The following figure shows the typical setup for a capacitive load application and the internal blocks that function when the device is used. Note that all capacitive loads have an associated "load" in parallel with the capacitor that is described as a resistive load but in reality it can be inductive or resistive.

The first thing to check is that the nominal DC current, I_NOM, is acceptable for the TPS1HC30-Q1 device. This check can easily be done by taking the R_θJA from the Thermal Information section and multiplying the RON of the TPS1HC30-Q1 and the INOM with it, add the ambient temperature and if that value is below the thermal shutdown value the device can operate with that load current. For an example of this calculation see the Applications section.

The second key care about for this application is to make sure that the capacitive load can be charged up completely without the device hitting thermal shutdown. The reason is because if the device hits thermal shutdown during the charging, the resistive nature of the load in parallel with the capacitor starts to discharge the capacitor over the duration the TPS1HC30-Q1 is off. Note that there are some application with high enough load impedance that the TPS1HC30-Q1 hitting thermal shutdown and trying again is acceptable; however, for the majority of applications, the system must be designed so that the TPS1HC30-Q1 does not hit thermal shutdown while charging the capacitor.

With the current clamping feature of the TPS1HC30-Q1, capacitors can be charged up at a lower inrush current than other high current limit switches. This lower inrush current means that the capacitor takes a little longer to charge all the way up. The time that it takes to charge up follows the equation below.

However, because the V_DS for a typical 3.3-A application is much less than the V_BB voltage (V_DS ? 3.3A × 0.03 Ω = 100 mV, V_BB ? 13.5 V), the equation can be rewritten and approximated asThe following figure pictures charge timing.Using this dt calculated based on the current limit, and finding the transient thermal impedance value at half the dt value, the junction temperature rise can be approximated by the Equation 5.

For more information about capacitive charging with high-side switches, see the How to Drive Resistive, Inductive, Capacitive, and Lighting Loads application note. This application note has information about the thermal modeling available along with quick ways to estimate if a high-side switch can charge a capacitor to a given voltage.