[FAQ] TPS23861: What’s the difference among Auto Mode, Semi-Auto Mode and Manual Mode?

(Refer to TPS23861 datasheet section 7.4)

The main difference among these three operating modes is the flexibility to control the PSE.

In Auto Mode, host control is not needed and TPS23861 can operate by itself (including detection, classification, power on and fault handling). Generally, Auto Mode is widely used in low port count PSE system.

In Semi-Auto Mode, the port automatically performs detection and classification as long as the detection and classification are enabled (0x14). A pushbutton command (0x19h) is required to power on the port. Before the pushbutton command, the port keeps performing detection and classification while a valid PD is connected. If the pushbutton command is issued during one detection or classification cycle, the port will finish the current detection and classification cycle and take the power on action. So when pushbutton is issued doesn’t impact when the port is turned on. ICUT and PoE Plus are not set automatically and they need to be set by the host. This mode is widely used in higher port count systems which need more flexibility to control the PSE (ex. Port power management). For port power management systems consider utilizing TI's TPS23861 PoE MSP430 Reference Code for Multi-Port Power Management Applications

Manual Mode provides the most flexibility to customer. TPS23861 in Manual Mode can force the port to turn on without detection or classification. Another difference from Semi-Auto mode is TPS23861 only does detection and classification once if they are enabled. When the pushbutton command is issued impacts when the port is turned on, so pushbutton command should be set within 22ms after classification is completed if two-event classification is applied in order to meet the IEEE802.3at standard.

 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