2 Floating Ground Hot-Swap Architecture

A high-voltage hot-swap architecture is designed based on the floating ground concept by using the existing low-voltage, low-side, hot-swap controller by TI, the TPS23521 device. The TPS23521 device provides standard hot-swap functions such as hot-plug, inrush current management, undervoltage, overvoltage, overcurrent, and short-circuit protections.

As shown in Figure 2-1, the TPS23521 device uses VEE as a reference and drives the GATE of the hot-swap FET with respect to VEE. Unlike in a standard hot-swap configuration, the controller reference, VEE, is left floating and connected to the load terminal, VOUT, instead of to the system ground, GND. By powering between the VCC and VEE pins through an isolated bias power supply, the system emulates a scalable, floating ground hot-swap architecture making the TPS23521 appropriate for ±400V or 800V rails. The capacitor (CSS), connected between the SS pin and the FET drain through a 1kΩ resistor, determines the slew rate of the GATE voltage during start-up. The CSS is internally connected to the GATE pin, functioning as a gate-to-drain capacitor for Q1. When VCC is applied, the TPS23521 device begins GATE charging and turns on Q1. Once the gate-to-source voltage crosses the VTH, the entire GATE current discharges the CSS capacitor, thereby linearly discharging the drain-to-source (VDS) voltage of Q1. The FET Q1 operates in the Miller plateau region and acts as a source follower, where VOUT follows the GATE with a slew rate determined by the CSS capacitor. When the VDS of Q1 reaches zero, the GATE to VEE voltage increases further to VCC to VEE, enabling Q1 to operate in full conduction mode. The low-side current sensing keeps the overcurrent and short-circuit protections intact during start-up and steady-state conditions.