DC1145B

DC1145B is a demonstration circuit featuring the LTC4267, provides a complete IEEE 802.3af Powered Device (PD) interface and isolated 12V at 0.9A power supply solution for use in Power over Ethernet (PoE) applications. An optional connection is included for a 12V auxiliary supply on the secondary side that disables PoE when present. The LTC4267 integrates the 25k signature resistor, classification current source, thermal overload protection, signature disable and power good signal along with an undervoltage lockout optimized for use with the IEEE required diode bridge. The precision dual level input current limit allows the LTC4267 to charge load capacitors and interface with legacy PoE systems. The LTC4267 combines the above features with a current mode switching controller designed for driving a 6V rated N-channel MOSFET. It features programmable slope compensation, soft-start, and constant frequency operation, minimizing electrical noise even with light loads.

• 39V minimum turn-on voltage at input from PSE, IOUT =100mA
• 33V maximum turn-off voltage at input from PSE
• Operating PoE voltage range from 37V to 57V at input from PSE, IOUT = 0 to max output current
• 350mA maximum input current at input from PSE
• 0.9A maximum output current at input from PSE, VOUT = 12V
• 12V ±2% output voltage at input from PSE, IOUT = 0 to maximum output current
• Class 3, 12.95W PD power class at RCLASS = R7 = 45.3ohm
• Auxiliary input voltage range from 10V to 16V at input from auxiliary supply, dominant over PSE
• 9kohm invalid signature at PD input, auxiliary supply present