LTC4257IS8 Linear Technology, LTC4257IS8 Datasheet
LTC4257IS8
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LTC4257IS8 Summary of contents
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... Power Sourcing Equipment (PSE) applica- tions with quad network power controllers. The LTC4257 is available in the 8-pin SO and low profile (3mm × 3mm) DFN packages. , LTC and LT are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. LTC4257 V ...
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... JA ORDER PART NUMBER LTC4257CS8 LTC4257IS8 Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grades are identified by a label on the shipping container. ...
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ELECTRICAL CHARACTERISTICS temperature range, otherwise specifications are at T SYMBOL PARAMETER R Signature Resistance SIGNATURE V Power Good Output Low Voltage PG_OUT Power Good Trip Point V PG_THRES_FALL V PG_THRES_RISE I Power Good Leakage PG_LEAK R On-Resistance ...
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LTC4257 W U TYPICAL PERFOR A CE CHARACTERISTICS Input Current vs Input Voltage 25k Detection Range 0 25°C A 0.4 0.3 0.2 0 –4 –6 –8 –10 –2 INPUT VOLTAGE (V) 4357 G02 Input Current vs ...
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CTIO S NC (Pin 1): No Connect. R (Pin 2): External Class Select Input. Used to set the CLASS current the LTC4257 maintains during classification. Con- nect a resistor between R and V CLASS NC ...
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LTC4257 U U APPLICATIO S I FOR ATIO The LTC4257 is intended for use as the front end of a Powered Device (PD) designed to IEEE 802.3af draft standard. The LTC4257 includes a trimmed 25k signature resistor, classification current source, ...
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U U APPLICATIO S I FOR ATIO Table 1. LTC4257 Operational Mode as a Function of Input Voltage INPUT VOLTAGE (V with RESPECT to GND) LTC4257 MODE OF OPERATION – 1.4V Inactive – 1.5V to – 10V ...
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LTC4257 U U APPLICATIO S I FOR ATIO Classification Once the PSE has detected a PD, the PSE may optionally classify the PD. Classification provides a method for more efficient allocation of power by allowing the PSE to identify lower-power ...
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U U APPLICATIO S I FOR ATIO probing exceeds 75ms, the LTC4257 may overheat. In this situation, the thermal protection circuit will engage and disable the classification current source in order to protect the part. The LTC4257 stays in classification ...
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LTC4257 U U APPLICATIO S I FOR ATIO is designed to accept this thermal load and is thermally protected to avoid damage to the onboard power MOSFET. Note that the PD designer must ensure that the PD steady- state power ...
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U U APPLICATIO S I FOR ATIO Thermal Protection The LTC4257 includes smart thermal protection in order to provide full device functionality in a miniature package while maintaining safe operating temperatures. Several factors create the possibility for tremendous power dissipation ...
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LTC4257 U U APPLICATIO S I FOR ATIO EXTERNAL INTERFACE AND COMPONENT SELECTION Transformer Nodes on an Ethernet network commonly interface to the outside world via an isolation transformer (Figure 8). For powered devices, the isolation transformer must include a ...
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U U APPLICATIO S I FOR ATIO However, if the standard diode bridge is replaced with a Schottky bridge, the transition points between modes will be affected. The application circuit (Figure 11) shows a technique for using Schottky diodes while ...
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LTC4257 U U APPLICATIO S I FOR ATIO RJ45 + TX 1 – – SPARE – SPARE 8 ISOLATED WALL TRANSFORMER RJ45 + TX 1 – ...
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U U APPLICATIO S I FOR ATIO Classification Resistor Selection (R IEEE 802.3af allows classifying PDs into four distinct classes with class 4 being reserved for future use (Table 2). An external resistor connected from R ure 3) sets the ...
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LTC4257 U U APPLICATIO S I FOR ATIO Load Capacitor IEEE 802.3af requires that the PD maintain a minimum load capacitance of 5µ permissible to have a much larger load capacitor and the LTC4257 can charge very large ...
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U U APPLICATIO S I FOR ATIO Layout The LTC4257 is relativity immune to layout problems. Excessive parasitic capacitance on the R be avoided. If using the DD package, include an electrically isolated heat sink to which the exposed pad ...
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LTC4257 U TYPICAL APPLICATIO 18 4257fb ...
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... RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 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 represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. ...
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... Quad IEEE 802.3af Power over Ethernet Controller LTC4259A-1 Quad IEEE 802.3af Power over Ethernet Controller LTC4267 IEEE 802.3af PD Interface Controller with Integrated Switching Regulator Burst Mode is a registered trademark of Linear Technology Corporation Linear Technology Corporation 20 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 ● ...