AN296 Silicon_Laboratories, AN296 Datasheet - Page 18

• Manufacturer Part Number: AN296
• Description: Using THE Si3400 AND Si3401 POE PD Controllers IN Isolated AND Non-isolated Designs
• Manufacturer: Silicon_Laboratories

AN296
This option may be preferable when a post regulator is required for generation of very low voltages, such as 1.8 V,
or when the post regulator is required for low noise.
With the post regulator option, the larger output voltage will again supply the power. In this case, the Si3400/01 will
attempt to go through the detection and classification cycle, but if the AUX supply is providing the power, the
Si3400/01 will not draw enough dc current, and the PSE may disconnect and cycle continuously. To prevent this, it
is possible to add a 4.7 kΩ, 1 W resistor from VPOSF to VSS of the Si3400/01 to ensure >10 mA power drain from
the PSE. If this resistor is added, the PSE will always have >10 mA power drain and will stay connected even if the
auxiliary power source is providing the load current.
In this option, the PLOSS indicator will not be active when the auxiliary power source is providing the power and
the PSE is not present.
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Rev. 0.8