40A/V SFST SWITCHING REGULATOR CONTROLLER LOAD COMP FFSDLY OSC + - VFAULT + - - + AV = 10 AV = SLOPE COMP VSENSE VITHB VSENSE AV = 1 ISEN+ - + CURRENT SENSE COMPARATOR - + CURRENT FAULT COMPARATOR ROSC VITHB(OS) 4276 BD ISEN- RLDCMP 4276fa For more information www.linear.com/LT4276 7 LT4276 Applications Information OVERVIEW VSENSE 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 VITHB(OS) VITHB 4276 F01 SIGNIFICANT DIFFERENCES FROM PREVIOUS PRODUCTS The LT4276 has several significant differences from previous Linear Technology products. These differences are briefly summarized below. See Applications Information for more detail. ITHB Is Inverted from the Usual ITH pin Figure 1. VSENSE vs. VITHB Flyback/Forward Mode Is Pin Selectable The LT4276 operates in flyback mode if FFSDLY is pulled down by a resistor to GND. It operates in forward mode if FFSDLY is pulled up by a resistor to VCC. The value of this resistor determines the tPGDELAY and tPGSG. The ITHB pin voltage has an inverse relationship to the current sense comparator threshold, VSENSE. Furthermore, the ITHB pin offset voltage, VITHB(OS), is 3.17V. See Figure 1. T2P Pin Polarity Is Reversed Duty-Cycle Based Soft-Start VCC Is Powered by Internally Driven Buck Regulator The LT4276 uses a duty cycle ramp soft-start that injects charge into ITHB. This allows startup without appreciable overshoot and with inexpensive external components. The Feedback Pin (FB31) is 3.17V rather than 1.25V The error amp feedback voltage (VFB) is 3.17V. The T2P pin pulls up to VCC when active rather than pulling down to GND. The LT4276 includes a buck regulator controller that must be used to generate the VCC supply voltage. PoE MODES OF OPERATION The LT4276 has several modes of operation, depending on the input voltage sequence applied to the VPORT pin. Table 1. Classification Codes, Power Levels and Resistor Selection PD POWER NOMINAL CLASS CLASS AVAILABLE PD TYPE CURRENT 0 13W Type 1 0.7mA 1 3.84W Type 1 10.5mA 2 6.49W Type 1 18.5mA 3 13W Type 1 28mA 4 25.5W Type 2 40mA 4* 38.7W LTPoE++ 40mA 4* 52.7W LTPoE++ 40mA 4* 70W LTPoE++ 40mA 4* 90W LTPoE++ 40mA *An LTPoE++ PD classifies as class 4 by an IEEE 802.3 compliant PSE. 8 A LT4276 GRADE CAPABILITY B C RESISTOR (1%) RCLS RCLS++ Open Open 150 Open 80.6 Open 52.3 Open 35.7 Open Open 35.7 150 47.5 80.6 64.9 52.3 118 4276fa For more information www.linear.com/LT4276 LT4276 Applications Information Detection POWER ON During detection, the PSE looks for a 25k 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 VPORT 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 VHSOFF VPORT 1ST CLASS 2ND CLASS LTPoE++ Classification VCLASSMIN VSIGMAX The LT4276A allows higher power allocation while maintaining backwards compatibility with existing PSE systems by extending the classification signaling of IEEE 802.3. Linear Technology PSE controllers capable of LTPoE++ are listed in the Related Parts section. IEEE PSEs classify an LTPoE++ PD as a Type 2 PD. 1ST MARK 2ND MARK VSIGMIN 4276 F03 Figure 3. Type 2 Detect/Class Signaling Waveform POWER ON VHSON VHSOFF VPORT 1ST CLASS 2ND CLASS 3RD CLASS VCLASSMIN VSIGMAX VRESET VSIGMIN During the mark state, the LT4276 presents <11k to the port as required by the IEEE specification. DETECT VRESET Classification Resistors (RCLS and RCLS++) Signature Corrupt During Mark 4276 F02 Figure 2. Type 1 Detect/Class Signaling Waveform In 2-event classification, a Type 2 PSE probes for power classification twice as shown in Figure 3. The LT4276A or LT4276B recognizes this and pulls the T2P pin up to VCC to signal the load that Type 2 power is available. Otherwise it does not pull up on the T2P pin, indicating that only Type 1 power is available. If an LT4276A senses an LTPoE++ PSE it alternates between pulling T2P up and floating T2P at a rate of fT2P to indicate the LTPoE++ power is available. The RCLS and RCLS++ resistors set the classification current corresponding to the PD power classification. Select the value of RCLS from Table 1 and connect the resistor between the RCLASS pin and GND. For LTPoE++, use the LT4276A and select the value of RCLS++ from Table 1 in addition to RCLS. The resistor tolerance must be 1% or better to avoid degrading the overall accuracy of the classification circuit. DETECT DETECT 1ST MARK 2ND MARK 3RD MARK 4276 F04 Figure 4. LTPoE++ Detect/Class Signaling Waveform 4276fa For more information www.linear.com/LT4276 9 LT4276 Applications Information Inrush and Powered On EXTERNAL VCC SUPPLY Once the PSE detects and optionally classifies the PD, the PSE then powers on the PD. When the port voltage rises above the VHSON threshold, it begins to source IGPU out of the HSGATE pin. This current flows into an external capacitor (CGATE in Figure 5) that causes a voltage to ramp up the gate of the external MOSFET. The external MOSFET acts as a source follower and ramps the voltage up on the output bulk capacitor (CPORT in Figure 5), thereby determining the inrush current (IINRUSH in Figure 5). To meet IEEE requirements, design IINRUSH to be ~100mA. The external VCC supply must be configured as a buck regulator shown in Figure 6. To optimize the buck regulator, use the external component values in Table 2 corresponding to the VIN operating range. This buck regulator runs in discontinuous mode with the inductor peak current considerably higher than average load current on VCC. Thus, the saturation current rating of the inductor must exceed the values shown in Table 2. Place the capacitor, C, as close as possible to VCC pin 21 and GND pin 19. For optimal performance, place the external components as close as possible to the LT4276. The LT4276 internal charge pump provides an N-channel MOSFET solution, eliminating a larger and more costly P-channel FET. The low RDS(ON) MOSFET also maximizes power delivery and efficiency, reduces power and heat dissipation, and eases thermal design. VIN VIN Re LT4276 IINRUSH + VPORT 3.3k IGPU L(H) VCC GND CPORT VPORT CPORT CGATE VCC C(F) CGATE 4276 F06 Figure 6. VCC Buck Regulator HSGATE IINRUSH =IGPU * FMMT723 PBSS9110T SWVCC HSSRC Table 2 . Buck Regulator Component Selection LT4276 VIN 9V-57V PoE GND C 22F 10F L 22H 100H ISAT 1.2A 300mA Re 1 20 4276 F05 AUXILIARY SUPPLY OVERRIDE Figure 5. Programming IINRUSH DELAY START After the HSGATE charges up to approximately 7V above HSSRC, fully enhancing the external Hot Swap MOSFET, the switching regulator controller operates after a delay of tSTART. During this delay, the LT4276 draws IMPS from VPORT to ensure that the PSE does not DC disconnect the PD due to Maintain Power Signature requirements. If the AUX pin is held above VAUXT, the LT4276 enters auxiliary power supply override mode. In this mode the signature resistor is disconnected, classification is disabled, and HSGATE is pulled down. The T2P pin pulls up to VCC on the LT4276B (or the LT4276A when no RCLS++ resistor is present). The T2P pin alternates between pulling up and floating at fT2P on the LT4276A when the RCLS++ resistor is present. The AUX pin allows for setting the auxiliary supply turn on (VAUXON) and turn off (VAUXOFF) voltage thresholds. The auxiliary supply hysteresis voltage (VAUXHYS) is set by sinking current (IAUXH) only when the AUX pin voltage is 10 4276fa For more information www.linear.com/LT4276 LT4276 Applications Information less than VAUXT. Use the following equations to set VAUXON and VAUXOFF via R1 and R2 in Figure 7. A capacitor up to 1000pF may be placed between the AUX pin and GND to improve noise immunity. PG VAUXON must be lower than VHSOFF. SG R1= R2 = R1 VAUXON - VAUXOFF VAUXHYS = IAUXH IAUXH VAUX(MAX) - VAUXT 1.4mA tPGDELAY tPGSG + R1 VAUXOFF - 1 V AUXT tPGon 4276 F07 VAUX Figure 8: PG and SG Relationship in Flyback Mode LT4276 R1 * AUX R2 - + * GND 4276 F08a Figure 7. AUX Threshold and Hysteresis Calculation PG LT4276 ISEN+ SWITCHING REGULATOR CONTROLLER OPERATION The switching regulator controller portion of the LT4276 is a current mode controller capable of implementing either a flyback or a forward power supply. When used in flyback mode, no opto-isolator is required for feedback because the output voltage is sensed via the transformer's third winding. ISEN- GND FFSDLY SG RFFSDLY * * 4276 F08 Figure 9: Example PG and SG Connections in Flyback Mode Flyback Mode Forward Mode The LT4276 is programmed into flyback mode by placing a resistor RFFSDLY from the FFSDLY pin to GND. This resistor must be in the range of 5.23k to 52.3k. If using a potentiometer to adjust RFFSDLY, ensure the adjustment of the potentiometer does not exceed 52.3k.The value of RFFSDLY determines tPGDELAY according to the following equations: tPGDELAY 2.69ns / k *RFFSDLY + 30ns The LT4276 is programmed into forward mode by placing a resistor RFFSDLY from the FFSDLY pin to VCC. The RFFSDLY resistor must be in the range of 10.5k to 52.3k. If using a potentiometer to adjust RFFSDLY ensure the adjustment of the potentiometer does not exceed 52.3k. tPGSG 20ns The PG and SG relationships in flyback mode are shown in Figure 8. The SG pin must be connected to the secondary side MOSFET through a gate drive transformer as shown in Figure 9. Add a Schottky diode from PG to GND as shown in Figure 9 to prevent PG from going negative. The value of RFFSDLY determines tPGDELAY and tPGSG according to the following equations: tPGDELAY 7.16ns/k * RFFSDLY + 17ns tPGSG 5.60ns/k * RFFSDLY + 7.9ns The PG and SG relationships in forward mode are shown in Figure 10. 4276fa For more information www.linear.com/LT4276 11 LT4276 Applications Information RFB1 PG VFB RFB2 THIRD LT4276 FEEDBACK FB31 + - ITHB VIN * SECONDARY PRIMARY * SG tPGDELAY PG tPGSG 4276 F09 + - Figure 10: PG and SG relationship in Forward Mode AV = 10 + - VOUT * ISEN+ ISEN- RSENSE RLDCMP 4276 F11 RLDCMP VCC * * RFFSDLY VCC FFSDLY LT4276 Figure 12: Feedback and Load Compensation Connection PG ISEN+ FB31 VOLTAGE ISEN- GND VFB GND SG PG 4276 F10 Figure 11: Example PG and SG Connections in Forward Mode SG 4276 F09 tFBDLY tFB In forward mode, the SG pin has the correct polarity to drive the active clamp P-channel MOSFET through a simple level shifter as shown in Figure 11. Add a Schottky diode from the PG to GND as shown in Figure 11 to prevent PG from going negative. FEEDBACK AMPLIFIER In the flyback mode, the feedback amplifier senses the output voltage through the transformer's third winding as shown in Figure 12. The amplifier is enabled only during the fixed interval, tFB, as shown in Figure 13. This eliminates the opto-isolator in isolated designs, thus greatly improving the dynamic response and stability over lifetime. Since tFB is a fixed interval, the time-averaged transconductance, gm, varies as a function of the user-selected switching frequency. 12 Figure 13: Feedback Amplifier Timing Diagram FEEDBACK AMPLIFIER OUTPUT, ITHB As shown in the Block Diagram, VSENSE is the input of the Current Sense Comparator. VSENSE is derived from the output of a linear amplifier whose input is the voltage on the ITHB pin, VITHB. This linear amplifier inverts its input, VITHB, with a gain, VSENSE/VITHB, and with an offset voltage of VITHB(OS) to yield its output, VSENSE. This relationship is shown graphically in Figure 1. Note the slope VSENSE/VITHB is a negative number and is provided in the electrical characteristics table. V VITHB = VITHB(OS) + VSENSE * SENSE VITHB -1 4276fa For more information www.linear.com/LT4276 LT4276 Applications Information The block diagram shows VSENSE is compared against the voltage across the current sense resistor, V(ISEN+)V(ISEN-) modified by the internal slope compensation voltage discussed subsequently. LOAD COMPENSATION OPTO-ISOLATOR FEEDBACK As can be seen in Figure 13, the voltage on the FB31 pin droops slightly during the flyback period. This is mostly caused by resistances of components of the secondary side such as: the secondary winding, RDS(ON) of the synchronous MOSFET, ESR of the output capacitor, etc. These resistances cause a feedback error that is proportional to the current in the secondary loop at the time of feedback sample window. To compensate for this error, the LT4276 places a voltage proportional to the peak current in the primary winding on the RLDCMP pin. Where: VOUT is the desired change to VOUT RFB2 is the required change to RFB2 NTHIRD/NSECONDARY is the transformer third winding to secondary winding For forward mode operation, the flyback voltage cannot be sensed across the transformer. Thus, opto-isolator feedback must be used. When using opto-isolator feedback, connect the FB31 pin to GND and leave the RLDCMP pin open. In this condition, the feedback amplifier sinks an average current of ISINK into the ITHB pin. An example for feedback connections is shown in Figure 14. Note that since ISINK is time-averaged over the switching period, the sink current varies as a function of the user-selected switching frequency. Determining Feedback and Load Compensation Resistors Because the resistances of components on the secondary side are generally not well known, an empirical method must be used to determine the feedback and load compensation resistor values. VOUT VCC LT4276 ITHB GND RX FB31 INITIALLY SET RFB2 = 2k 4276 F13 V NTHIRD RFB1 RFB2 OUT -R VFB NSECONDARY FB2 Figure 14: Opto-isolator Feedback Connections in the Forward Mode Connect the resistor RLDCMP between the RLDCMP pin and GND. RLDCMP must be at least 10k. Adjust RLDCMP for minimum change of VOUT over the full input and output load range. A potentiometer in series with 10k may be initially used for RLDCMP and adjusted. The potentiometer+10k may then be removed, measured, and replaced with the equivalent fixed resistor. The resulting VOUT differs from the desired VOUT due to offset injected by load compensation. The change to RFB2 to correct this is predicted by: RFB2 = VOUT NTHIRD RFB22 VFB NSECONDARY RFB1 CX SOFT-START In PoE applications, a proper soft-start design is required to prevent the PD from drawing more current than the PSE can provide. The soft-start time, tSFST, is approximately the time in which the power supply output voltage, VOUT, is charging its output capacitance, COUT. This results in an inrush current at the port of the PD, Iport_inrush. Care must be taken in selecting tSFST to prevent the PD from drawing more current than the PSE can provide. 4276fa For more information www.linear.com/LT4276 13 LT4276 Applications Information In the absence of an output load current, the Iport_inrush, is approximated by the following equation: Iport_inrush (COUT * VOUT 2)/( * t SFST * VIN) where is the power supply efficiency, VIN is the input voltage of the PD Iport_inrush plus the port current due to the load current must be below the current the PSE can provide. Note that the PSE current capability depends on the PSE operating standard. The LT4276 contains a soft-start function that controls tSFST by connecting an external capacitor, CSFST, between the SFST pin and GND. The SFST pin is pulled up with ISFST when the LT4276 begins switching. The voltage ramp on the SFST pin is proportional to the duty cycle ramp for PG. For flyback mode, the soft-start time is: t SFST = 600A CSFST -t ) (t + t nF ISFST PGon PGDELAY MIN where tPGon is the time when PG is high as shown in Figure 8 once the power supply is in steady-state. In forward mode, each of the back page applications schematics provides a chart with tSFST vs. CSFST. Select the application and choose a value of CSFST that corresponds to the desired soft-start time. CURRENT SENSE COMPARATOR The LT4276 uses a differential current sense comparator to reduce the effects of stray resistance and inductance on the measurement of the primary current. ISEN+ and ISEN- must be Kelvin connected to the sense resistor pads. Like most switching regulator controllers, the current sense comparator begins sensing the current tMIN after PG turns on. Then, the comparator turns PG off after the voltage across ISEN+ and ISEN- exceeds the current sense comparator threshold, VSENSE. Note that the voltage across ISEN+ and ISEN- is modified by LT4276's internal slope compensation. SLOPE COMPENSATION The LT4276 incorporates current slope compensation. Slope compensation is required to ensure current loop stability when the duty cycle is greater than or near 50%. The slope compensation of the LT4276 does not reduce the maximum peak current at higher duty cycles. CONTROL LOOP COMPENSATION In flyback mode, loop frequency compensation is performed by connecting a resistor/capacitor network from the output of the feedback amplifier (ITHB pin) to GND as shown in Figure 12. In forward mode, loop compensation is performed by varying RX and CX in Figure 14. ADJUSTABLE SWITCHING FREQUENCY The LT4276 has a default switching frequency, fOSC, of 214 kHz when the ROSC pin is left open. If a higher switching frequency, fSW, is desired (up to 300 kHz), a resistor no smaller than 45.3k may be added between the ROSC pin to GND. The resistor can be calculated below: ROSC = 3900k *kHz (k ) ( fSW - fOSC ) SHORT CIRCUIT RESPONSE If the power supply output voltage is shorted, overloaded, or if the soft-start capacitor is too small, an overcurrent fault event occurs when the voltage across the sense pins exceeds VFAULT (after the blanking period of tMIN). This begins the internal fault timer tFAULT. For the duration of tFAULT, the LT4276 turns off PG and SG and pulls the SFST pin to GND. After tFAULT expires, the LT4276 initiates soft-start. The fault and soft-start sequence repeats as long as the short circuit or overload conditions persist. This condition is recognized by the PG waveform shown in Figure 15 repeating at an interval of tFAULT. tFAULT 4276 F14 Figure 15: PG Waveform with Output Shorted 14 4276fa For more information www.linear.com/LT4276 LT4276 Applications Information OVERTEMPERATURE PROTECTION The IEEE 802.3 specification requires a PD to withstand any applied voltage from 0V to 57V indefinitely. During classification, however, the power dissipation in the LT4276 may be as high as 1.5W. The LT4276 can easily tolerate this power for the maximum IEEE classification timing but overheats if this condition persists abnormally. The LT4276 includes an over-temperature protection feature which is intended to protect the device during momentary overload conditions. If the junction temperature exceeds the over-temperature threshold, the LT4276 pulls down HSGATE pin, disables classification, and disables the switching regulator operation. MAXIMUM DUTY CYCLE The maximum duty cycle of the PG pin is modified by the chosen tPGDELAY and fSW. It is calculated below: MAX POWER SUPPLY DUTY CYCLE = DMAX - tPGDELAY * fSW For high efficiency applications, the LT4276 supports an LT4321-based PoE ideal diode bridge that reduces the forward voltage drop from 0.7V to nearly 20mV per diode in normal operation, while maintaining IEEE 802.3 compliance. Auxiliary Input Diode Bridge Some PDs are required to receive AC or DC power from an auxiliary power source. A diode bridge is typically required to handle the voltage rectification and polarity correction. In high efficiency applications, the voltage drop across the rectifier cannot be tolerated. The LT4276 can be configured with an LT4320-based ideal diode bridge to recover the diode voltage drop and ease thermal design. Input Capacitor A 0.1F capacitor is needed from VPORT to GND to meet the input impedance requirement in IEEE 802.3 and to properly bypass the LT4276. This capacitor must be placed as close as possible to the VPORT and GND pins. Transient Voltage Suppressor For an appropriate margin during transient operation, the forward or flyback power supply should be designed so that its maximum steady-state duty cycle should be about 10% lower than the LT4276 Maximum Power Supply Duty Cycle calculated above. EXTERNAL INTERFACE AND COMPONENT SELECTION PoE Input Diode Bridge PDs are required to polarity-correct its input voltage. When diode bridges are used, the diode forward voltage drops affect the voltage at the VPORT pin. The LT4276 is designed to tolerate these voltage drops. The voltage parameters shown in the Electrical Characteristics are specified at the LT4276 package pins. The LT4276 specifies an absolute maximum voltage of 100V and is designed to tolerate brief overvoltage events due to Ethernet cable surges. To protect the LT4276, install a unidirectional transient voltage suppressor (TVS) such as an SMAJ58A between the VPORT and GND pins. This TVS must be placed as close as possible to the VPORT and GND pins of the LT4276. For PD applications that require an auxiliary power input, install a TVS between VIN and GND as close as possible to the LT4276. For extremely high cable discharge and surge protection contact Linear Technology Applications. 4276fa For more information www.linear.com/LT4276 15 LT4276 Typical Applications 13W (TYPE 1) PoE Power Supply in Flyback Mode with 5V, 2.3A Output L2 10H Q1 VPORT L1: COILCRAFT, DO1813P-181HC L2: COILCRAFT, DO1608C-103 L4: COILCRAFT, DO1608C-104 C2: 22F, 6.3V, MURATA GRM31CR70J226KE19 C5: 47F, 6.3V, PANASONIC 6SVP47M C7: 2.2F, 100V, MURATA GRM32ER72A225KA35 T1: WURTH, 750313109 Q1: PSMN075-100MSE T2: PCA EPA4271GE OR PULSE PE-68386NL + 10F 100V C7 2.2F * L1 180nH 3.3k 10nF 100V L4 100H * 47pF 630V 270 1/4W 20 FMMT723 6.04k VCC FB31 PG VIN SWVCC * -VOUT 11 1/4W ISEN+ 60m 1/4W MMBT3906 ISEN- PTVS58VP1UTP 52.3 SFST ROSC 5.23k 100 ITHB * * 4.7nF 330pF 1F 2.2nF T2 1F 107k 0.1F MMBT3904 15 SG GND RCLASS FFSDLY 10k BAT46WS 20k GND 2.2nF 2KV Efficiency vs Load Current 4276 TA02 Output Regulation vs Load Current 92 5.20 90 5.15 88 5.10 86 5.05 VOUT (V) EFFICIENCY (%) PSMN4R2-30MLD 1nF BAT54WS VPORT 0.1F 100V 84 82 80 5.00 4.95 4.90 VPORT = 37V VPORT = 48V VPORT = 57V 76 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 LOAD CURRENT (A) 4.85 VPORT = 37V VPORT = 48V VPORT = 57V 4.80 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 LOAD CURRENT (A) 4276 TA02a 16 VOUT 5V AT 2.3A FDN86246 LT4276C 78 C5 47F 6.3V T1 HSGATE 8.2 C2 22F 2k 10F BAV19WS 10V HSSRC 2.2nF 2kV 4276 TA02b 4276fa For more information www.linear.com/LT4276 SPARE PAIRS 8 5 7 4 6 2 3 DATA PAIRS 1 BG45 TG45 IN78 IN45 IN36 IN12 TG12 BG12 Q5 Q4 Q7 Q9 Q6 Q8 LT4321 Q3 For more information www.linear.com/LT4276 47nF 100V VPORT = 42.5V VPORT = 50V VPORT = 57V 4276 TA03a 0.1F ITHB VPORT = 42.5V VPORT = 50V VPORT = 57V 4276 TA03b 100 BAT54WS * * 1F T2 * 5.1 1/4W OPTO 2.2nF 2KV * * 1nF T1 2.2nF 2kV 40m 1/4W 160||160 1/4W 100pF 100V BSZ520N15NS3G 3.3nF 2k 5.90k 20k T2P SG ISEN- ISEN+ VCC FB31 PG 220pF 107k ROSC 10F 10V VOUT vs Load Current 7.50k SFST LT4276B BAV19WS L4 100H 4.80 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 LOAD CURRENT (A) 4.85 4.90 4.95 5.00 5.05 5.10 5.15 5.20 20 FMMT723 FFSDLY 35.7 GND RCLASS VPORT VIN SWVCC C7 2.2F HSSRC HSGATE 47nF 100V 10F 100V PTVS58VP1UTP 8.2 10nF 100V Efficiency vs Load Current 24V 3.3k + 78 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 LOAD CURRENT (A) 80 82 84 86 88 90 92 94 EN OUTN TG78 BG78 EN OUTP BG36 TG36 Q1 L2 10H VOUT (V) Q2 EFFICIENCY (%) L1: COILCRAFT, DO1813P-181HC L2: COILCRAFT, DO1608C-103 L4: COILCRAFT, DO1608C-104 C2, C3: 22F, 6.3V, MURATA GRM31CR70J226KE19 C5: 47F, 6.3V, PANASONIC 6SVP47M C7: 2.2F, 100V, MURATA GRM32ER72A225KA35 T1: WURTH, 750313082 OR PCA EPC3409G Q1-Q9: PSMN075-100MSE T2: PCA EPA4271GE OR PULSE PE-68386NL 25.5W (Type 2) PoE+ Power Supply in Flyback Mode with 5V, 4.7A Output 10k BAT46WS 15 MMBT3904 4276 TA03 1F -VOUT VOUT 5V AT 4.7A TO MICROPROCESSOR MMBT3906 2.2nF C5 47F PSMN2R4-30MLD C2, C3 22F||22F L1 180nH LT4276 Typical Applications 4276fa 17 GND VPORT PTVS58VP1UTP 8.2 10nF 100V 3.3k Q1 EFFICIENCY (%) 18 + For more information www.linear.com/LT4276 76 78 80 82 84 86 88 90 92 94 0.47F 107k 64.9 80.6 1 SG ISEN- ISEN+ VCC FFSDLY PG 13k ROSC ITHB LT4276A 10F 10V BAV19WS VCC GND FB31 RCLASS RCLASS++ SFST T2P 20 FMMT723 L4 100H VIN SWVCC C7 2.2F (x2) 2 3 4 4276 TA04a 5 6 7 8 9 10 11 12 13 LOAD CURRENT (A) VPORT = 41V VPORT = 50V VPORT = 57V Efficiency vs Load Current 0.1F 100V VPORT HSGATE HSSRC 22F 100V 20m 1/4W OPTO 2.2nF 2kV 4 1.2 0.10 4.80 4.85 4.90 4.95 5.00 4276 TA04b 5 6 7 8 9 10 11 12 13 LOAD CURRENT (A) 3.3 38 12 tSFST (ms) CSFST (F) 4276 TA04 3.8 3 10.0k 10nF TO MICROPROCESSOR ZR431 10.0k L1 2.2H C5 100F (x2) + +VOUT +5V AT C8 13A 100F 6HVA100M L1: COILCRAFT, XAL-1010-222ME L2: WURTH, 744314490 L4: COILCRAFT, DO1608C-104 C5, 100F, 6.3V, SUNCON 6HVA100M C7: 2.2F, 100V, MURATA GRM32ER72A225KA35L C8: 100F, 6.3V, SUNCON 6HVA100M T1: WURTH, 750313095 Q1: PSMN040-100MSE 18V CMHZ5248B 1.0 2 240 4.7n 33nF +VOUT 0.1F 18V CMHZ5248B BSC054N04NS 5.05 VPORT = 41V VPORT = 50V VPORT = 57V 10k 330 1k 0.1F 8.2V CMHZ4694 MMBT3904 10 5 CMMSH1-40L 0.33 1 10 CMMSH1-40L BSC054N04NS CMMSH1-40L 5.10 5.15 5.20 750 10nF 250V * M0C207M VCC 100 1206 100nF 250V T1 VOUT vs Load Current 100pF 10k FDMC2523P CMMSH1-40L 100k 0.1F BAT54WS BSC190N12NS3 * 70W LTPoE++ Power Supply in Forward Mode with 5V, 13A Output VOUT (V) L2 4.9H LT4276 Typical Applications 4276fa SPARE PAIRS 8 5 7 4 6 2 3 T2 BG45 TG45 IN78 IN45 IN36 IN12 TG12 BG12 Q5 Q4 For more information www.linear.com/LT4276 VCC 47nF 100V 47nF 100V PTVS58VP1UTP 8.2 10nF 100V 3.3k LT4276A 4276 TA05a 76 0.7 1.4 2.1 2.8 3.5 4.2 4.9 5.6 6.3 7.0 LOAD CURRENT (A) 78 100pF* 100pF CMMSH1-40L 100k 10k FDMC2523P 15m 1/4W 750 33nF 250V VPORT = 41V VPORT = 50V VPORT = 57V OPTO 2.2nF 2kV M0C207M VCC 100 1206 0.22F 250V VOUT vs Load Current 1F 107k 0.1F BAT54WS * CMMSH1-60 * T1 4276 TA05b 10 10k 820 10.0k 38.3k +VOUT 0.1F CMMSH1-100 330pF BSC123N08S3 7.5V CMHZ5236B 5.1k 100pF 1.5 4.9 15 0.33 1.0 48 tSFST (ms) 0.10 4276 TA05 CSFST (F) 3.3 FMMT624 +VOUT CMMSH1-100 L1: COILCRAFT, XAL-1010-822ME L2: WURTH, 744314650 L4: COILCRAFT, DO1608C-104 C5, 100F, 6.3V, TDK C3225X5R0J107M C7: 2.2F, 100V, MURATA GRM32ER72A225KA35L C8: 100F, 16V, SUNCON 16HVA100M T1: PCA EPC3577G-LF T2: WURTH, 749022016 Q1: PSMN040-100MSE Q2-Q9: PSMN075-100MSE FMMT624 +VOUT 100pF 7.5V CMHZ5236B 5.1k TO MICROPROCESSOR ZR431 100pF 6.8nF 20k 13k 7.5 820pF 0.1F 13V CMHZ4700 MMBT3904 11.5 0.7 1.4 2.1 2.8 3.5 4.2 4.9 5.6 6.3 7.0 LOAD CURRENT (A) 11.6 11.7 11.9 12.0 12.1 12.2 12.3 12.4 12.5 64.9 11.8 76.8 ITHB SG ISEN- ISEN+ BSC190N12NS3 29.4k VCC VCC FFSDLY PG SFST ROSC 10F BAV19WS 10V L4 100H 80 VPORT = 41V VPORT = 50V VPORT = 57V 20 FMMT723 VIN SWVCC C7 2.2F (x2) GND FB31 RCLASS RCLASS++ T2P VPORT HSGATE HSSRC 22F 100V L2 6.5H 82 84 86 88 90 92 94 EN OUTN TG78 BG78 EN OUTP BG36 TG36 + Efficiency vs Load Current Q9 Q8 96 Q7 Q6 LT4321 Q3 Q2 Q1 VOUT (V) DATA PAIRS 1 EFFICIENCY (%) 90W LTPoE++ Power Supply in Forward Mode with 12V, 7A Output BSC123N08S3 22F 16V (x2) L1 8.2H +VOUT +12V AT 7A 100F 16V 16HVA100M LT4276 Typical Applications 4276fa 19 SPARE PAIRS 8 5 7 4 6 2 3 DATA PAIRS 1 BG45 TG45 IN78 IN45 IN36 IN12 TG12 BG12 Q5 Q4 Q7 Q9 Q6 Q8 LT4321 Q3 Q2 For more information www.linear.com/LT4276 47nF 100V PTVS58VP1UTP 8.2 10nF 100V LT4276A BAV19WS FMMT723 20 51k 220pF 107k 4276 TA06a 4276 TA06b 4.85 VPORT = 50V VPORT = 57V 4.80 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 LOAD CURRENT (A) 20k 3.3nF 80 VPORT = 50V VPORT = 57V 78 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 LOAD CURRENT (A) Output Regulation vs Load Current 0.1F 7.50k 4.90 4.95 5.00 5.05 5.10 5.15 5.20 35.7 ITHB T2P SG ISEN- ISEN+ 100 * * T2 OPTO 2.2nF 2KV * * 5.1 1/4W 1nF T1 * 2.2nF 2kV 40m 1/4W 1F BSZ900N20 NS3G 100pF 100V 80 1/4W BAT54WS 2.00k 10F 10V VCC FB31 PG 5.90k L4 100H GND RCLASS++ FFSDLY SFST RLDCMP ROSC VPORT VIN SWVCC C7 2.2F HSSRC HSGATE 47F 100V 10F 100V L1: COILCRAFT, DO1813P-181HC L2: COILCRAFT, DO1608C-103 L4: COILCRAFT, DO1608C-104 C2, C3: 47F, 6.3V, GRM31CR60J476ME19L C5: 47F, 6.3V, PANASONIC 6SVP47M C7: 2.2F, 100V, MURATA GRM32ER72A225KA35L T1: WURTH, 750314783 OR PCA EPC3586G Q1-Q9: PSMN075-100MSE T2: PCA EPA4271GE OR PULSE PE-68386NL 82 84 86 88 90 92 94 24V 3.3k + Efficiency vs Load Current EN OUTN TG78 BG78 EN OUTP BG36 TG36 Q1 L2 10H VOUT (V) 20 EFFICIENCY (%) 38.7W LTPoE++ Power Supply in Flyback Mode with 5V, 7A Output 10k BAT46WS 15 MMBT3904 4276 TA06 1F -VOUT VOUT 5V AT 7A TO MICROPROCESSOR MMBT3906 2.2nF C5 47F PSMN2R4-30MLD C2, C3 47F||47F L1 180nH LT4276 Typical Applications 4276fa SPARE PAIRS 8 5 7 4 6 2 3 DATA PAIRS 1 BG45 TG45 IN78 IN45 IN36 IN12 TG12 BG12 MMSD4148 x3 VAUX 9V TO 57VDC OR 24VAC Q5 Q4 Q7 Q9 Q6 Q8 LT4321 Q3 Q2 For more information www.linear.com/LT4276 47nF 100V OUTN 1F 8.2 + VAUX = 9V VAUX = 24V VAUX = 42.5V VAUX = 57V 47nF 100V 4276 TA08a 931k 158k 10F 100V L2 8.2H L3 2.2H 63V + 680F 68nF 0.1F 100V 3.3k Q1 PTVS58VP1UTP LT4320 OUTP Efficiency vs Load Current 24V BG1 BG2 IN2 IN1 TG1 70 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 LOAD CURRENT (A) 72 74 76 78 80 82 84 86 88 90 92 94 EN OUTN TG78 BG78 EN OUTP BG36 TG36 EFFICIENCY (%) TG2 VIN SWVCC LT4276B 22F 10V PMEG10010ELR L4 FMMT723 22H 1 35.7 220pF 107k VAUX = 9V VAUX = 24V VAUX = 42.5V VAUX = 57V 43k 4.7nF 100 4276 TA08b T1 * 220pF * * 2.2nF 2kV T2 * OPTO 2.2nF 2KV * 15m 1/4W 82||82 1/4W 1F FDMC86160 100pF 100V 62 1/4W BAT54WS 2.00k 4.75k 11.5 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 LOAD CURRENT (A) 11.6 11.7 11.8 11.9 12.0 12.1 12.2 12.3 12.4 12.5 51k ITHB T2P SG ISEN- ISEN+ VCC FB31 PG Output Regulation vs Load Current 0.1F 9.31k GND RCLASS FFSDLY SFST RLDCMP ROSC VPORT AUX HSSRC HSGATE C7, C8 3.3F L1: COILCRAFT, DO1813P-561ML L2: WURTH, 7443330820 L3: MURATA, LQM31PN2R2M00L L4: COILCRAFT, DO1813H-223 C2, C3: 10F, 16V, MURATA GRM31CR61C106KA88 C5: 33F, 20V, KEMET, T494V336M020AS C7, C8: 3.3F, 100V, TDK C3225X7S2A335M T1: PCA EPC3601G OR WURTH 750315422 Q1: PSMN075-100MSE Q1-Q9:PSMN075-100MSE T2: PCA EPA4271GE OR PULSE PE-68386NL 10k BAT46WS 15 CMLT3820G 4276 TA08 1F -VOUT VOUT 12V AT 1.9A TO MICROPROCESSOR CMLT7820G 2.2nF C5 33F BSZ900NF20NS3 C2, C3 10F||10F L1 560nH 25.5W (Type 2) PoE+ and 9V-57V Auxiliary Input Power Supply in Flyback Mode with 12V, 1.9A Output VOUT (V) BSZ110N06NS3 x4 LT4276 Typical Applications 4276fa 21 SPARE PAIRS 8 5 7 4 6 2 3 DATA PAIRS 1 BG45 TG45 IN78 IN45 IN36 IN12 TG12 BG12 Q5 Q4 Q7 Q9 Q6 Q8 LT4321 Q3 Q2 For more information www.linear.com/LT4276 47nF 100V VPORT = 42.5V VPORT = 50V VPORT = 57V 4276 TA09a 107k 470pF ITHB 8.25k 4.7nF 100 BAT54WS 4276 TA09b * * 1F T2 * 5.1 1/4W OPTO 2.2nF 2KV * * 1nF T1 2.2nF 2kV 40m 1/4W 100pF 100V 100 1/4W BSZ900N20NS3 VPORT = 42.5V VPORT = 50V VPORT = 57V 2k 6.49k 3.1 0.7 1.4 2.1 2.8 3.5 4.2 4.9 5.6 6.3 7.0 LOAD CURRENT (A) 3.2 3.3 3.4 3.5 0.1F ROSC T2P SG ISEN- ISEN+ VCC FB31 PG Output Regulation vs Load Current 6.81k SFST LT4276B 3.6 L4 100H 10F BAV19WS 10V FMMT723 20 FFSDLY 35.7 GND RCLASS VPORT VIN SWVCC C7 2.2F HSSRC HSGATE 47nF 100V 10F 100V PTVS58VP1UTP 8.2 10nF 100V Efficiency vs Load Current 24V 3.3k + 72 0.7 1.4 2.1 2.8 3.5 4.2 4.9 5.6 6.3 7.0 LOAD CURRENT (A) 74 76 78 80 82 84 86 88 90 92 EN OUTN TG78 BG78 EN OUTP BG36 TG36 Q1 L2 10H L1: COILCRAFT, DO1813P-181HC L2: COILCRAFT, DO1608C-103 L4: COILCRAFT, DO1608C-104 C2, C3: 22F, 6.3V, MURATA GRM31CR70J226KE19 C5: 68F, 4V, 4SVPA68MAA C7: 2.2F, 100V, MURATA GRM32ER72A225KA35 T1: WURTH, 750310743 OR PCA EPC3408G Q1-Q9: PSMN075-100MSE T2: PCA EPA4271GE OR PULSE PE-68386NL VOUT (V) 22 EFFICIENCY (%) 25.5W (Type 2) PoE+ Power Supply in Flyback Mode with 3.3V, 6.8A Output 10k BAT46WS 15 MMBT3904 4276 TA09 1F -VOUT VOUT 3.3V AT 6.8A TO MICROPROCESSOR MMBT3906 2.2nF 47 C5 68F PSMN2R4-30MLD B0540WS C2, C3 22F||22F L1 180nH LT4276 Typical Applications 4276fa SPARE PAIRS 8 5 7 4 6 2 3 DATA PAIRS 1 BG45 TG45 IN78 IN45 IN36 IN12 TG12 BG12 Q5 Q4 Q7 Q9 Q6 Q8 LT4321 Q3 For more information www.linear.com/LT4276 47nF 100V PTVS58VP1UTP 8.2 10nF 100V 4276 TA10a 74 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 LOAD CURRENT (A) 3.3nF 160k VPORT = 42.5V VPORT = 50V VPORT = 57V VOUT vs Load Current 10pF 107k 4276 TA10b 100 BAT54WS 23.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 LOAD CURRENT (A) 23.2 23.4 76 23.6 23.8 24.0 24.2 24.4 24.6 24.8 25.0 0.47F 24k ITHB T2P SG ISEN- ISEN+ 100 1/4W 47pF 100V * 150pF T1 * OPTO 2.2nF 2KV * T2 C5 22F 10k 4276 TA10 0.1F -VOUT VOUT 24V AT 1A TO MICROPROCESSOR BAT46WS 15 MMBT3904 BSZ12DN20NS3 C2, C3 4.7F 50V MMBT3906 2.2nF 120||120 1/4W * * 2.2nF 2kV 40m 1/4W 1F BSZ520N15NS3G 2.00k 10F 10V VCC FB31 PG 6.49k L4 100H SFST RLDCMP ROSC LT4276B BAV19WS 5.23k 78 VPORT = 42.5V VPORT = 50V VPORT = 57V 20 FMMT723 FFSDLY 35.7 GND RCLASS VPORT VIN SWVCC C7 2.2F HSSRC HSGATE 47nF 100V 10F 100V Efficiency vs Load Current 24V 3.3k + 80 82 84 86 88 90 92 94 EN OUTN TG78 BG78 EN OUTP BG36 TG36 Q1 L2 10H L2: COILCRAFT, DO1608C-103 L4: COILCRAFT, DO1608C-104 C2: 4.7F, 50V, MURATA GRM31CR71H475M012 C5: 22F, 35V, PANASONIC EEH-ZA1V220R C7: 2.2F, 100V, MURATA GRM32ER72A225KA35 T1: WURTH, 750314782 OR PCA EPC3603G Q1-Q9: PSMN075-100MSE T2: PCA EPA4271GE OR PULSE PE-68386NL VOUT (V) Q2 EFFICIENCY (%) 25.5W (Type 2) PoE+ Power Supply in Flyback Mode with 24V, 1A Output LT4276 Typical Applications 4276fa 23 LT4276 Package Description Please refer to http://www.linear.com/product/LT4276#packaging for the most recent package drawings. UFD Package 28-Lead Plastic QFN (4mm x 5mm) (Reference LTC DWG # 05-08-1712 Rev B) 0.70 0.05 4.50 0.05 3.10 0.05 2.50 REF 2.65 0.05 3.65 0.05 PACKAGE OUTLINE 0.25 0.05 0.50 BSC 3.50 REF 4.10 0.05 5.50 0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 0.10 (2 SIDES) 0.75 0.05 R = 0.05 TYP PIN 1 NOTCH R = 0.20 OR 0.35 x 45 CHAMFER 2.50 REF R = 0.115 TYP 27 28 0.40 0.10 PIN 1 TOP MARK (NOTE 6) 1 2 5.00 0.10 (2 SIDES) 3.50 REF 3.65 0.10 2.65 0.10 (UFD28) QFN 0506 REV B 0.200 REF 0.00 - 0.05 0.25 0.05 0.50 BSC BOTTOM VIEW--EXPOSED PAD NOTE: 1. DRAWING PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220 VARIATION (WXXX-X). 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 24 4276fa For more information www.linear.com/LT4276 LT4276 Revision History REV DATE DESCRIPTION A 12/15 Changed diode type of diode between SWVCC and VCC from Schottky to regular (BAV19WS) on all applicable schematics. PAGE NUMBER Added additional conditions to VAUXT and IAUXH parameters. Revised graph: PG Delay Time vs Temperature in Flyback Mode. Added T2 transformer part number recommendation to all flyback schematics. Updated parts list for 25.5W (12V/1.9A) flyback schematic. 1, 10, 16-20, 22, 23 3 5 16, 17, 19-23, 26 21 4276fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. For more information www.linear.com/LT4276 25 LT4276 Typical Application 25.5W (Type 2) PoE+ Power Supply in Flyback Mode with 12V, 1.9A Output C5: 22F, 16V, PANASONIC 16SVP22M C7: 2.2F, 100V, MURATA GRM32ER72A225KA35 T1: WURTH, 750310742 OR PCA EPC3410G Q1-Q9: PSMN075-100MSE T2: PCA EPA4271GE OR PULSE PE-68386NL L1: COILCRAFT, DO1813P-181HC L2: COILCRAFT, DO1608C-103 L4: COILCRAFT, DO1608C-104 C2: 10F, 16V, MURATA GRM31CR61C106KA88 L2 10H Q1 + DATA PAIRS Q2 1 Q4 2 3 Q5 SPARE PAIRS HSSRC HSGATE OUTP IN12 IN36 IN45 4 LT4321 5 7 47nF 100V 24V 8 Q7 Q8 Q9 C5 22F T1 -VOUT FDMC86160 470pF 13 1/4W MMBT3906 SG 35.7 SFST ROSC 5.23k 2.2nF T2 1F ITHB 107k MMBT3904 15 100 T2P 47nF 100V 1F 40m 1/4W ISEN- FFSDLY VOUT 12V AT 1.9A BSZ520N15NS3G LT4276B VPORT PTVS58VP1UTP * 47pF 630V 150V 1/4W BAT54WS GND RCLASS Q6 VCC FB31 PG C2 10F ISEN+ EN OUTN TG78 BG78 BG45 TG45 VIN SWVCC 10nF 100V 8.2 IN78 2.00k 3.3k EN 6 6.49k 10F BAV19WS 10V BG36 TG36 L1 180nH * L4 FMMT723 100H Q3 TG12 BG12 * 20 C7 2.2F 10F 100V 2.2nF 2kV * * 10k BAT46WS 3.3nF 0.1F 220pF 26.1k 10k 2.2nF VOUT 2KV 47k TO MICROPROCESSOR MOC207M 4276 TA11 Efficiency vs Load Current Output Regulation vs Load Current 92 12.5 90 12.4 88 12.3 12.2 84 VOUT (V) EFFICIENCY (%) 86 82 80 78 12.1 12.0 11.9 11.8 76 VPORT = 42.5V VPORT = 50V VPORT = 57V 74 72 70 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 LOAD CURRENT (A) 4276 TA11a 11.7 11.6 VPORT = 42.5V VPORT = 50V VPORT = 57V 11.5 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 LOAD CURRENT (A) 4276 TA11b Related Parts PART NUMBER DESCRIPTION COMMENTS LTC4267/ LTC4267-1/ LTC4267-3 LTC4269-1 IEEE 802.3af PD Interface With Integrated Internal 100V, 400mA Switch, Programmable Class, 200/300kHz Constant Frequency Switching Regulator PWM IEEE 802.3af PD Interface With Integrated Flyback Switching Regulator LTC4269-2 IEEE 802.3af PD Interface With Integrated Forward Switching Regulator LT4275A/B/C LTPoE++/PoE+/PoE PD Controller LTC4278 IEEE 802.3af PD Interface With Integrated Flyback Switching Regulator LTC4290/LTC4271 8-Port PoE/PoE+/LTPoE++ PSE Controller LT4320/LT4320-1 Ideal Diode Bridge Controller LT4321 PoE Ideal Diode Bridge Controller 2-Event Classification, Programmable Class, Synchronous No-Opto Flyback Controller, 50kHz to 250kHz, Aux Support 2-Event Classification, Programmable Class, Synchronous Forward Controller, 100kHz to 500kHz, Aux Support External Switch, LTPoE++ Support 2-Event Classification, Programmable Class, Synchronous No-Opto Flyback Controller, 50kHz to 250kHz, 12V Aux Support Transformer Isolation, Supports IEEE 802.3af, IEEE 802.3at and LTPoE++ PDs 9V-72V ,DC to 600Hz Input. Controls 4-NMOSFETs, Voltage Rectification without Diode Drops Controls 8-NMOSFETs for IEEE-required PD Voltage Rectification without Diode Drops 26 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 For more information www.linear.com/LT4276 (408) 432-1900 FAX: (408) 434-0507 www.linear.com/LT4276 4276fa LT 1215 REV A * PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2015