SLVSF02D March 2019 – May 2020 TPS23881
The TPS23881 supports 1- and 3-bit shutdown priority, which are selected with the MbitPrty bit of General Mask register (0x17).
The 1-bit shutdown priority works with the Port Power Priority (0x15) register. An OSSn bit with a value of 1 indicates that the corresponding port is treated as low priority, while a value of 0 corresponds to a high priority. As soon as the OSS input goes high, the low-priority ports are turned off.
The 3-bit shutdown priority works with the Multi Bit Power Priority (0x27/28) register, which holds the priority settings. A port with “000” code in this register has highest priority. Port priority reduces as the 3-bit value increases, with up to 8 priority levels. See Figure 38.
The multi bit port priority implementation is defined as the following:
Prior to setting the MbitPrty bit from 0 to 1, make sure the OSS input is in the idle (low) state for a minimum of 200 µs, to avoid any port misbehavior related to loss of synchronization with the OSS bit stream.
The OSS input has an internal 1-µs to 5-µs deglitch filter. From the idle state, a pulse with a longer duration is interpreted as a valid start bit. Ensure that the OSS signal is noise free.
To ensure both channels of a 4-pair port are disabled during and OSS event, make sure both channel have the same configurations in the 0x15 or 0x27/28 registers.