SLVSF02D March 2019 – May 2020 TPS23881
The TPS23881 features two types of foldback mechanisms for complete MOSFET protection.
During inrush, at channel turn on, the foldback is based on the channel voltage as shown in Figure 39. Note that the inrush current profile remains the same, regardless of the state of the 2xFBn bits in register 0x40.
After the channel is powered and the Power Good is valid, a dual-slope operational foldback is used, providing protection against partial and total short-circuit at port output, while still being able to maintain the PD powered during normal transients at the PSE input voltage. Note that setting the 2xFBn bit selects the 2× curve and clearing it selects the 1× curve. See Figure 40.
In addition to the default foldback curves, the TPS23881 has individually enabled alternative foldback curves for both inrush and powered operation. These curves have been designed to accommodate certain loads that do not fully comply with the IEEE standard and requires additional power to be turned on or remain powered. See Figure 39 and Figure 40.
If using the Alternative Foldback curves (ALTIRn or ALTFBn = 1), designers need to account for the additional power dissipation that can occur in the FETs under these conditions.