SLVSF07 July 2021 TPS7H5001-SP
Once the voltage at CS_ILIM exceeds 1.05 V, the device will execute cycle-by-cycle current limiting. The controller output is turned on at the beginning of each cycle until such point that CS_ILIM voltage reaches the current sense threshold VCS_ILIM, when the output is turned off. At the same time, each time the voltage at CS_ILIM reaches 1.05 V, the capacitor at CHICC is charged via a 80-µA current (hiccup delay current). This hiccup delay current is terminated at the end of the clock cycle. As long as there is still an overcurrent being detected, the cycle-by-cycle limiting will continue until the voltage on CHICC reaches 0.6 V. This cycle-by-cycle limiting period is referred to as the delay mode. As such, the capacitor CHICC can be chosen to dictate the amount of time that the controller will spend in delay mode.
Note that this equation is an approximation since:
After the voltage on HICC pin reaches 0.6 V, the SS pin of the controller is discharged and switching stops. The voltage on HICC is then quickly pulled up to 1 V with the pull-up current limited to approximately 1 mA. Once HICC voltage reaches 1 V, the 1-µA hiccup restart current begins to discharge CHICC. The controller will not switch until HICC voltage falls to 0.3 V. Once the voltage falls to 0.3 V, the controller will initiate its soft-start sequence again. If the overcurrent has disappeared, normal operation will resume. The hiccup time, which is the entire non-switching period, can be calculated using Equation 14.
In summary, the capacitor CHICC on the HICC pin controls the amount of time the controller spends performing cycle-by-cycle limiting before switching stops, and also controls the amount of time switching is disabled before re-start is attempted again. It is recommended to use a minimum of 3.3 nF for CHICC.