LTC4274 - Single IEEE 802.3at Power Over Ethernet Controller
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LTC4274 - Single IEEE 802.3at Power Over Ethernet Controller - 1

LTC4274 1 4274fa n PSE Switches/Routers n PSE Midspans APPLICATIONS FEATURES DESCRIPTION Single PoE+ PSE Controller The LTC®4274 is a single power sourcing equipment 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 LTC4274 includes advanced power management features, including current and voltage readback and programmable ICUT and ILIM thresholds. Available C libraries simplify 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 LTC4274 is available in a 5mm × 7mm QFN package that significantly reduces board space compared with competing solutions. n Compliant with IEEE 802.3at Type 1 and 2 n 0.34Ù Total Channel Resistance 130mW/Port at 600mA n Advanced Power Management 8-Bit Programmable Current Limit (ILIM) 7-Bit Programmable Overload Currents (ICUT) Fast Shutdown 14.5-Bit Port Current/Voltage Monitoring 2-Event Classification n Very High Reliability 4-Point PD Detection: 2-Point Forced Voltage 2-Point Forced Current n High Capacitance Legacy Device Detection n LTC4259A-1 and LTC4266 SW Compatible n 1MHz I2C Compatible Serial Control Interface n Midspan Backoff Timer n Supports Proprietary Power Levels Above 25W n Available in 38-Pin 5mm × 7mm QFN Package TYPICAL APPLICATION Complete Ethernet High Power Source 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. 4274 TA01 SCL SDAIN SDAOUT AD0 AD1 AD2 AD3 AGND VEE SENSE –54V 1ìF 100V SMAJ58A GATE OUT PORT 0.22ìF 100V S1B S1B –54V DGND INT SHDN VDD AUTO MSD RESET MID 3.3V 0.1ìF LTC4274

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LTC4274 - Single IEEE 802.3at Power Over Ethernet Controller - 3

LTC4274 3 4274fa ELECTRICAL CHARACTERISTICS SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS –48V Supply Voltage AGND – VEE For IEEE Type 1 Complaint Output For IEEE Type 2 Complaint Output l l 45 51 57 57 VV Undervoltage Lock-out Level l 20 25 30 V VDD VDD Supply Voltage VDD – DGND l 3.0 3.3 4.3 V Undervoltage Lock-out l 2.2 V Allowable Digital Ground Offset DGND – VEE l 25 57 V IEE VEE Supply Current (AGND – VEE) = 55V l –2.4 –5 mA IDD VDD Supply Current (VDD – DGND) = 3.3V l 1.1 3 mA Detection Detection Current – Force Current First Point, AGND – VOUT = 9V Second Point, AGND – VOUT = 3.5V l...

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LTC4274 - Single IEEE 802.3at Power Over Ethernet Controller - 4

LTC4274 4 4274fa SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Current Sense VCUT Overcurrent Sense Voltage VSENSE – VEE, icut1 = hpen = 00h hpen = 01h, cut[5:0] 4 (Note 12) cutrng = 0 cutrng = 1 l l l 180 9 4.5 188 9.38 4.69 196 9.75 4.88 mV mV/LSB mV/LSB Overcurrent Sense in AUTO Pin Mode Class 0, Class 3 Class 1 Class 2 Class 4 l l l l 90 26 49 152 94 28 52 159 98 30 55 166 mV mV mV mV VLIM Active Current Limit in 802.3af Compliant Mode VSENSE – VEE, dblpwr = hpen = 00h VEE = 55V (Note 12) VEE < VOUT < AGND – 29V AGND – VOUT = 0V l l 204 40 212 220 100 mV mV VLIM Active Current Limit in...

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LTC4274 - Single IEEE 802.3at Power Over Ethernet Controller - 5

LTC4274 5 4274fa SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Timing Characteristics tDET Detection Time Beginning to End of Detection (Note 7) l 270 290 310 ms tDETDLY Detection Delay From PD Connected to Port to Detection Complete (Note 7) l 300 470 ms tCLE1 First Class Event Duration (Note 7) l 11 12 13 ms tME1 First Mark Event Duration (Notes 7, 11) l 6.8 8.6 10.3 ms tCLE2 Second Class Event Duration (Note 7) l 11 12 13 ms tME2 Second Mark Event Duration (Note 7) l 19 22 ms tCLE3 Third Class Event Duration CPORT = 0.6ìF (Note 7) l 0.1 ms tPON Power On Delay in AUTO Pin Mode From End of...

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LTC4274 - Single IEEE 802.3at Power Over Ethernet Controller - 6

LTC4274 6 4274fa SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS I2C Timing Clock Frequency (Note 7) l 1 MHz t1 Bus Free Time Figure 5 (Notes 7, 9) l 480 ns t2 Start Hold Time Figure 5 (Notes 7, 9) l 240 ns t3 SCL Low Time Figure 5 (Notes 7, 9) l 480 ns t4 SCL High Time Figure 5 (Notes 7, 9) l 240 ns t5 Data Hold Time Figure 5 (Notes 7, 9) Data into chip Data out of chip l l 60 120 ns ns t6 Data Set-Up Time Figure 5 (Notes 7, 9) l 80 ns t7 Start Set-Up Time Figure 5 (Notes 7, 9) l 240 ns t8 Stop Set-Up Time Figure 5 (Notes 7, 9) l 240 ns tr SCL, SDAIN Rise Time Figure 5 (Notes 7, 9) l 120 ns...

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LTC4274 - Single IEEE 802.3at Power Over Ethernet Controller - 7

LTC4274 7 4274fa TYPICAL PERFORMANCE CHARACTERISTICS Power On Sequence in AUTO Pin Mode Powering Up into a 180ìF Load 802.3af Classification in AUTO Pin Mode 2-Event Classification in AUTO Pin Mode Classification Transient Response to 40mA Load Step Classification Current Compliance VDD Supply Current vs Voltage VEE Supply Current vs Voltage 802.3at ILIM Threshold vs Temperature 100ms/DIV –70 –60 PORT VOLTAGE (V) 10 0 –10 –20 –30 –40 –50 4274 G01 PORT 1 VDD = 3.3V VEE = –54V FORCED CURRENT DETECTION FORCED VOLTAGE DETECTION 802.3af CLASSIFICATION POWER ON GND VEE 5ms/DIV GND 0mA 4274 G02...

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LTC4274 - Single IEEE 802.3at Power Over Ethernet Controller - 9

LTC4274 9 4274fa TYPICAL PERFORMANCE CHARACTERISTICS ADC Noise Histogram Current Readback in Slow Mode ADC Integral Nonlinearity Current Readback in Slow Mode ADC Noise Histogram Port Voltage Readback in Fast Mode ADC Integral Nonlinearity Voltage Readback in Fast Mode ADC Noise Histogram Port Voltage Readback in Slow Mode ADC Integral Nonlinearity Voltage Readback in Slow Mode INT and SDAOUT Pull Down Voltage vs Load Current MOSFET Gate Drive With Fast Pull Down ADC OUTPUT 0 BIN COUNT 300 250 200 150 100 50 6139 6141 4274 G17 6143 6145 6147 VSENSEn – VEE = 110.4mV CURRENT SENSE RESISTOR...

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