PDF LTC4263-1 Data sheet ( Hoja de datos )

Número de pieza	LTC4263-1
Descripción	High Power Single PSE Controller
Fabricantes	Linear Technology
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No Preview Available ! www.DataSheet4U.com LTC4263-1 High Power Single PSE Controller with Internal Switch FEATURES n 30W PSE Output Power n IEEE 802®.3af Compatible n Operation from a Single 56V Supply n Fully Autonomous Operation Without a Microcontroller n Internal MOSFET with Thermal Protection n Precision Inrush Control with Internal Sense Resistor n Forced Current PD Detection for Noise Immunity n AC and DC Disconnect Sensing n Legacy PD Detection n Robust Short-Circuit Protection n Pin-Selectable Detection Backoff for Midspan PSEs n LED Driver Indicates Port On and Blinks Status Codes n Available in a Miniature14-Pin 4mm × 3mm DFN Package APPLICATIONS n High Power Endpoint/Midspan PSEs n Single-Port or Multi-Port Power Injectors n Low Port Count PSEs n Environment B PSEs n Standalone PSEs DESCRIPTION The LTC®4263-1 is a high power, single PSE controller for use in Power over Ethernet systems. The internal current limit and short-circuit protection are designed to provide up to 30W of PSE output power for power hungry PoE applications such as WAPs, security cameras and RFID readers. The LTC4263-1 includes IEEE 802.3af compliant PD detec- tion circuitry along with selectable AC and DC disconnect sensing, allowing seamless operation in conventional IEEE 802.3af systems as well as propriety, high power applications. The LTC4263-1 simpliﬁes PSE implementa- tion, needing only a single supply and a small number of passive support components. Onboard control algorithms provide complete PSE functionality without the need of a microcontroller and built-in foldback and thermal shutdown provide comprehensive fault protection. An LED pin indi- cates the state of the port and detection backoff timing is conﬁgurable for either endpoint or midspan operation. The LTC4263-1 is available in a miniature 14-pin 4mm × 3mm DFN package. L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION Single-Port Fully Autonomous High Power PSE + ISOLATED 56V SUPPLY 0.1μF 100V 0.1μF – LTC4263-1 LED VDD5 LEGACY MIDSPAN VSS SD VSS VDD48 VSS OUT VSS OUT OSC ACOUT 1A SMAJ58A 0.1μF 100V TO PORT MAGNETICS 42631 TA01 42631fa 1 1 page www.DataSheet4U.com TYPICAL PERFORMANCE CHARACTERISTICS LTC4263-1 Powering an IEEE 802.3af PD Powering a Legacy PD with 470μF Bypass Capacitor Overload Restart Delay VDD48 DETECTION DETECTION VOUT PHASE 1 PHASE 2 10V/DIV VSS 100ms/DIV POWER ON VDD48 VOUT 20V/DIV VSS 42631 G01 600mA IOUT 300mA/DIV 0mA 570mA CURRENT LIMIT FOLDBACK 25ms/DIV VDD48 LOAD FULLY CHARGED 42631 G02 VOUT 10V/DIV VSS IPORT 1A/DIV tED 500ms/DIV 42631 G10 Midspan Backoff with Invalid PD Overcurrent Response Time VDD48 VOUT 2V/DIV tDBO RPORT = 15.5k 500ms/DIV VDD48 VOUT 20V/DIV VSS 600mA IOUT 300mA/DIV 0mA 42631 G11 PORT OFF tOVLD LOAD APPLIED 10ms/DIV 42631 G12 Response to PD Removal with AC Disconnect Enabled VDD48 VOUT 10V/DIV VSS PD REMOVAL PORT OFF tMPDO 50ms/DIV 42631 G13 Rapid Response to 1Ω Short VDD48 VOUT 20V/DIV VSS IPORT 20A 20A/DIV 0A 1Ω SHORT APPLIED IPORT = CURRENT IN 1Ω RESISTOR APPLIED TO OUTPUT OF CIRCUIT ON FRONT PAGE 1μs/DIV 42631 G14 Rapid Response to Momentary 33Ω Short VDD48 VOUT 20V/DIV VSS 33Ω SHORT APPLIED SHORT 600mA IPORT CURRENT REMOVED LIMIT ACTIVE 300mA/DIV 0mA FOLDBACK CURRENT LIMIT 100μs/DIV 42631 G15 IPORT = CURRENT IN 33Ω RESISTOR APPLIED TO OUTPUT OF CIRCUIT ON FRONT PAGE 42631fa 5 5 Page www.DataSheet4U.com LTC4263-1 APPLICATIONS INFORMATION accidentally powered. Disconnect with either AC or DC methods using the LTC4263-1 is fully compliant and insures safe power removal after PD disconnect. Com- mand and control for the LTC4263-1 is handled internally without the need of a microcontroller, thereby simplifying system design. LTC4263-1 OPERATION Signature Detection The IEEE 802.3af speciﬁcation deﬁnes a speciﬁc pair-to- pair signature resistance used to identify a device that can accept power via its Ethernet connection. When the port voltage is below 10V, an IEEE 802.3af compliant PD will have an input resistance of approximately 25kΩ. Figure 2 illustrates the relationship between the PD sig- nature resistance and the required resistance ranges the PSE must accept and reject. According to the IEEE 802.3af speciﬁcation, the PSE must accept PDs with signatures between 19kΩ and 26.5kΩ and may or may not accept resistances in the two ranges of 15kΩ to 19kΩ and 26.5kΩ to 33kΩ. The black box in Figure 2 represents the typical 150Ω pair-to-pair termination used in Ethernet devices like a computer’s network interface card (NIC) that cannot accept power. RESISTANCE 0Ω 10k 20k 30k PD 150Ω (NIC) PSE REJECT 23.75k 26.25k ACCEPT 15k 19k 26.5k REJECT 33k 42631 F02 Figure 2. IEEE 802.3af Signature Resistance Ranges The LTC4263-1 checks for the signature resistance by forcing two test currents on the port in sequence and measuring the resulting voltages. It then subtracts the two V-I points to determine the resistive slope while remov- ing voltage offset caused by any series diodes or current offset caused by leakage at the port (see Figure 3). The LTC4263-1 will typically accept any PD resistance between 17kΩ and 29.7kΩ as a valid PD. Values outside this range (excluding open and short-circuits) are reported to the user by a code ﬂashed via the LED pin. 255 FIRST 25k \| SLOPE DETECTION POINT 180 SECOND VALID PD DETECTION POINT 0V-2V OFFSET VOLTAGE 42631 F03 Figure 3. PD 2-Point Detection The LTC4263-1 uses a force-current detection method in order to reduce noise sensitivity and provide a more robust detection algorithm. The ﬁrst test point is taken by forcing a test current into the port, waiting a short time to allow the line to settle and measuring the resulting voltage. This result is stored and the second current is applied to the port, allowed to settle and the voltage measured. The LTC4263-1 will not power the port if the PD has more than 5μF in parallel with its signature resistor unless legacy mode is enabled. The LTC4263-1 autonomously tests for a valid PD con- nected to the port. It repeatedly queries the port every 580ms, or every 3.2s if midspan backoff mode is active (see below). If detection is successful, it then powers up the port. Midspan Backoff IEEE 802.3af requires the midspan PSE to wait two seconds after a failed detection before attempting to detect again unless the port resistance is greater than 500kΩ. This requirement is to prevent the condition of an endpoint PSE and a midspan PSE, connected to the same PD at the same time, from each corrupting the PD signature and prevent- ing power-on. After the ﬁrst corrupted detection cycle, the midspan PSE waits while the endpoint PSE completes detection and turns the port on. If the midspan mode of the LTC4263-1 is enabled by connecting the MIDSPAN pin to VDD5, a 3.2 second delay occurs after every failed detect cycle unless the result is an open circuit. 42631fa 11 11 Page

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