SLVSF02D March 2019 – May 2020 TPS23881
Disconnect is the automated process of turning off power to the port. When the port is unloaded or at least falls below minimum load, it is required to turn off power to the port and restart detection. In DC disconnect, the voltage across the sense resistors is measured. When enabled, the DC disconnect function monitors the sense resistor voltage of a powered port to verify the port is drawing at least the minimum current to remain active. The TDIS timer counts up whenever the port current is below the disconnect threshold (6.5 mA or 4.5 mA depending on the port configuration). If a timeout occurs, the port is shut down and the corresponding disconnect bit in the Fault Event Register is set. In the case of a PD implementing MPS (maintain Power Signature) current pulsing, the TDIS counter is reset each time the current goes continuously higher than the disconnect threshold for at least 3 ms.
The TDIS duration is set by the TMPDO Bits of the Timing Configuration register (0x16).
If a Class 4 or lower 4-Pair Single Signature PD is connected, the TPS23881 will immediately power down one channel immediately after (no TMPDO timeout) the current falls below the disconnect threshold while leaving the second channel powered. This channel will be re-powered if the current on the remaining channel exceed 75mA. Alterntively if the current on the remaining channel falls below the disconnect threshold for longer than the TMPDO timeout, the port will be shut down and the corresponding disconnect bits in the Fault Event Register are set.
If both channels of a 4-Pair Dual Signature PD are powered, the DCDTx bit in register 0x2D is automatically set after turn on to ensure the IEEE compliant 4.5mA threshold is used.
If a 4-Pair Single Signature Class 5-8 PD is powered, the DCDTx bit in register 0x2D is automatically set after turn on to ensure the IEEE compliant 4.5mA threshold is used.