4 Powering Capacitive Loads with Thermal Regulation at Start up

To power large capacitive loads without hiccups, a thermal regulation is required at start-up to prevent the shutdown of the power switch. With thermal regulation at start-up, the power switch regulates the junction temperature less than the thermal shutdown temperature and allows clean start-up with large capacitive loads. The TPS2663 and TPS1663 devices include the thermal regulation at start-up to provide clean start-up with large capacitive loads. Figure 4-1 shows the application circuit with the TPS2663x device.

Figure 4-2 shows the clean start-up with 4.7-mF capacitive load for V_IN of 32 V. The device starts with constant inrush current and then goes into thermal regulation to prevent thermal shutdown and powers up in 65 ms. Without thermal regulation, the start-up time increases even in the order of minutes for charging large capacitive loads. In case of unknown capacitive loads, it becomes difficult to select the appropriate value of inrush current and slew rate for charging output capacitors. With thermal regulation, the designers can achieve fast and reliable startup without selecting the appropriate value of inrush current and output slew rate.
With higher capacitive load, the power switch heats up even faster and thermal regulation is initiated earlier. Figure 4-3 illustrates clean start-up with a capacitive load of 20 mF and V_IN of 32 V.

See TPS2663 Design Calculator to design with the TPS2663 and TPS1663 devices.

Table 4-1 lists the charging time with different capacitive loads and ambient temperatures for the TPS2663 and TPS1663 devices.