LTC4266

FEATURES n n n LTC4266 Quad IEEE 802.3at Power over Ethernet Controller DESCRIPTION The LTC®4266 is a quad PSE controller designed for use in IEEE 802.3 Type 1 and Type 2 (high power) compliant Power over Ethernet systems. External power MOSFETs enhance system reliability and minimize channel resistance, cutting power dissipation and eliminating the need for heatsinks even at Type 2 power levels. External power components also allow use at very high power levels while remaining otherwise compatible with the IEEE standard. 80V-rated port pins provide robust protection against external faults. The LTC4266 includes advanced power management features, including current and voltage readback and programmable ICUT and ILIM thresholds. Available C libraries simplify power-management software development; an optional AUTO pin mode provides fully IEEE-compliant standalone operation with no software required. Proprietary 4-point PD detection circuitry minimizes false PD detection while supporting legacy phone operation. Midspan operation is supported with built-in 2-event classification and backoff timing. Host communication is via a 1MHz I2C serial interface. The LTC4266 is available in a 5mm × 7mm QFN package that significantly reduces board space compared with competing solutions. A legacy-compatible 36-pin SSOP package is also available. n n n n n n n n Four Independent PSE Channels Compliant with IEEE 802.3at Type 1 and 2 0.34Ω Total Channel Resistance 130mW/Port at 600mA Advanced Power Management 8-Bit Programmable Current Limit (ILIM) 7-Bit Programmable Overload Currents (ICUT) Fast Shutdown of Preselected Ports 14.5-Bit Port Current/Voltage Monitoring 2-Event Classification Very High Reliability 4-Point PD Detection: 2-Point Forced Voltage 2-Point Forced Current High Capacitance Legacy Device Detection LTC4259A-1 and LTC4258 Pin and SW Compatible 1MHz I2C Compatible Serial Control Interface Midspan Backoff Timer Supports Proprietary Power Levels Above 25W Available in 38-Pin 5mm × 7mm QFN and 36-Pin SSOP Packages APPLICATIONS n n High Power PSE Switches/Routers High Power PSE Midspans L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION Complete 4-Port Ethernet High Power Source 3.3V 0.1µF INT SHDN1 SHDN2 SHDN3 SHDN4 AUTO MSD RESET MID VDD SCL SDAIN SDAOUT AD0 LTC4266 AD1 AD2 AD3 DGND AGND VEE SENSE1 GATE1 OUT1 SENSE2 GATE2 OUT2 SENSE3 GATE3 OUT3 SENSE4 GATE4 OUT4 0.22µF 100V ×4 S1B ×4 S1B ×4 –50V –50V SMAJ58A 1µF PORT1 PORT2 PORT3 4266 TA01 PORT4 4266fb 1 LTC4266 ABSOLUTE MAXIMUM RATINGS Supply Voltages (Note 1) AGND – VEE ........................................... –0.3V to 80V DGND – VEE ........................................... –0.3V to 80V VDD – DGND ......................................... –0.3V to 5.5V Digital Pins SCL, SDAIN, SDAOUT, INT, SHDNn, MSD, ADn, RESET, AUTO, MID........... DGND –0.3V to VDD + 0.3V Analog Pins GATEn, SENSEn, OUTn .......... VEE – 0.3V to VEE + 80V Operating Temperature Range LTC4266C ................................................ 0°C to 70°C LTC4266I ............................................. –40°C to 85°C Junction Temperature (Note 2) ............................. 125°C Storage Temperature Range .................. –65°C to 150°C Lead Temperature (Soldering, 10 sec)................... 300°C PIN CONFIGURATION TOP VIEW RESET MID INT SCL SDAOUT SDAIN AD3 AD2 AD1 1 2 3 4 5 6 7 8 9 36 MSD 34 OUT1 33 GATE1 32 SENSE1 31 OUT2 30 GATE2 29 SENSE2 28 VEE 27 OUT3 26 GATE3 25 SENSE3 24 OUT4 23 GATE4 22 SENSE4 21 AGND 20 SHDN4 19 SHDN3 SDAOUT 1 NC 2 SDAIN 3 AD3 4 AD2 5 AD1 6 AD0 7 DNC 8 NC 9 DGND 10 NC 11 NC 12 13 14 15 16 17 18 19 SHDN1 SHDN2 SHDN3 SHDN4 AGND SENSE4 VDD 39 MID SCL INT 35 AUTO TOP VIEW RESET AUTO OUT1 31 GATE1 30 SENSE1 29 OUT2 28 GATE2 27 SENSE2 26 VEE 25 VEE 24 OUT3 23 GATE3 22 SENSE3 21 OUT4 20 GATE4 MSD 38 37 36 35 34 33 32 AD0 10 NC 11 NC 12 NC 13 NC 14 DGND 15 VDD 16 SHDN1 17 SHDN2 18 GW36 PACKAGE 36-LEAD PLASTIC WIDE SSOP TJMAX = 125°C, θJA = 80°C/W UHF PACKAGE 38-LEAD (5mm × 7mm) PLASTIC QFN EXPOSED PAD IS VEE (PIN 39) MUST BE SOLDERED TO PCB TJMAX = 125°C, θJA = 34°C/W ORDER INFORMATION PACKAGE DESCRIPTION TEMPERATURE RANGE 36-Lead Plastic Wide SSOP 0°C to 70°C 36-Lead Plastic Wide SSOP –40°C to 85°C 0°C to 70°C 38-Lead (5mm × 7mm) Plastic QFN –40°C to 85°C 38-Lead (5mm × 7mm) Plastic QFN 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 non-standard lead based finish parts. 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/ 4266fb LEAD FREE FINISH LTC4266CGW#PBF LTC4266IGW#PBF LTC4266CUHF#PBF LTC4266IUHF#PBF TAPE AND REEL LTC4266CGW#TRPBF LTC4266IGW#TRPBF LTC4266CUHF#TRPBF LTC4266IUHF#TRPBF PART MARKING* LTC4266 LTC4266 4266 4266 2 LTC4266 ELECTRICAL CHARACTERISTICS SYMBOL PARAMETER –48V Supply Voltage The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. AGND – VEE = 54V, AGND = DGND, and VDD – DGND = 3.3V unless otherwise noted. (Notes 3, 4) CONDITIONS AGND – VEE For IEEE Type 1 Complaint Output For IEEE Type 2 Complaint Output VDD – DGND DGND – VEE (AGND – VEE) = 55V (VDD – DGND) = 3.3V First Point, AGND – VOUTn = 9V Second Point, AGND – VOUTn = 3.5V AGND – VOUTn, 5µA ≤ IOUTn ≤ 500µA First Point Second Point AGND – VOUTn = 0V AGND – VOUTn, Open Port AGND – VOUTn, CPORT = 0.15µF l l l l l l l l MIN 45 51 20 3.0 25 TYP MAX 57 57 UNITS V V V V V V mA mA µA µA V V mA V V/µs kΩ kΩ V mA mA mA mA mA mA V mA mA mA mA Undervoltage Lock-out Level VDD VDD Supply Voltage Undervoltage Lock-out Allowable Digital Ground Offset IEE IDD Detection Detection Current – Force Current Detection Voltage – Force Voltage VEE Supply Current VDD Supply Current 25 3.3 2.2 30 4.3 57 –2.4 1.1 220 140 7 3 240 160 8 4 0.8 10.4 15.5 27.5 16.0 53 5.5 13.5 21.5 31.5 45.2 7.5 53 0.4 0.08 8 2 300 2.4 500 61 6.5 14.5 23 33 48 9 61 17 29.7 –5 3 260 180 9 5 0.9 12 0.01 18.5 32 20.5 67 7.5 15.5 24.5 34.9 50.8 10 67 l l l l l l l l l Detection Current Compliance VOC Detection Voltage Compliance Detection Voltage Slew Rate Min. Valid Signature Resistance Max. Valid Signature Resistance Classification VCLASS Classification Voltage Classification Current Compliance Classification Threshold Current AGND – VOUTn, 0mA ≤ ICLASS ≤ 50mA VOUTn = AGND Class 0 – 1 Class 1 – 2 Class 2 – 3 Class 3 – 4 Class 4 – Overcurrent AGND – VOUTn, 0.1mA ≤ ICLASS ≤ 10mA VOUTn = AGND Port Off, VGATEn = VEE + 5V Port Off, VGATEn = VEE + 1V VGATEn = VEE + 5V VGATEn – VEE, IGATEn = 1µA VOUTn – VEE 0V ≤ (AGND – VOUTn) ≤ 5V l l l l l l l l l VMARK Gate Driver Classification Mark State Voltage Mark State Current Compliance GATE Pin Pull-Down Current GATE Pin Fast Pull-Down Current GATE Pin On Voltage l l 0.12 30 14 2.8 700 l V V kΩ Output Voltage Sense VPG Power Good Threshold Voltage OUT Pin Pull-Up Resistance to AGND l l 4266fb 3 LTC4266 ELECTRICAL CHARACTERISTICS SYMBOL Current Sense VCUT Overcurrent Sense Voltage VSENSEn – VEE, icut12 = icut34 = hpen = 00h hpen = 0Fh, cutn[5:0] ≥ 4 (Note 12) cutrng = 0 cutrng = 1 Class 0, Class 3 Class 1 Class 2 Class 4 VSENSEn – VEE, dblpwr = hpen = 00h VEE = 55V (Note 12) VEE < VOUT < AGND – 29V AGND – VOUT = 0V hpen = 0Fh, limn = C0h, VEE = 55V VOUT – VEE = 0V to 10V VEE + 23V < VOUT < AGND – 29V AGND – VOUT = 0V VOUT – VEE = 0V to 10V, VEE = 55V Class 0 to Class 3 Class 4 VSENSEn – VEE, rdis = 0 VSENSEn – VEE, rdis = 1 VSENSEn – VEE – VLIM, rdis = 0 VSENSEn – VEE – VLIM, rdis = 1 No missing codes, fast_iv = 0 VSENSEn – VEE (Note 7) No missing codes, fast_iv = 0 AGND – VOUTn (Note 7) (Note 6) (Note 6) ISDAOUT = 3mA, IINT = 3mA ISDAOUT = 5mA, IINT = 5mA ADn, SHDNn, RESET, MSD AUTO, MID l l l l l l l l l l l The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. AGND – VEE = 54V, AGND = DGND, and VDD – DGND = 3.3V unless otherwise noted. (Notes 3, 4) PARAMETER CONDITIONS MIN 180 9 4.5 90 26 49 152 TYP 188 9.38 4.69 94 28 52 159 MAX 196 9.75 4.88 98 30 55 166 UNITS mV mV/LSB mV/LSB mV mV mV mV Overcurrent Sense in AUTO pin mode VLIM Active Current Limit in 802.3af Compliant Mode l l l l l l l l l l l 204 40 204 100 20 102 204 2.6 1.3 160 75 212 220 100 221 113 50 110 221 4.8 2.41 255 135 mV mV mV mV mV mV mV mV mV mV mV bits µV/LSB dB bits mV/LSB dB VLIM Active Current Limit in High Power Mode 212 106 VLIM VMIN VSC Active Current Limit in AUTO pin mode 106 212 3.8 1.9 200 100 14 30.5 30 14 5.835 30 DC Disconnect Sense Voltage Short-Circuit Sense Port Current ReadBack Resolution LSB Weight 50-60Hz Noise Rejection Port Voltage ReadBack Resolution LSB Weight 50-60Hz noise rejection Digital Interface VILD VIHD Digital Input Low Voltage Digital Input High Voltage Digital Output Low Voltage Internal Pull-Up to VDD Internal Pull-Down to DGND 0.8 2.2 0.4 0.7 50 50 V V V V kΩ kΩ 4266fb 4 LTC4266 ELECTRICAL CHARACTERISTICS SYMBOL tDET tDETDLY tCLE1 tME1 tCLE2 tME2 tCLE3 tPON PARAMETER Detection Time Detection Delay First Class Event Duration First Mark Event Duration Second Class Event Duration Second Mark Event Duration Third Class Event Duration Power On Delay in AUTO pin mode Turn On Rise Time Turn On Ramp Rate Fault Delay Midspan Mode Detection Backoff Power Removal Detection Delay tSTART tLIM, tICUT Timing Characteristics Beginning to End of Detection (Note 7) From PD Connected to Port to Detection Complete (Note 7) (Note 7) (Notes 7, 11) (Note 7) (Note 7) CPORT = 0.6µF (Note 7) From End of Valid Detect to Application of Power to Port (Note 7) (AGND – VOUT): 10% to 90% of (AGND – VEE), CPORT = 0.15µF (Note 7) CPORT = 0.15µF (Note 7) From ICUT Fault to Next Detect Rport = 15.5kΩ (Note 7) From Power Removal After tDIS to Next Detect (Note 7) l l l l l l l l l l l l l l l l l l l l l The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. AGND – VEE = 54V, AGND = DGND, and VDD – DGND = 3.3V unless otherwise noted. (Notes 3, 4) CONDITIONS MIN 270 300 11 6.8 11 19 12 8.6 12 22 0.1 60 15 24 10 1.0 2.3 1.0 52 52 5.8 1.6 320 350 1.1 2.5 1.3 62.5 62.5 6.3 2.7 2.5 66 66 6.7 3.6 380 6.5 6.5 1.5 3 3 4.5 2 3 TYP 290 MAX 310 470 13 10.3 13 UNITS ms ms ms ms ms ms ms ms µs V/µs s s s ms ms % ms ms µs µs s µs µs µs Maximum Current Limit Duration During Port tSTART1 = 0, tSTART0 = 0 (Notes 7, 12) Start-Up Maximum Current Limit Duration After Port Start-Up Maximum Current Limit Duty Cycle tICUT1 = 0, tICUT0 = 0 (Notes 7, 12) (Note 7) tMPS tDIS tMSD tSHDN Maintain Power Signature (MPS) Pulse Width Current Pulse Width to Reset Disconnect Sensitivity Timer (Notes 7, 8) Maintain Power Signature (MPS) Dropout Time Masked Shut Down Delay Port Shut Down Delay I2C Watchdog Timer Duration Minimum Pulse Width for Masked Shut Down Minimum Pulse Width for SHDN Minimum Pulse Width for RESET (Note 7) (Note 7) (Note 7) tconf [1:0] = 00b (Notes 5, 12) (Note 7) (Note 7) l l l 4266fb 5 LTC4266 ELECTRICAL CHARACTERISTICS SYMBOL I2C Timing Clock Frequency t1 t2 t3 t4 t5 t6 t7 t8 tr tf Bus Free Time Start Hold Time SCL Low Time SCL High Time Data Hold Time Data Set-Up Time Start Set-Up Time Stop Set-Up Time SCL, SDAIN Rise Time SCL, SDAIN Fall Time Fault Present to INT Pin Low Stop Condition to INT Pin Low ARA to INT Pin High Time SCL Fall to ACK Low (Note 7) Figure 5 (Notes 7, 9) Figure 5 (Notes 7, 9) Figure 5 (Notes 7, 9) Figure 5 (Notes 7, 9) Figure 5 (Notes 7, 9) Data into chip Data out of chip Figure 5 (Notes 7, 9) Figure 5 (Notes 7, 9) Figure 5 (Notes 7, 9) Figure 5 (Notes 7, 9) Figure 5 (Notes 7, 9) (Notes 7, 9, 10) (Notes 7, 9, 10) (Notes 7, 9) (Notes 7, 9) l l l l l l l l l l l l l l l l The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. AGND – VEE = 54V, AGND = DGND, and VDD – DGND = 3.3V unless otherwise noted. (Notes 3, 4) PARAMETER CONDITIONS MIN TYP MAX 1 480 240 480 240 60 80 240 240 120 60 150 1.5 1.5 120 120 UNITS MHz ns ns ns ns ns ns ns ns ns ns ns ns µs µs ns 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: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 140°C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may impair device reliability. Note 3: All currents into device pins are positive; all currents out of device pins are negative. Note 4: The LTC4266 operates with a negative supply voltage (with respect to ground). To avoid confusion, voltages in this data sheet are referred to in terms of absolute magnitude. Note 5: tDIS is the same as tMPDO defined by IEEE 802.3at. Note 6: The LTC4266 digital interface operates with respect to DGND. All logic levels are measured with respect to DGND. Note 7: Guaranteed by design, not subject to test. Note 8: The IEEE 802.3af specification allows a PD to present its Maintain Power Signature (MPS) on an intermittent basis without being disconnected. In order to stay powered, the PD must present the MPS for tMPS within any tMPDO time window. Note 9: Values measured at VILD(MAX) and VIHD(MIN). Note 10: If fault condition occurs during an I2C transaction, the INT pin will not be pulled down until a stop condition is present on the I2C bus. Note 11: Load Characteristic of the LTC4266 during Mark: 7V < (AGND – VOUTn) < 10V or IOUT < 50µA Note 12: See the LTC4266 Software Programming documentation for information on serial bus usage and device configuration and status registers. 4266fb 6 LTC4266 TYPICAL PERFORMANCE CHARACTERISTICS Power On Sequence in AUTO Pin Mode 10 0 –10 PORT VOLTAGE (V) –20 –30 –40 –50 –60 –70 100ms/DIV 4266 G01 Powering Up into a 180µF Load GND PORT VOLTAGE 20V/DIV VEE PORT CURRENT 200 mA/DIV 0mA GATE VOLTAGE 10V/DIV VEE FOLDBACK VDD = 3.3V VEE = –54V LOAD FULLY CHARGED GND 802.3af Classification in AUTO Pin Mode FORCED CURRENT DETECTION GND FORCED VOLTAGE DETECTION PORT 1 VDD = 3.3V VEE = –54V VEE 802.3af CLASSIFICATION POWER ON –18.4 425mA CURRENT LIMIT PORT VOLTAGE 10V/DIV FET ON VEE 5ms/DIV 4266 G02 PORT 1 VDD = 3.3V VEE = –55V PD IS CLASS 1 5ms/DIV 4266 G03 2-Event Classification in Auto Pin Mode GND PORT CURRENT 20mA/DIV 1ST CLASS EVENT 2ND CLASS EVENT PORT VOLTAGE 10V/DIV PORT 1 VDD = 3.3V VEE = –55V PD IS CLASS 4 40mA Classification Transient Response to 40mA Load Step VDD = 3.3V VEE = –54V CLASSIFICATION VOLTAGE (V) 0 –2 –4 –6 –8 –10 –12 –14 –16 –18 –20 50µs/DIV 4266 G04 4266 G05 Classification Current Compliance VDD = 3.3V VEE = –54V TA = 25°C –17.6 0mA PORT VOLTAGE 1V/DIV VEE 10ms/DIV –20V 0 10 20 30 40 50 60 CLASSIFICATION CURRENT 70 4266 G06 1.8 1.7 IDD SUPPLY CURRENT (mA) 1.6 1.5 1.4 1.3 1.2 1.1 1.0 0.9 0.8 VDD Supply Current vs Voltage –40°C 25°C 85°C 2.4 VEE Supply Current vs Voltage 215 214 213 802.3at ILIM Threshold vs Temperature VDD = 3.3V VEE = –54V RSENSE = 0.25 REG 48h = C0h 860 856 852 IEE SUPPLY CURRENT (mA) 2.3 VLIM (mV) ILIM (mA) 2.2 212 848 2.1 –40°C 25°C 85°C 211 844 2.7 2.9 3.1 3.3 3.5 3.7 3.9 VDD SUPPLY VOLTAGE (V) 4.1 4.3 2.0 –60 –55 –50 –45 –40 –35 –30 –25 –20 VEE SUPPLY VOLTAGE (V) 4266 G08 210 –40 0 40 –80 TEMPERATURE (°C) 840 120 4266 G09 4266 G07 4266fb 7 LTC4266 TYPICAL PERFORMANCE CHARACTERISTICS 802.3af ILIM Threshold vs Temperature 108.00 VDD = 3.3V VEE = –54V RSENSE = 0.25 REG 48h = 80h PORT 1 432 163 162 802.3at ICUT Threshold vs Temperature VDD = 3.3V VEE = –54V RSENSE = 0.25 REG 47h = E2h PORT 1 652 648 107.25 VLIM (mV) 429 VCUT (mV) ILIM (mA) 161 644 ICUT (mA) 106.50 426 160 640 105.75 423 159 158 –40 636 630 120 4266 G11 105.00 –40 0 40 80 TEMPERATURE (°C) 420 120 4266 G10 0 40 80 TEMPERATURE (°C) 802.3af ICUT Threshold vs Temperature 96.00 VDD = 3.3V VEE = –54V RSENSE = 0.25 REG 47h = D4h PORT 1 384 2.0000 DC Disconnect Threshold vs Temperature VDD = 3.3V VEE = –54V RSENSE = 0.25 REG 47h = E2h PORT 1 8.00 95.25 VCUT (mV) 381 VMIN (mV) ICUT (mA) 1.9375 7.75 IMIN (mV) 94.50 378 1.8750 7.50 93.75 375 1.8125 7.25 93.00 –40 0 80 40 TEMPERATURE (°C) 372 120 4266 G12 1.7500 –40 0 80 40 TEMPERATURE (°C) 7.00 120 4266 G13 Current Limit Foldback 900 800 700 600 ILIM (mA) 500 400 300 200 100 0 –54 –45 –36 –18 –27 VOUTn (V) –9 0 4266 G14 ADC Noise Histogram Current Readback in Fast Mode 225 200 175 150 125 100 75 50 25 0 BIN COUNT VLIM (mV) 400 350 300 250 200 150 100 50 0 191 192 193 194 ADC OUTPUT 195 196 4266 G15 ADC Integral Nonlinearity Current Readback in Fast Mode 1.0 ADC INTEGRAL NONLINEARITY (LSBs) VDD = 3.3V VEE = –54V RSENSE = 0.25 REG 48h = C0h VSENSEn – VEE = 110.4mV 0.5 0 –0.5 –1.0 0 50 100 150 200 250 300 350 400 450 500 CURRENT SENSE RESISTOR INPUT VOLTAGE (mV) 4266 G16 4266fb 8 LTC4266 TYPICAL PERFORMANCE CHARACTERISTICS ADC Noise Histogram Current Readback in Slow Mode 300 250 200 BIN COUNT 150 100 50 0 VSENSEn – VEE = 110.4mV ADC INTEGRAL NONLINEARITY (LSBs) 1.0 ADC Integral Nonlinearity Current Readback in Slow Mode 600 500 0.5 400 0 BIN COUNT 300 200 –0.5 100 –1.0 0 ADC Noise Histogram Port Voltage Readback in Fast Mode AGND – VOUTn = 48.3V 6139 6141 6143 ADC OUTPUT 6145 6147 4266 G17 0 50 100 150 200 250 300 350 400 450 500 CURRENT SENSE RESISTOR INPUT VOLTAGE (mV) 4266 G18 260 261 262 263 ADC OUTPUT 264 265 4266 G19 ADC Integral Nonlinearity Voltage Readback in Fast Mode 1.0 ADC INTEGRAL NONLINEARITY (LSBs) 600 500 0.5 400 BIN COUNT 0 300 200 –0.5 100 –1.0 0 ADC Noise Histogram Port Voltage Readback in Slow Mode ADC INTEGRAL NONLINEARITY (LSBs) AGND – VOUTn = 48.3V 1.0 ADC Integral Nonlinearity Voltage Readback in Slow Mode 0.5 0 –0.5 0 10 20 40 30 PORT VOLTAGE (V) 50 60 4266 G20 8532 8533 8534 8535 ADC OUTPUT 8536 4266 G21 –1.0 0 10 20 40 30 PORT VOLTAGE (V) 50 60 4266 G22 INT and SDAOUT Pull Down Voltage vs Load Current 3 2.5 PULL DOWN VOLTAGE (V) 2 1.5 1 0.5 0 PORT VOLTAGE 20V/DIV VEE GATE VOLTAGE 10V/DIV VEE PORT CURRENT 500mA/DIV 0mA 0 5 10 15 20 25 30 LOAD CURRENT (mA) 35 40 GND MOSFET Gate Drive With Fast Pull Down VDD = 3.3V VEE = –54V FAST PULL DOWN 50 FAULT APPLIED CURRENT LIMIT 50 FAULT REMOVED 100µs/DIV 4266 G24 4266 G23 4266fb 9 LTC4266 TEST TIMING DIAGRAMS tDET FORCED-CURRENT VPORTn 0V VOC FORCEDVOLTAGE VMARK VCLASS tCLE1 tCLE2 PD CONNECTED tCLE3 CLASSIFICATION tME1 tME2 15.5V 20.5V tDETDLY INT tPON VEE 4266 F01 Figure 1. Detect, Class and Turn-On Timing in AUTO Pin or Semi-Auto Modes VLIM VSENSEn TO VEE 0V INT VCUT tSTART, tICUT VSENSEn TO VEE VMIN INT tMPS 4266 F02 tDIS 4266 F03 Figure 2. Current Limit Timing Figure 3. DC Disconnect Timing t3 VGATEn t4 tMSD tSHDN VEE SCL t2 SDA 4266 F04 tr tf MSD or SHDNn t5 t6 t7 t8 4266 F05 t1 Figure 4. Shut Down Delay Timing Figure 5. I2C Interface Timing 4266fb 10 LTC4266 I2C TIMING DIAGRAMS SCL SDA 0 1 0 AD3 AD2 AD1 AD0 R/W ACK A7 A6 A5 A4 A3 A2 A1 A0 ACK D7 D6 D5 D4 D3 D2 D1 D0 ACK START BY MASTER FRAME 1 SERIAL BUS ADDRESS BYTE ACK BY SLAVE ACK BY SLAVE FRAME 3 DATA BYTE ACK BY SLAVE STOP BY MASTER FRAME 2 REGISTER ADDRESS BYTE 4266 F06 Figure 6. Writing to a Register SCL SDA 0 1 0 AD3 AD2 AD1 AD0 R/W ACK A7 A6 A5 A4 A3 A2 A1 A0 ACK 0 1 0 AD3 AD2 AD1 AD0 R/W ACK D7 D6 D5 D4 D3 D2 D1 D0 ACK START BY MASTER FRAME 1 SERIAL BUS ADDRESS BYTE ACK BY SLAVE ACK BY SLAVE FRAME 2 REGISTER ADDRESS BYTE REPEATED START BY MASTER ACK BY SLAVE FRAME 2 DATA BYTE NO ACK BY MASTER STOP BY MASTER FRAME 1 SERIAL BUS ADDRESS BYTE 4266 F07 Figure 7. Reading from a Register SCL SDA 0 1 0 AD3 AD2 AD1 AD0 R/W ACK D7 D6 D5 D4 D3 D2 D1 D0 ACK START BY MASTER FRAME 1 SERIAL BUS ADDRESS BYTE ACK BY SLAVE FRAME 2 DATA BYTE NO ACK BY MASTER STOP BY MASTER 4266 F08 Figure 8. Reading the Interrupt Register (Short Form) SCL SDA 0 0 0 1 1 0 0 R/W ACK 0 1 0 AD3 AD2 AD1 AD0 1 ACK START BY MASTER FRAME 1 ALERT RESPONSE ADDRESS BYTE ACK BY SLAVE NO ACK BY MASTER STOP BY MASTER 4266 F09 FRAME 2 SERIAL BUS ADDRESS BYTE Figure 9. Reading from Alert Response Address 4266fb 11 LTC4266 PIN FUNCTIONS RESET: Chip Reset, Active Low. When the RESET pin is low, the LTC4266 is held inactive with all ports off and all internal registers reset to their power-up states. When RESET is pulled high, the LTC4266 begins normal operation. RESET can be connected to an external capacitor or RC network to provide a power turn-on delay. Internal filtering of the RESET pin prevents glitches less than 1µs wide from resetting the LTC4266. Internally pulled up to VDD. MID: Midspan Mode Input. When high, the LTC4266 acts as a midspan device. Internally pulled down to DGND. INT: Interrupt Output, Open Drain. INT will pull low when any one of several events occur in the LTC4266. It will return to a high impedance state when bits 6 or 7 are set in the Reset PB register (1Ah). The INT signal can be used to generate an interrupt to the host processor, eliminating the need for continuous software polling. Individual INT events can be disabled using the Int Mask register (01h). See LTC4266 Software Programming documentation for more information. The INT pin is only updated between I2C transactions. SCL: Serial Clock Input. High impedance clock input for the I2C serial interface bus. SCL must be tied high if not used. SDAOUT: Serial Data Output, Open Drain Data Output for the I2C Serial Interface Bus. The LTC4266 uses two pins to implement the bidirectional SDA function to simplify optoisolation of the I2C bus. To implement a standard bidirectional SDA pin, tie SDAOUT and SDAIN together. SDAOUT should be grounded or left floating if not used. See Applications Information for more information. SDAIN: Serial Data Input. High impedance data input for the I2C serial interface bus. The LTC4266 uses two pins to implement the bidirectional SDA function to simplify optoisolation of the I2C bus. To implement a standard bidirectional SDA pin, tie SDAOUT and SDAIN together. SDAIN must be tied high if not used. See Applications Information for more information. AD3: Address Bit 3. Tie the address pins high or low to set the I2C serial address to which the LTC4266 responds. This address will be 010A3A2A1A0b. Internally pulled up to VDD. AD2: Address Bit 2. See AD3. AD1: Address Bit 1. See AD3. AD0: Address Bit 0. See AD3. NC, DNC: All pins identified with “NC” or “DNC” must be left unconnected. DGND: Digital Ground. DGND is the return for the VDD supply. VDD: Logic Power Supply. Connect to a 3.3V power supply relative to DGND. VDD must be bypassed to DGND near the LTC4266 with at least a 0.1µF capacitor. SHDN1: Shutdown Port 1, Active Low. When pulled low, SHDN1 shuts down port 1, regardless of the state of the internal registers. Pulling SHDN1 low is equivalent to setting the Reset Port 1 bit in the Reset Pushbutton register (1Ah). Internal filtering of the SHDN1 pin prevents glitches less than 1µs wide from reseting the port. Internally pulled up to VDD. SHDN2: Shutdown Port 2, Active Low. See SHDN1. SHDN3: Shutdown Port 3, Active Low. See SHDN1. SHDN4: Shutdown Port 4, Active Low. See SHDN1. AGND: Analog Ground. AGND is the return for the VEE supply. SENSE4: Port 4 Current Sense Input. SENSE4 monitors the external MOSFET current via a 0.5Ω or 0.25Ω sense resistor between SENSE4 and VEE. Whenever the voltage across the sense resistor exceeds the overcurrent detection threshold VCUT, the current limit fault timer counts up. If the voltage across the sense resistor reaches the current limit threshold VLIM, the GATE4 pin voltage is lowered to maintain constant current in the external MOSFET. See Applications Information for further details. If the port is unused, the SENSE4 pin must be tied to VEE. 4266fb 12 LTC4266 PIN FUNCTIONS GATE4: Port 4 Gate Drive. GATE4 should be connected to the gate of the external MOSFET for port 4. When the MOSFET is turned on, the gate voltage is driven to 13V (typ) above VEE. During a current limit condition, the voltage at GATE4 will be reduced to maintain constant current through the external MOSFET. If the fault timer expires, GATE4 is pulled down, turning the MOSFET off and recording a tCUT or tSTART event. If the port is unused, float the GATE4 pin. OUT4: Port 4 Output Voltage Monitor. OUT4 should be connected to the output port. A current limit foldback circuit limits the power dissipation in the external MOSFET by reducing the current limit threshold when the drain-tosource voltage exceeds 10V. The port 4 Power Good bit is set when the voltage from OUT4 to VEE drops below 2.4V (typ). A 500k resistor is connected internally from OUT4 to AGND when the port is idle. If the port is unused, OUT4 pin must be floated. SENSE3: Port 3 Current Sense Input. See SENSE4. GATE3: Port 3 Gate Drive. See GATE4. OUT3: Port 3 Output Voltage Monitor. See OUT4. VEE: Main Supply Input. Connect to a –45V to –57V supply, relative to AGND. SENSE2: Port 2 Current Sense Input. See SENSE4. GATE2: Port 2 Gate Drive. See GATE4. OUT2: Port 2 Output Voltage Monitor. See OUT4. SENSE1: Port 1 Current Sense Input. See SENSE4. GATE1: Port 1 Gate Drive. See GATE 4. OUT1: Port 1 Output Voltage Monitor. See OUT4. AUTO: AUTO Pin Mode Input. AUTO pin mode allows the LTC4266 to detect and power up a PD even if there is no host controller present on the I2C bus. The voltage of the AUTO pin determines the state of the internal registers when the LTC4266 is reset or comes out of VDD UVLO (see the Register map). The states of these register bits can subsequently be changed via the I2C interface. The real-time state of the AUTO pin is read at bit 0 in the Pin Status register (11h). Internally pulled down to DGND. Must be tied locally to either VDD or DGND. MSD: Maskable Shutdown Input. Active low. When pulled low, all ports that have their corresponding mask bit set in the Misc Config register (17h) will be reset, equivalent to pulling the SHDN pin low. Internal filtering of the MSD pin prevents glitches less than 1µs wide from resetting ports. Internally pulled up to VDD. 4266fb 13 LTC4266 OPERATION Overview Power over Ethernet, or PoE, is a standard protocol for sending DC power over copper Ethernet data wiring. The IEEE group that administers the 802.3 Ethernet data standards added PoE powering capability in 2003. This original PoE spec, known as 802.3af, allowed for 48V DC power at up to 13W. This initial spec was widely popular, but 13W was not adequate for some requirements. In 2009, the IEEE released a new standard, known as 802.3at or PoE+, increasing the voltage and current requirements to provide 25W of power. The IEEE standard also defines PoE terminology. A device that provides power to the network is known as a PSE, or power sourcing equipment, while a device that draws power from the network is known as a PD, or powered device. PSEs come in two types: Endpoints (typically network switches or routers), which provide data and power; and Midspans, which provide power but pass through data. Midspans are typically used to add PoE capability to existing non-PoE networks. PDs are typically IP phones, wireless access points, security cameras, and similar devices, but could be nearly anything that runs from 25W or less and includes an RJ45-style network connector. The LTC4266 is a third-generation quad PSE controller that implements four PSE ports in either an endpoint or midspan design. Virtually all necessary circuitry is included to implement a IEEE 802.3at compliant PSE design, requiring only an external power MOSFET and sense resistor per PSE RJ45 4 5 0.22µF 100V X7R Tx 2 3 Rx 6 S1B IRFM120A S1B 7 8 SPARE PAIR 4266 F10 channel; these minimize power loss compared to alternative designs with on-board MOSFETs and increase system reliability in the event a single channel is damaged. PoE Basics Common Ethernet data connections consist of two or four twisted pairs of copper wire (commonly known as CAT-5 cable), transformer-coupled at each end to avoid ground loops. PoE systems take advantage of this coupling arrangement by applying voltage between the center-taps of the data transformers to transmit power from the PSE to the PD without affecting data transmission. Figure 10 shows a high-level PoE system schematic. To avoid damaging legacy data equipment that does not expect to see DC voltage, the PoE spec defines a protocol that determines when the PSE may apply and remove power. Valid PDs are required to have a specific 25k common mode resistance at their input. When such a PD is connected to the cable, the PSE detects this signature resistance and turns on the power. When the PD is later disconnected, the PSE senses the open circuit and turns power off. The PSE also turns off power in the event of a current fault or short circuit. When a PD is detected, the PSE optionally looks for a classification signature that tells the PSE the maximum power the PD will draw. The PSE can use this information to allocate power among several ports, police the current consumption of the PD, or to reject a PD that will draw RJ45 4 5 PD CAT 5 20 MAX ROUNDTRIP 0.05µF MAX GND SPARE PAIR 1 1 Rx DATA PAIR 2 3 Tx DATA PAIR 6 1N4002 ×4 DGND SMAJ58A 3.3V INTERRUPT I2C 1µF 100V X7R –48V VDD INT 1/4 SCL LTC4266 SDAIN SDAOUT VEE AGND SMAJ58A 58V 5µF ≤ CIN ≤ 300µF 0.1µF 1N4002 ×4 GND RCLASS PWRGD LTC4265 DC/DC CONVERTER SENSE GATE OUT + VOUT 0.25 7 8 –48VIN –48VOUT – Figure 10. Power Over Ethernet System Diagram 4266fb 14 LTC4266 OPERATION more power that the PSE has available. The classification step is optional; if a PSE chooses not to classify a PD, it must assume that the PD is a 13W (full 802.3af power) device. New in 802.3at The newer 802.3at standard supersedes 802.3af and brings several new features: • A PD may draw as much as 25.5W. Such PDs (and the PSEs that support them) are known as Type 2. Older 13W 802.3af equipment is classified as Type 1. Type 1 PDs will work with all PSEs; Type 2 PDs may require Type 2 PSEs to work properly. The LTC4266 is designed to work in both Type 1 and Type 2 PSE designs, and also supports non-standard configurations at higher power levels. • The Classification protocol is expanded to allow Type 2 PSEs to detect Type 2 PDs, and to allow Type 2 PDs to determine if they are connected to a Type 2 PSE. Two versions of the new Classification protocol are available: an expanded version of the 802.3af Class Pulse protocol, and an alternate method integrated with the existing LLDP protocol (using the Ethernet data path). The LTC4266 fully supports the new Class Pulse protocol and is also compatible with the LLDP protocol (which is implemented in the data communications layer, not in the PoE circuitry). • Fault protection current levels and timing are adjusted to reduce peak power in the MOSFET during a fault; this allows the new 25.5W power levels to be reached using the same MOSFETs as older 13W designs. BACKWARDS COMPATIBILITY The LTC4266 is designed to be backward compatible with earlier PSE chips in both software and pin functions. Existing systems using either the LTC4258 or LTC4259A (or compatible) devices can be substituted with the LTC4266 without software or PCB layout changes; only minor BOM changes are required to implement a fully compliant 802.3at design. Because of the backwards compatibility features, some of the internal registers are redundant or unused when the LTC4266 is operated as recommended. For more details on usage in compatibility mode, refer to the LTC4258/ LTC4259A device datasheets. Special Compatibility Mode Notes • The LTC4266 can use either 0.5Ω or 0.25Ω sense resistors, while the LTC425x chips always used 0.5Ω. To maintain compatibility, if the AUTO pin is low when the LTC4266 powers up it assumes the sense resistor is 0.5Ω; if it is high at power up, the LTC4266 assumes 0.25Ω. The resistor value setting can be reconfigured at any time after power up. In particular, systems that use 0.25Ω sense resistors and have AUTO tied low must reconfigure the resistor settings after power up. • The LTC4259A included both AC and DC disconnect sensing circuitry, but the LTC4266 has only DC disconnect sensing. For the sake of compatibility, register bits used to enable AC disconnect in the LTC4259A are implemented in the LTC4266, but they simply mirror the bits used for DC disconnect. • The LTC4258 and LTC4259A required 10k resistors between the OUTn pins and the drains of the external MOSFETs. These resistors must be shorted or replaced with zero ohm jumpers when using the LTC4266. • The LTC4258 and LTC4259A included a BYP pin, decoupled to AGND with 0.1µF This pin changes to the MID . pin on the LTC4266. The capacitor should be removed for Endspan applications, or replaced with a zero ohm jumper for Midspan applications. 4266fb 15 LTC4266 APPLICATIONS INFORMATION Operating Modes The LTC4266 includes four independent ports, each of which can operate in one of four modes: manual, semiauto, AUTO pin or shutdown. Table 1. Operating Modes MODE AUTO Pin Reserved Semi-auto Manual Shutdown AUTO PIN OPMD 1 0 0 0 0 11b 11b 10b 01b 00b DETECT/ CLASS POWER-UP AUTOMATIC ICUT/ILIM ASSIGNMENT Yes N/A No No No Reset and the AUTO/MID Pins The initial LTC4266 configuration depends on the state of the AUTO and MID pins during reset. Reset occurs at power-up, or whenever the RESET pin is pulled low or the global Reset All bit is set. Note that the AUTO pin is only sampled when a reset occurs. Changing the state of AUTO or MID after power-up will not change the port behavior of the LTC4266 until a reset occurs. Although typically used with a host controller, the LTC4266 can also be used in a standalone mode with no connection to the serial interface. If there is no host present, the AUTO pin should be tied high so that, at reset, all ports will be configured to operate automatically. Each port will detect and classify repeatedly until a PD is discovered, set ICUT and ILIM according to the classification results, apply power after successful detection, and remove power when a PD is disconnected. Similarly, if the standalone application is a midspan, the MID pin should be tied high to enable correct midspan detection timing. Table 2 shows the ICUT and ILIM values that will be automatically set in AUTO pin mode, based on the discovered class. Table 2. ICUT and ILIM Values in AUTO pin mode CLASS Class 1 Class 2 Class 3 or Class 0 Class 4 ICUT 112mA 206mA 375mA 638mA ILIM 425mA 425mA 425mA 850mA Enabled at Automatically Reset N/A Host Enabled Once Upon Request Disabled N/A Upon Request Upon Request Disabled • In manual mode, the port waits for instructions from the host system before taking any action. It runs a single detection or classification cycle when commanded to by the host, and reports the result in its Port Status register. The host system can command the port to turn on or off the power at any time. This mode should only be used for diagnostic and test purposes. • In semi-auto mode, the port repeatedly attempts to detect and classify any PD attached to it. It reports the status of these attempts back to the host, and waits for a command from the host before turning on power to the port. The host must enable detection (and optionally classification) for the port before detection will start. • AUTO pin mode operates the same as semi-auto mode except that it will automatically turn on the power to the port if detection is successful. In AUTO pin mode, ICUT and ILIM values are set automatically by the LTC4266. The AUTO pin must be high at reset to ensure proper AUTO pin mode operation. • In shutdown mode, the port is disabled and will not detect or power a PD. Regardless of which mode it is in, the LTC4266 will remove power automatically from any port that generates a current limit fault. It will also automatically remove power from any port that generates a disconnect event if disconnect detection is enabled. The host controller may also command the port to remove power at any time. The automatic setting of the ICUT and ILIM values only occurs if the LTC4266 is reset with the AUTO pin high. DETECTION Detection Overview To avoid damaging network devices that were not designed to tolerate DC voltage, a PSE must determine whether the connected device is a real PD before applying power. The IEEE specification requires that a valid PD have a common mode resistance of 25k ±5% at any port voltage below 10V. The PSE must accept resistances that fall between 19k and 26.5k, and it must reject resistances above 33kΩ or below 15k (shaded regions in Figure 11). The PSE may choose to 4266fb 16 LTC4266 APPLICATIONS INFORMATION RESISTANCE 0 PD PSE 150 (NIC) 15k 10k 20k 23.75k 19k 30k 26.25k 26.5k 33k 4266 F11 275 CURRENT (µA) 25k 165 VALID PD SLOPE Figure 11. IEEE 802.3af Signature Resistance Ranges FIRST DETECTION POINT accept or reject resistances in the undefined areas between the must-accept and must-reject ranges. In particular, the PSE must reject standard computer network ports, many of which have 150Ω common mode termination resistors that will be damaged if power is applied to them (the black region at the left of Figure 11). 4-Point Detection The LTC4266 uses a 4-point detection method to discover PDs. False-positive detections are minimized by checking for signature resistance with both forced-current and forced-voltage measurements. Initially, two test currents are forced onto the port (via the OUTn pin) and the resulting voltages are measured. The detection circuitry subtracts the two V-I points to determine the resistive slope while removing offset caused by series diodes or leakage at the port (see Figure 12). If the forced-current detection yields a valid signature resistance, two test voltages are then forced onto the port and the resulting currents are measured and subtracted. Both methods must report valid resistances for the port to report a valid detection. PD signature resistances between 17k and 29k (typically) are detected as valid and reported as Detect Good in the corresponding Port Status register. Values outside this range, including open and short circuits, are also reported. If the port measures less than 1V at the first forced-current test, the detection cycle will abort and Short Circuit will be reported. Table 3 shows the possible detection results. Table 3. Detection Status MEASURED PD SIGNATURE Incomplete or Not Yet Tested 2.7µF 2.4k < RPD < 17k 17k < RPD < 29k >29k >50k Voltage > 10V DETECTION RESULT Detect Status Unknown Short Circuit CPD too High RSIG too Low Detect Good RSIG too High Open Circuit Port Voltage Outside Detect Range SECOND DETECTION POINT 0V-2V OFFSET VOLTAGE 4266 F12 Figure 12. PD Detection Operating Modes The port’s operating mode determines when the LTC4266 runs a detection cycle. In manual mode, the port will idle until the host orders a detect cycle. It will then run detection, report the results, and return to idle to wait for another command. In semi-auto mode, the LTC4266 autonomously polls a port for PDs, but it will not apply power until commanded to do so by the host. The Port Status register is updated at the end of each detection cycle. If a valid signature resistance is detected and classification is enabled, the port will classify the PD and report that result as well. The port will then wait for at least 100ms (or 2 seconds if midspan mode is enabled), and will repeat the detection cycle to ensure that the data in the port status register is up-to-date. If the port is in semi-auto mode and high power operation is enabled, the port will not turn on in response to a power-on command unless the current detect result is Detect Good. Any other detect result will generate a tSTART fault if a power-on command is received. If the port is not in high power mode, it will ignore the detection result and apply power when commanded, maintaining backwards compatibility with the LTC4259A. Behavior in AUTO pin mode is similar to semi-auto; however, after Detect Good is reported and the port is classified (if classification is enabled), it is automatically powered on without further intervention. In AUTO pin mode, the ICUT and ILIM thresholds are automatically set; see the Reset and the AUTO/MID Pins section for more information. 4266fb 17 LTC4266 APPLICATIONS INFORMATION The signature detection circuitry is disabled when the port is initially powered up with the AUTO pin low, in shutdown mode, or when the corresponding detect enable bit is cleared. Detection of Legacy PDs Proprietary PDs that predate the original IEEE 802.3af standard are commonly referred to today as legacy devices. One type of legacy PD uses a large common mode capacitance (>10μF) as the detection signature. Note that PDs in this range of capacitance are defined as invalid, so a PSE that detects legacy PDs is technically noncompliant with the IEEE spec. The LTC4266 can be configured to detect this type of legacy PD. Legacy detection is disabled by default, but can be manually enabled on a per-port basis. When enabled, the port will report detect good when it sees either a valid IEEE PD or a high-capacitance legacy PD. With legacy mode disabled, only valid IEEE PDs will be recognized. CLASSIFICATION 802.3af Classification A PD can optionally present a classification signature to the PSE to indicate the maximum power it will draw while operating. The IEEE specification defines this signature as a constant current draw when the PSE port voltage is in the VCLASS range (between 15.5V and 20.5V), with the current level indicating one of 5 possible PD classes. Figure 14 shows a typical PD load line, starting with the slope of the 25kΩ signature resistor below 10V, then transitioning to the classification signature current (in this case, Class 3) in the VCLASS range. Table 4 shows the possible classification values. Table 4. Classification Values CLASS Class 0 Class 1 Class 2 Class 3 Class 4 RESULT No Class Signature Present; Treat Like Class 3 3W 7W 13W 25.5W (Type 2) 60 50 40 30 20 10 0 PSE LOAD LINE OVER CURRENT 48mA CURRENT (mA) CLASS 4 CLASS 3 33mA 23mA TYPICAL CLASS 3 PD LOAD LINE 0 5 CLASS 2 CLASS 1 CLASS 0 14.5mA 6.5mA 20 25 4266 F13 10 15 VOLTAGE (VCLASS) Figure 13. PD Classification If classification is enabled, the port will classify the PD immediately after a successful detection cycle in semi-auto or AUTO pin modes, or when commanded to in manual mode. It measures the PD classification signature by applying 18V for 12ms (both values typical) to the port via the OUTn pin and measuring the resulting current; it then reports the discovered class in the port status register. If the LTC4266 is in AUTO pin mode, it will additionally use the classification result to set the ICUT and ILIM thresholds. See the Reset and the AUTO/MID Pins section for more information. The classification circuitry is disabled when the port is initially powered up with the AUTO pin low, in shutdown mode, or when the corresponding class enable bit is cleared. 802.3at 2-Event Classification The 802.3at spec defines two methods of classifying a Type 2 PD. One method adds extra fields to the Ethernet LLDP data protocol; although the LTC4266 is compatible with this classification method, it cannot perform classification directly since it doesn’t have access to the data path. LLDP classification requires the PSE to power the PD as a standard 802.3af (Type 1) device. It then waits for the host to perform LLDP communication with the PD and update the PSE port data. The LTC4266 supports changing the ILIM and ICUT levels on the fly, allowing the host to complete LLDP classification. 4266fb 18 LTC4266 APPLICATIONS INFORMATION The second 802.3at classification method, known as 2-event classification or ping-pong, is fully supported by the LTC4266. A Type 2 PD that is requesting more than 13W will indicate Class 4 during normal 802.3af classification. If the LTC4266 sees Class 4, it forces the port to a specified lower voltage (called the mark voltage, typically 9V), pauses briefly, and then re-runs classification to verify the Class 4 reading (Figure 1). It also sets a bit in the High Power Status register to indicate that it ran the second classification cycle. The second cycle alerts the PD that it is connected to a Type 2 PSE which can supply Type 2 power levels. 2-event ping-pong classification is enabled by setting a bit in the port’s High Power Mode register. Note that a pingpong enabled port only runs the second classification cycle when it detects a Class 4 device; if the first cycle returns Class 0 to 3, the port assumes it is connected to a Type 1 PD and does not run the second classification cycle. Invalid Type 2 Class Combinations The 802.3at spec defines a Type 2 PD class signature as two consecutive Class 4 results; a Class 4 followed by a Class 0-3 is not a valid signature. In AUTO pin mode, the LTC4266 will power a detected PD regardless of the classification results, with one exception: if the PD presents an invalid Type 2 signature (Class 4 followed by Class 0 to 3), the LTC4266 will not provide power and will restart the detection process. To aid in diagnosis, the Port Status register will always report the results of the last class pulse, so an invalid Class 4–Class 2 combination would report a second class pulse was run in the High Power Status register (which implies that the first cycle found Class 4), and Class 2 in the Port Status register. POWER CONTROL External MOSFET, Sense R Summary The primary function of the LTC4266 is to control the delivery of power to the PSE port. It does this by controlling the gate drive voltage of an external power MOSFET while monitoring the current via an external sense resistor and the output voltage at the OUT pin. This circuitry serves to couple the raw VEE input supply to the port in a controlled manner that satisfies the PD’s power needs while minimizing power dissipation in the MOSFET and disturbances on the VEE backplane. The LTC4266 is designed to use 0.25Ω sense resistors to minimize power dissipation. It also supports 0.5Ω sense resistors, which are the default when LTC4258/LTC4259A compatibility is desired. Inrush Control Once the command has been given to turn on a port, the LTC4266 ramps up the GATE pin of that port’s external MOSFET in a controlled manner. Under normal power-up circumstances, the MOSFET gate will rise until the port current reaches the inrush current limit level (typically 450mA), at which point the GATE pin will be servoed to maintain the specified IINRUSH current. During this inrush period, a timer (tSTART) runs. When output charging is complete, the port current will fall and the GATE pin will be allowed to continue rising to fully enhance the MOSFET and minimize its on-resistance. The final VGS is nominally 13V. If the tSTART timer expires before the inrush period completes, the port will be turned back off and a tSTART fault reported. Current Limit Each LTC4266 port includes two current limiting thresholds (ICUT and ILIM), each with a corresponding timer (tCUT and tLIM). Setting the ICUT and ILIM thresholds depends on several factors: the class of the PD, the voltage of the main supply (VEE), the type of PSE (1 or 2), the sense resistor (0.5Ω or 0.25Ω), the SOA of the MOSFET, and whether or not the system is required to implement class enforcement. Per the IEEE spec, the LTC4266 will allow the port current to exceed ICUT for a limited period of time before removing power from the port, whereas it will actively control the MOSFET gate drive to keep the port current below ILIM. The port does not take any action to limit the current when only the ICUT threshold is exceeded, but does start the tCUT timer. The tLIM timer starts when the ILIM threshold is exceeded and current limit is active. If the current drops below the ICUT current threshold before its timer expires, the tCUT timer counts back down, but 4266fb 19 LTC4266 APPLICATIONS INFORMATION at 1/16 the rate that it counts up. This allows the current limit circuitry to tolerate intermittent overload signals with duty cycles below about 6%; longer duty cycle overloads will turn the port off. ICUT is typically set to a lower value than ILIM to allow the port to tolerate minor faults without current limiting. Per the IEEE specification, the LTC4266 will automatically set ILIM to 425mA (shown in bold in Table 5) during inrush at port turn-on, and then switch to the programmed ILIM setting once inrush has completed. To maintain IEEE compliance, ILIM should kept at 425mA for all Type 1 PDs, and 850mA if a Type 2 PD is detected. ILIM is automatically reset to 425mA when a port turns off. Table 5. Example Current Limit Settings INTERNAL REGISTER SETTING (hex) RSENSE = 0.5Ω 88 08 89 80 8A 09 8B 00 8E 92 CB 10 D2 40 4A 50 5A 60 52 90 9A PSE CURRENT (A) ILIM Foldback The LTC4266 features a two-stage foldback circuit that reduces the port current if the port voltage falls below the normal operating voltage. This keeps MOSFET power dissipation at safe levels for typical 802.3af MOSFETs, even at extended 802.3at power levels. Current limit and foldback behavior are programmable on a per-port basis. Figure 14 shows MOSFET power dissipation with 802.3af-style foldback compared with a typical MOSFET SOA curve; Figure 15 demonstrates how two-stage foldback keeps the FET within its SOA under the same conditions. Table 5 gives examples of recommended ILIM register settings. 1.0 0.8 PSE CURRENT (A) 0.6 0.5 0.4 0.3 0.2 0.1 0.0 SOA DC AT 90°C 0 10 30 40 50 20 PD VOLTAGE (V) AT VPSE = 58V 60 4266 F14 sA m 75 SO A 2x 80 2.3 af ILIM (mA) 53 106 159 213 266 319 372 425 478 531 584 638 744 850 956 1063 1169 1275 1488 1700 1913 2125 2338 2550 2975 RSENSE = 0.25Ω 88 08 89 80 8A FO 0.7 LD 802.3af FOLDBACK Figure 14. Turn On Currents vs FET Safe Operating Area at 90°C Ambient 1.0 25 C0 CA D0 DA E0 49 40 4A 50 5A 60 52 m 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0 SO A 802.3af FOLDBACK SOA DC AT 90°C 10 30 40 50 20 PD VOLTAGE (V) AT VPSE = 58V 60 4266 F15 Figure 15. LTC4266 Foldback vs FET Safe Operating Area at 90°C Ambient LTC4 75 m 266 F T sA SO 90 A °C OLDB ACK 0.9 75 sA T °C BA CK T 25 0.9 °C 4266fb 20 LTC4266 APPLICATIONS INFORMATION The LTC4266 will support current levels well beyond the maximum values in the 802.3at specification. The shaded areas in Table 5 indicate settings that may require a larger external MOSFET, additional heat sinking, or a reduced tLIM setting. MOSFET Fault Detection LTC4266 PSE ports are designed to tolerate significant levels of abuse, but in extreme cases it is possible for the external MOSFET to be damaged. A failed MOSFET may short source to drain, which will make the port appear to be on when it should be off; this condition may also cause the sense resistor to fuse open, turning off the port but causing the LTC4266 SENSE pin to rise to an abnormally high voltage. A failed MOSFET may also short from gate to drain, causing the LTC4266 GATE pin to rise to an abnormally high voltage. The LTC4266 SENSE and GATE pins are designed to tolerate up to 80V faults without damage. If the LTC4266 sees any of these conditions for more than 180μs, it disables all port functionality, reduces the gate drive pull-down current for the port and reports a FET Bad fault. This is typically a permanent fault, but the host can attempt to recover by resetting the port, or by resetting the entire chip if a port reset fails to clear the fault. If the MOSFET is in fact bad, the fault will quickly return, and the port will disable itself again. The remaining ports of the LTC4266 are unaffected. An open or missing MOSFET will not trigger a FET Bad fault, but will cause a tSTART fault if the LTC4266 attempts to turn on the port. Voltage and Current Readback The LTC4266 measures the output voltage and current at each port with an internal A/D converter. Port data is only valid when the port power is on. The converter has two modes: • Slow mode: 14 samples per second, 14.5 bits resolution • Fast mode: 440 samples per second, 9.5 bits resolution In fast mode, the least significant 5 bits of the lower byte are zeroes so that bit scaling is the same in both modes. Disconnect The LTC4266 monitors the port to make sure that the PD continues to draw the minimum specified current. A disconnect timer counts up whenever port current is below 7.5mA (typ), indicating that the PD has been disconnected. If the tDIS timer expires, the port will be turned off and the disconnect bit in the fault event register will be set. If the current returns before the tDIS timer runs out, the timer resets and will start counting from the beginning if the undercurrent condition returns. As long as the PD exceeds the minimum current level more often than tDIS, it will stay powered. Although not recommended, the DC disconnect feature can be disabled by clearing the corresponding DC Disconnect Enable bits. Note that this defeats the protection mechanisms built into the IEEE spec, since a powered port will stay powered after the PD is removed. If the still-powered port is subsequently connected to a non-PoE data device, the device may be damaged. The LTC4266 does not include AC disconnect circuitry, but includes AC disconnect enable bits to maintain compatibility with the LTC4259A. If the AC Disconnect Enable bits are set, DC disconnect will be used. Shutdown Pins The LTC4266 includes a hardware SHDN pin for each port. When a SHDN pin is pulled to DGND, the corresponding port will be shut off immediately. The port remains shut down until re-enabled via I2C or a device reset in AUTO pin mode. Masked Shutdown The LTC4266 provides a low latency port shedding feature to quickly reduce the system load when required. By allowing a pre-determined set of ports to be turned off, the current on an overloaded main power supply can be reduced rapidly while keeping high priority devices powered. Each port can be configured to high or low priority; all low-priority ports will shut down within 6.5μs after the MSD pin is pulled low. If multiple ports in a LTC4266 device are shut down via MSD, they are staggered by at least 0.55μs to help reduce voltage transients on the main 4266fb 21 LTC4266 APPLICATIONS INFORMATION supply. If a port is turned off via MSD, the corresponding detection and classification enable bits are cleared, so the port will remain off until the host explicitly re-enables detection. SERIAL DIGITAL INTERFACE Overview The LTC4266 communicates with the host using a standard SMBus/I2C 2-wire interface. The LTC4266 is a slave-only device, and communicates with the host master using the standard SMBus protocols. Interrupts are signaled to the host via the INT pin. The timing diagrams (Figures 5 through 9) show typical communication waveforms and their timing relationships. More information about the SMBus data protocols can be found at www.smbus.org. The LTC4266 requires both the VDD and VEE supply rails to be present for the serial interface to function. Bus Addressing The LTC4266’s primary serial bus address is 010xxxxb, with the lower four bits set by the AD3-AD0 pins; this allows up to 16 LTC4266s on a single bus. All LTC4266s also respond to the address 0110000b, allowing the host to write the same command (typically configuration commands) to multiple LTC4266s in a single transaction. If the LTC4266 is asserting the INT pin, it will also respond to the alert response address (0001100b) per the SMBus spec. Interrupts and SMBALERT Most LTC4266 port events can be configured to trigger an interrupt, asserting the INT pin and alerting the host to the event. This removes the need for the host to poll the LTC4266, minimizing serial bus traffic and conserving host CPU cycles. Multiple LTC4266s can share a common INT line, with the host using the SMBALERT protocol (ARA) to determine which LTC4266 caused an interrupt. Register Description For information on serial bus usage and device configuration and status, refer to the LTC4266 Software Programming documentation. EXTERNAL COMPONENT SELECTION Power Supplies and Bypassing The LTC4266 requires two supply voltages to operate. VDD requires 3.3V (nominally) relative to DGND. VEE requires a negative voltage of between –44V and –57V for Type 1 PSEs, or –50V to –57V for Type 2 PSEs, relative to AGND. The relationship between the two grounds is not fixed; AGND can be referenced to any level from VDD to DGND, although it should typically be tied to either VDD or DGND. VDD provides power for most of the internal LTC4266 circuitry, and draws a maximum of 3mA. A ceramic decoupling cap of at least 0.1μF should be placed from VDD to DGND, as close as practical to each LTC4266 chip. Figure 16 shows a three component low dropout regulator for a negative supply to DGND generated from the negative VEE supply. VDD is tied to AGND and DGND is negative referenced to AGND. This regulator drives a single LTC4266 device. In Figure 17, DGND is tied to AGND in this boost converter circuit for a positive VDD supply of 3.3V above AGND. This circuit can drive multiple LTC4266 devices and opto couplers. VEE is the main supply that provides power to the PDs. Because it supplies a relatively large amount of power and is subject to significant current transients, it requires more design care than a simple logic supply. For minimum IR loss and best system efficiency, set VEE near maximum amplitude (57V), leaving enough margin to account for transient over- or undershoot, temperature drift, and the line regulation specs of the particular power supply used. AGND VDD C1 0.1µF Q2 CMPTA92 R5 750k VEE AGND LTC4266 DGND VEE 4266 F16 D1 CMHZ4687-4.3V Figure 16. Negative LDO to DGND 4266fb 22 LTC4266 APPLICATIONS INFORMATION L3 100µH SUMIDA CDRH5D28-101NC R51 4.7k 1% R53 4.7k 1% 5 VCC 1 R58 10 R54 56k C79 2200pF ITH/RUN NGATE 6 Q15 FDC2512 R55 806 1% R56 47.5k 1% C75 10µF 16V D28 B1100 C74 100µF 6.3V L4 10µH SUMIDA CDRH4D28-100NC R52 3.32k 1% C73 10µF 6.3V 3.3V AT 400mA C77 0.22µF 100V C76 10µF 63V + C78 0.22µF 100V Q13 FMMT723 Q14 FMMT723 LTC3803 3 VFB GND 2 SENSE 4 R57 1k R59 0.100 1%, 1W 4266 F17 VEE R60 10 Figure 17. Positive VDD Boost Converter Bypass capacitance between AGND and VEE is very important for reliable operation. If a short circuit occurs at one of the output ports it can take as long as 1μs for the LTC4266 to begin regulating the current. During this time the current is limited only by the small impedances in the circuit and a high current spike typically occurs, causing a voltage transient on the VEE supply and possibly causing the LTC4266 to reset due to a UVLO fault. A 1μF 100V , X7R capacitor placed near the VEE pin is recommended to minimize spurious resets. Isolating the Serial Bus The LTC4266 includes a split SDA pin (SDAIN and SDAOUT) to ease opto-isolation of the bidirectional SDA line. IEEE 802.3 Ethernet specifications require that network segments (including PoE circuitry) be electrically isolated from the chassis ground of each network interface device. However, network segments are not required to be isolated from each other, provided that the segments are connected to devices residing within a single building on a single power distribution system. For simple devices such as small PoE switches, the isolation requirement can be met by using an isolated main power supply for the entire device. This strategy can be used if the device has no electrically conducting ports other than twisted-pair Ethernet. In this case, the SDAIN and SDAOUT pins can be tied together and will act as a standard I2C/SMBus SDA pin. If the device is part of a larger system, contains additional external non-Ethernet ports, or must be referenced to protective ground for some other reason, the Power over Ethernet subsystem (including all LTC4266s) must be electrically isolated from the rest of the system. Figure 18 shows a typical isolated serial interface. The SDAOUT pin of the LTC4266 is designed to drive the inputs of an optocoupler directly. Standard I2C/SMBus devices typically cannot drive opto-couplers, so U1 is used to buffer the signals from the host controller side. External MOSFET Careful selection of the power MOSFET is critical to system reliability. LTC recommends either Fairchild IRFM120A, FDT3612, FDMC3612 or Philips PHT6NQ10T for their proven reliability in Type 1 and Type 2 PSE applications. Non-standard applications that provide more current than the 850mA IEEE maximum may require heat sinking and other MOSFET design considerations. Contact LTC Applications before using a MOSFET other than one of these recommended parts. Sense Resistor The LTC4266 is designed to use either 0.5Ω or 0.25Ω current sense resistors. For new designs 0.25Ω is recommended to reduce power dissipation; the 0.5Ω option is intended for existing systems where the LTC4266 is used as a drop-in replacement for the LTC4258 or LTC4259A. The lower sense resistor values reduce heat dissipation. 4266fb 23 LTC4266 APPLICATIONS INFORMATION 0.1µF VDD LTC4266 INT SCL SDAIN SDAOUT AD0 AD1 AD2 AD3 DGND AGND 0.1µF VDD LTC4266 INT SCL SDAIN SDAOUT AD0 AD1 AD2 AD3 DGND AGND I2C ADDRESS 0100000 0.1µF VDD CPU U1 SCL 200 U2 2k 0100001 200 2k SDA TO CONTROLLER HCPL-063L U3 0.1µF 200 200 SMBALERT 0.1µF GND CPU U1: FAIRCHILD NC7WZ17 U2, U3: AGILENT HCPL-063L HCPL-063L 0.1µF VDD LTC4266 INT SCL SDAIN SDAOUT AD0 AD1 AD2 AD3 DGND AGND • • • LTC4266 0100010 VDD INT SCL SDAIN SDAOUT AD0 AD1 AD2 AD3 DGND AGND 0101110 ISOLATED 3.3V 0.1µF 10µF + ISOLATED GND VDD LTC4266 INT SCL SDAIN SDAOUT AD0 AD1 AD2 AD3 DGND AGND 4266 F18 0101111 Figure 18. Opto-Isolating the I2C Bus 4266fb 24 LTC4266 APPLICATIONS INFORMATION Four commonly available 1Ω resistors (0402 or larger package size) can be used in parallel in place of a single 0.25Ω resistor. In order to meet the ICUT and ILIM accuracy required by the IEEE specification, the sense resistors should have ±1% tolerance or better, and no more than ±200ppm/°C temperature coefficient. Output Cap Each port requires a 0.22μF cap across its outputs to keep the LTC4266 stable while in current limit during startup or overload. Common ceramic capacitors often have significant voltage coefficients; this means the capacitance is reduced as the applied voltage increases. To minimize this problem, X7R ceramic capacitors rated for at least 100V are recommended. ESD/Cable Discharge Protection Ethernet ports can be subject to significant ESD events when long data cables, each potentially charged to thousands of volts, are plugged into the low impedance of the RJ45 jack. To protect against damage, each port requires a pair of clamp diodes; one to AGND and one to VEE (Figure 10). An additional surge suppressor is required for each LTC4266 chip from VEE to AGND. The diodes at the ports steer harmful surges into the supply rails, where they are absorbed by the surge suppressor and the VEE bypass capacitance. The surge suppressor has the additional benefit of protecting the LTC4266 from transients on the VEE supply. S1B diodes work well as port clamp diodes, and an SMAJ58A or equivalent is recommended for the VEE surge suppressor. LAYOUT GUIDELINES Standard power layout guidelines apply to the LTC4266: place the decoupling caps for the VDD and VEE supplies near their respective supply pins, use ground planes, and use wide traces wherever there are significant currents. The main layout challenge involves the arrangement of the current sense resistors, and their connections to the LTC4266. Because the sense resistor values are very low, layout parasitics can cause significant errors. Care is required to achieve specified accuracy, particularly with disconnect currents. Figure 19 illustrates the problem. In the example on the left, two ports have load currents I1 and I2 that return to the VEE power supply through a mutual resistance RM. RM represents the combined resistances of any traces, planes, and vias in the PCB that I1 and I2 share as they return to the VEE supply. The LTC4266 measures the voltage difference between its SENSE and VEE pins to sense the voltage drop across RS1, but as the example shows, RM introduces errors. The example on the right shows how errors can be minimized with a good layout. The circuit is rearranged so that RM no longer affects VS, and the VEE connection to the LTC4266 is used as a Kelvin sense trace. VEE is not I1 I2 LTC4266 GATE SENSE + VS VEE – IEE RK I1 I2 LTC4266 GATE SENSE + VS VEE – IEE RM I1 + I2 + IEE RS1 RS2 RS1 RS2 RM MUTUAL RESISTANCE VS = I1RS1 + I1RM + I2RM KELVIN SENSE LINE I1 + I2 + IEE VS = I1RS1 – IEERK SIGNAL SMALL OFFSET ERROR 4266 F19 SIGNAL SCALE ERROR CROSSTALK ERROR Figure 19. Layout Affects Current Readback Accuracy 4266fb 25 LTC4266 APPLICATIONS INFORMATION a perfect Kelvin connection because all four ports controlled by the LTC4266 share the same sense trace, and because the current through the trace (IEE) is not zero. However, as the equation shows, the remaining error is a small offset term. Figure 20 shows two LTC4266 chips controlling eight ports (A though H). The ports are separated into two groups of four; each has its own trace on the top PCB layer that connects to the VEE plane with a via. Currents from the U1 sub-circuit are effectively isolated from the U2 sub-circuit, reducing the layout problem down to 4-port chunks; this arrangement can be expanded for any number of ports. Figure 21 shows an example of good 4-port layout. Each 0.25Ω sense resistor consists of four 1Ω resistors in PORTS A THROUGH D U1 LTC4266 SENSE1 SENSE2 SENSE3 SENSE4 VEE U2 LTC4266 SENSE1 SENSE2 SENSE3 SENSE4 VEE RSENSE parallel. The four groups of resistors are arranged to minimize the overlap in their current flows, which minimizes mutual resistance. The horizontal slits cut in the copper help to keep the currents separate. Wide copper paths connect each group of resistors to the vias at the center, so the resistance is very low. Proper connection of the sense line is also important. In Figure 21, U1 is not connected directly to the VEE plane but is connected instead to a Kelvin sense trace that leads to the sense resistor array. Similarly, the via at the center of the sense resistor array has a matching hole in the VEE plane. This arrangement prevents the mutual resistance of the four large vias from influencing the current measurements. PORTS E THROUGH H THIS TRACE PROVIDES VEE TO U1 BUT ALSO ACTS AS A KELVIN SENSE LINE FOR PORTS A-D VIA VIA RETURN TO VEE POWER SUPPLY VEE COPPER FILL ON SURFACE LAYER VEE PLANE ON INNER LAYER BY KEEPING THESE COPPER FILLS SEPARATE ON THE SURFACE, MUTUAL RESISTANCE BETWEEN PORTS A-D AND E-H IS ELIMINATED 4266 F20 Figure 20. Layout Strategy to Reduce Mutual Resistance 4266fb 26 LTC4266 APPLICATIONS INFORMATION EDGE OF VEE PLANE (ON SOME INNER LAYER) KELVIN SENSE TRACE CONNECTS U1 TO VEE THROUGH THE VIAS ON THE RIGHT PORT A RSENSE PORT B RSENSE PIN 1 FOUR LARGE VIAS TO VEE PLANE HOLE IN VEE PLANE U1 THE PADDLE IS CONNECTED TO VEE PINS PORT C RSENSE PORT D RSENSE VIAS TO SOURCE PIN OF THE PORT D MOSFET LOCATED ON THE OPPOSITE SIDE OF THE BOARD 4266 F21 Figure 21. Good PCB Layout Example PACKAGE DESCRIPTION GW Package 36-Lead Plastic SSOP (Wide .300 Inch) (Reference LTC DWG # 05-08-1642) 36 19 1.40 ±0.127 15.291 – 15.545* (.602 – .612) 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19 10.804 MIN 7.75 – 8.258 10.11 – 10.55 (.398 – .415) 1 0.520 ±0.0635 18 0.800 BSC RECOMMENDED SOLDER PAD LAYOUT 7.417 – 7.595** (.292 – .299) 0.254 – 0.406 × 45° (.010 – .016) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 2.44 – 2.64 (.096 – .104) 2.286 – 2.388 (.090 – .094) 0.355 REF 0° – 8° TYP 0.231 – 0.3175 (.0091 – .0125) 0.40 – 1.27 (.015 – .050) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2. DIMENSIONS ARE IN (INCHES) 0.800 (.0315) BSC 0.28 – 0.51 (.011 – .02) TYP 0.1 – 0.3 (.004 – .0118) GW36 SSOP 0204 *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.152mm (0.006") PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.254mm (0.010") PER SIDE 4266fb 27 LTC4266 PACKAGE DESCRIPTION (Reference LTC DWG # 05-08-1701 Rev C) UHF Package 38-Lead Plastic QFN (5mm × 7mm) 0.70 ± 0.05 5.50 ± 0.05 4.10 ± 0.05 3.00 REF 5.15 ± 0.05 3.15 ± 0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 5.5 REF 6.10 ± 0.05 7.50 ± 0.05 RECOMMENDED SOLDER PAD LAYOUT APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED PIN 1 NOTCH R = 0.30 TYP OR 0.35 × 45° CHAMFER 37 38 0.40 ±0.10 1 2 5.00 ± 0.10 0.75 ± 0.05 0.00 – 0.05 3.00 REF PIN 1 TOP MARK (SEE NOTE 6) 7.00 ± 0.10 5.50 REF 5.15 ± 0.10 3.15 ± 0.10 (UH) QFN REF C 1107 0.200 REF 0.25 ± 0.05 0.50 BSC R = 0.125 TYP R = 0.10 TYP BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE M0-220 VARIATION WHKD 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 0.20mm 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 4266fb 28 LTC4266 REVISION HISTORY REV B DATE 3/11 DESCRIPTION Revised AGND and DGND pin references throughout data sheet. Revised auto mode to AUTO pin mode throughout data sheet. Added text to Operating Modes and made minor text edits throughout Applications Information section. (Revision history begins at Rev B) PAGE NUMBER 1 to 6, 9, 13 1 to 26 19 to 26 4266fb 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. 29 LTC4266 TYPICAL APPLICATION ISOLATED 3.3V 0.1µF ISOLATED GND DGND AGND 2k VDD CPU U1 SCL 200 2k 200 U2 VDD SCL 1/4 SDAIN LTC4266 SDAOUT INT VEE 1µF 100V X7R HCPL-063L U3 SMAJ58A 200 –48V ISOLATED S1B T1 SENSE GATE OUT 0.22µF 100V X7R FB1 RS 0.25 Q1 S1B FB2 TO CONTROLLER SDA RJ45 CONNECTOR • 200 0.1µF GND CPU HCPL-063L DTSS: DIODES INC SMAJ58A Q1: FAIRCHILD IRFM120A OR PHILIPS PHT6NQ10T U1: FAIRCHILD NC7WZ17 U2, U3: AGILENT HCPL-063L FB1, FB2:TDK MPZ2012S601A T1: PULSE H6096NL OR COILCRAFT ETH1-230LD PHY (NETWORK PHYSICAL LAYER CHIP) • • 0.01µF 200V 75 75 0.01µF 200V INTERRUPT • • 1 2 3 4 5 6 7 8 • • • • 0.01µF 200V 75 75 0.01µF 200V • • 4266 F22 • 1000pF 2000V Figure 22. One Complete Isolated Powered Ethernet Port RELATED PARTS PART NUMBER DESCRIPTION LT3803 LTC4258 LTC4263 LTC4263-1 LTC4265 LTC4267 LTC4268-1 LTC4269-1 LTC4269-2 Constant Frequency Current Mode Flyback DC/DC Controller in ThinSOT™ Quad IEEE 802.3af PoE PSE Controller Single IEEE 802.3af PSE Controller High Power Single PoE PSE Controller IEEE 802.3at PD Interface Controller IEEE 802.3af PD Interface With Integrated Switching Regulator High Power PD With Synchronous Flyback Controller IEEE 802.3at PD Interface Integrated Switching Regulator IEEE 802.3at PD Interface Integrated Switching Regulator COMMENTS 200kHz Operation, Adjustable Slope Compensation DC Disconnect Sensing Only Internal FET Switch With Internal FET Switch 100V, 1A Internal Switch, 2-Event Classification Recognition Internal 100V, 400mA Switch, Dual Inrush Current, Programmable Class No Opto-coupler Required 2-Event Classification, Programmable Classification, Synchronous No-Opto Flyback Controller, 50kHz to 250kHz 2-Event Classification, Programmable Classification, Synchronous Forward Controller, 100kHz to 500kHz 4266fb LT 0311 REV B • PRINTED IN USA 30 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com  LINEAR TECHNOLOGY CORPORATION 2009