SLVSDW2B December 2018 – November 2020 TPS23755
PRODUCTION DATA
RTN pin provides the negative power return path for the load. It is internally connected to the drain of the PoE hotswap MOSFET, and the DC-DC controller return. RTN must be treated as a local reference plane (ground plane) for the DC-DC controller and converter primary to maintain signal integrity.
Once VVPD exceeds the UVLO threshold, the internal pass MOSFET pulls RTN to VSS. Inrush limiting prevents the RTN current from exceeding a nominal value of about 140 mA until the bulk capacitance (CBULK in Figure 8-1) is fully charged. Inrush ends when the RTN current drops below about 125 mA. The RTN current is subsequently limited to about 0.45 A.
If RTN ever exceeds about 12.3 V for longer than 400 μs, then the PD returns to inrush limiting.