QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 804 POWER OVER ETHERNET PD INTERFACE WITH INTEGRATED SWITCHING REGULATOR LTC4267 DESCRIPTION Demonstration circuit 804 is a POWER OVER The LTC4267 combines the above features with a ETHERNET PD INTERFACE WITH current mode switching controller designed for INTEGRATED SWITCHING REGULATOR featur- driving a 6V rated N-channel MOSFET. It features ing the LTC4267. It provides a complete IEEE programmable slope compensation, soft-start, and 802.3af power device (PD) interface and isolated constant frequency operation, minimizing electrical 3.3V power supply solution for use in Power over noise even with light loads. Ethernet (PoE) applications. The DC804 demo board comes in 3 variants, -A, - The LTC4267 integrates the 25k signature resis- B and -C, which output 3, 5 and 8.5 watts, respec- tor, classification current source, thermal overload tively. There is also optional circuitry to provide protection, signature disable and power good sig- alternative secondary side regulation with the nal along with an undervoltage lockout optimized LT4430, a high performance Secondary Side Op- for use with the IEEE required diode bridge. The tocoupler Driver. precision dual level input current limit allows the LTC4267 to charge load capacitors and interface Design files for this circuit board are available. with legacy PoE systems. Call the LTC factory. LTC is a trademark of Linear Technology Corporation Table 1. Performance Summary (T = 25C) A PARAMETER CONDITION VALUE Minimum Turn-on Voltage Input from PSE -39V Maximum Turn-off Voltage Input from PSE -33V Auxiliary input voltage range Input from 24V auxiliary power +38V to +57V Minimum operating voltage I = Maximum rated load -36V out Maximum Input Current Input from PSE 400 mA Version -A, V =3.3V 1.0A out Maximum Output Current Version -B, V =3.3V 1.6A out Version -C, V =3.3V 2.6A out Output Voltage V =48VDC, from PSE, I =max output current 3.3V, typical in out Line (50% to 100% full load) 2%, typical Output Regulation Load (0% to 100% of rated full load) 2%, typical Isolation Voltage Basic Insulation 250VDC 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 804 POWER OVER ETHERNET PD INTERFACE WITH INTEGRATED SWITCHING REGULATOR OPERATING PRINCIPLES Demonstration circuit 804 interfaces with a cus- While every demonstration circuit is equipped with tomers Power-Over-Ethernet test setup per Fig- a jumper and the appropriate resistors to select ure 1. The front end of the demo circuit imple- any of the four classes defined as of this printing, ments the required Ethernet input interface trans- not every demonstration circuit can perform as if former coupling and common-mode termination it were any one of the four classes. That is, through the integrated connector J1. The demon- DC804B-A is designed to produce 3.3V power for stration circuit is setup to allow data to pass in and a class 1 PD, DC804A-B for a class 2 device and back out of the board while the DC804 performs DC804A-C for a class 3. A DC804B-A, for exam- IEEE 802.3af interface functions. The Power ple, cannot deliver sufficient power for a class 3 Sourcing Equipment (PSE) is connected to J1 and device, regardless of the classification jumper po- the PHY is optionally connected to J2. sition. The PD is required to have 0.1uF of capacitance After detection and classification, the PD is po- during detection and this is provided by C2. It is wered up when the input voltage exceeds the also required to have at least 5uF of capacitance LTC4267 turn-on under-voltage lock out (UVLO) after the in-rush circuit, provided by capacitors C1 through a dual-level current-limited power switch. and C9. While the voltage between POUT and VPORTN is above the Power Good trip point, the amperage through the power switch is held below the low- This demo circuit allows detection and power level current limit. When the voltage between classification of the PD per the IEEE 802.3af spe- POUT and VPORTN falls below the Power Good cification. During the detection process of a PD, trip point, the Power Good signal goes active low the LTC4267 displays the proper 25k signature and the amperage through the power switch is resistor. Signature detection may be disabled, if held below the high-level current limit. so desired, by appropriately setting the jumper at JP5. If signature detection is disabled, all inter- face functions of the LTC4267 are also disabled. For the PD to remain powered on, it must present Signature detection, classification, the internal to the PSE both AC and DC components of the power MOSFET switch and POWER GOOD are Maintain Power Signature (MPS). The PD must all disabled. As this demonstration circuit uses the hold the DC MPS by drawing at least 10mA or the POWER GOOD signal, the power regulator is dis- PSE may disconnect power. The DC804 demo abled, as well. circuit can be made to draw the requisite 10mA by enabling the minimum load at JP6. Classification is programmed by the selection of a single external resistor connected to the RCLASS The synchronous flyback converter operates at a pin. The classification can easily be set in this typical switching frequency of 200kHz, controlled demo circuit with the placement of a single jumper by the current mode controller portion of the on JP0, JP1, JP2, JP3, or JP4. LT4267. Galvanic isolation is achieved through transformer T1 and opto-isolator ISO2. 2