QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1049 TRIPLE OUTPUT, HIGH POWER, HIGH EFFICIENCY POE PD LTC4264CDE, LTC3825EFE DESCRIPTION Demonstration circuit 1049 is a high-power triple out- cation that requires no opto-isolator allowing for low- put supply featuring the LTC4264 with the LTC3825. parts count. The DC1049 output supplies are 5V This board acts as a pre-standard high power Power- 2A, 11.8V 0.27A, and 3.3V 2.5A. over-Ethernet (PoE) Powered Device (PD) and con- DC1049 also demonstrates the use of an auxiliary nects at the RJ45 to a compatible high power Power 24V wall adapter. When present, the auxiliary supply Sourcing Equipment (PSE) device. The LTC4264 pro- becomes the dominant supply over PoE to provide vides IEEE802.3af standard PoE PD interfacing. power to the LT3825. When the PD is fully powered, the LTC4264 switches Design files for this circuit board are available. Call power over to the LTC3825 through an on-board high the LTC factory. power MOSFET. LTC is a trademark of Linear Technology Corporation The highly-integrated LTC3825, small supply utilizes an isolated flyback topology with synchronous rectifi- Table 1. Typical Performance Summary (T = 25C) A PARAMETER CONDITION VALUE PoE Input Voltage In from PSE 37V to 57V I Enabled, Nominal Current 750mA LIM EN PoE Input High Current Limit I Disabled, Nominal Current 1.45A LIM EN SHDN Enabled 23.25k to 26.00k PoE Signature Resistance SHDN Disabled, Maximum Value 11.8k 24V Auxiliary Input Voltage In from Auxiliary Supply 22.8V to 57V 5V 2.5% 2A V from PoE 11.8V 2% 0.27A IN Output Voltage V 3.3V 3% 2.5A OUT 5V 2.5% 2A (NOTE) V from 24V 5% Auxiliary Supply 11.8V 2% 0.27A IN 3.3V 3% 2.5A 5V: < 20mVpp 2A Typical Output Ripple V V = 48V 11.8V: < 100mVpp 0.27A OUT IN 3.3V: < 20mVpp 2.5A Nominal Switching Frequency 250kHz Isolation Voltage 1500VDC NOTE: Output power is rated to not exceed PoE maximum input power with I Enabled. LIM EN 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1049 TRIPLE OUTPUT, HIGH POWER, HIGH EFFICIENCY POE PD QUICK START PROCEDURE DC1049 is easy to set up to evaluate the performance tion applied across V+ and POE- if PSE is not of the LTC4264 with the LTC3825 in a high power PD available (diode bridge is bypassed). application. Refer to Figure 1 and Figure 2 for proper b) Auxiliary: Connect a 24V Auxiliary Supply at J3 measurement equipment setup and follow the proce- or 22.8V to 57V option applied across AUX+ dure below: and AUX- if wall adapter is not available. 1. Place test equipment (voltmeters, ammeters, and 3. Check for the proper output voltages 5V, 11.8V, loads) across outputs 5V, 11.8V, and 3.3V. and 3.3V. 2. Input Supply Options: 4. Once the proper output voltages are established, a) PoE: Connect a high power PSE with a CAT5 adjust the loads within the operating range and ob- cable to RJ45 connector J1 or 37V to 57V op- serve the output voltage regulation, ripple voltage, efficiency and other parameters. OPERATING PRINCIPLES A compatible high power PSE is connected to the Once power is switched over to the LTC3825, the de- DC1049 at the RJ45 connector J1. A diode bridge is vice regulates the output voltages by sensing the av- required by IEEE802.3af across the data pairs and erage of all the output voltages via a transformer spare pairs. Schottky diodes are used at the input to winding during the flyback time. This allows for tight improve efficiency over standard diode bridges. A output regulation without the use of an opto-isolator, high power specific Ethernet transformer is used on providing improved dynamic response and reliability. the data pairs. The LTC4264 provides IEEE802.3af Synchronous rectification increases the conversion standard PoE 25k signature resistance and has the efficiency and cross-regulation effectiveness above a option of displaying a power class through jumper conventional flyback topology. No external driver ICs JP3. When the PD is fully powered, the LTC4264 lim- or delay circuits are needed to achieve synchronous its the inrush current. When voltage is above the turn rectification a single resistor is all that is needed to on UVLO, the LTC4264 signals a power good to the program the synchronous rectifiers timing. LTC3825 to begin operation and switches power The DC1049 also demonstrates accepting input through its onboard power MOSFET. The LTC4264 power from a 24V auxiliary supply (wall wart) con- implements a high current limit of 750mA. Higher nected at J3. When present, the LTC4264 is disabled currents are allowed by disabling the current limit through Q5 to give the auxiliary supply priority over through JP2 on the DC1049. The LTC4264 can also supplying power to the output and not require power be shutdown through JP1 to disable the functions from a PSE. In a high power PD application that does including turning off the internal MOSFET and pre- not use the auxiliary supply, D15 can be shorted for senting an invalid signature resistance to a PSE. higher efficiency in the PD. 2