SNVAA63 March 2023 TPSM365R6
The voltage on the SW pin switches from VIN to –VOUT in an IBB topology instead of from VIN to TPSM365R6 IC GND in a buck application. When the high-side MOSFET turns on, the SW node sees the input voltage. When the low-side MOSFET turns on, the SW node detects the device's SYS_GND, which is tied to the negative output voltage pin, –VOUT. During start-up, VIN rises to achieve the desired input voltage. VOUT starts ramping down after the EN pin voltage exceeds its threshold level and VIN exceeds its UVLO threshold. As -VOUT continues to ramp down, the low level of the SW node follows -VOUT. Figure 2-3 shows the resulting normal, smooth start-up of the output voltage.