Detection signature

Hello,

Your circuit is presenting an invalid detection signature, meaning it doesn't look like a 25kOhm resistor with less than 120nF of parallel capacitance. First, the LT4320 is intended for auxiliary input bridges, as shown on page 25 of the LT4295 datasheet. You should use the LT4321 for PoE input bridges as it is designed to not corrupt the detection signature. You can try removing or bypassing the LT4320 as the MOSFETs should act like silicon diodes with it removed to confirm the detection signature becomes valid. Second, C113 should be reduced to 47nF but this likely isn't causing this issue. You also need a bridge on both pairsets which is why the LT4321 controls two full bridges. Right now V3 and V4 is floating.

Best Regards,

Eric

Hello,

Your circuit is presenting an invalid detection signature, meaning it doesn't look like a 25kOhm resistor with less than 120nF of parallel capacitance. First, the LT4320 is intended for auxiliary input bridges, as shown on page 25 of the LT4295 datasheet. You should use the LT4321 for PoE input bridges as it is designed to not corrupt the detection signature. You can try removing or bypassing the LT4320 as the MOSFETs should act like silicon diodes with it removed to confirm the detection signature becomes valid. Second, C113 should be reduced to 47nF but this likely isn't causing this issue. You also need a bridge on both pairsets which is why the LT4321 controls two full bridges. Right now V3 and V4 is floating.

Best Regards,

Eric