[FAQ] Why does my PoE PD EVM continuously power cycle after connecting to an IEEE802.3at compliant PSE?

The MPS (Maintain Power Signature) is an electrical signature presented by the PD to assure the PSE that it is still present after operating voltage is applied. A valid IEEE802.3at MPS consists of a minimum DC current of 10 mA (at a duty cycle of at least 75 ms on every 225 ms). Once started, the PD must present the maintain power signature (MPS) to assure the PSE that it is still present. The PSE monitors its output for a valid MPS, and turns the port off if it loses the MPS.

Here's a previously solved example: https://e2e.ti.com/support/power_management/power_interface/f/204/p/414645/1473028#1473028

 Additional Resources

• Check out TI's PoE landing page: www.TI.com/PoE

• Learn about the IEEE802.3bt standard: Power over Ethernet: Getting Started with the New Standard