Minimum on-time, t_ON-MIN, is the smallest duration of time that the HS switch can be on. t_ON-MIN is typically 65 ns in the LM76005-Q1. Minimum off-time, t_OFF-MIN, is the smallest duration that the HS switch can be off. t_OFF-MIN is typically 95 ns in the LM76005-Q1. In CCM operation, t_ON-MIN and t_OFF-MIN limits the voltage conversion range given a selected switching frequency. The minimum duty cycle allowed is:

And the maximum duty cycle allowed is:

Given fixed t_ON-MIN and t_OFF-MIN, the higher the switching frequency the narrower the range of the allowed duty cycle. In the LM76005-Q1, frequency foldback scheme is employed to extend the maximum duty cycle when t_OFF-MIN is reached. The switching frequency decreases once longer duty cycle is needed under low V_IN conditions. Such a wide range of frequency foldback allows the LM76005-Q1 output voltage to stay in regulation with a much lower supply voltage V_IN. This leads to a lower effective dropout voltage.

Given an output voltage, the choice of the switching frequency affects the allowed input voltage range, solution size, and efficiency. The maximum operational supply voltage can be found by:

At lower supply voltage, the switching frequency decreases once t_OFF-MIN is tripped. The minimum V_IN without frequency foldback can be approximated by:

Considering power losses in the system with heavy load operation, V_IN-MIN is higher than the result calculated in Equation 10. With frequency foldback, V_IN-MIN is lowered by decreased f_SW. When the device is operating in auto mode at voltages near maximum rated input voltage and light load conditions, an increased output voltage ripple during load transient can be observed. For this reason, TI recommends that the device operating point be calculated with sufficient operational margin so that minimum on-time condition is not triggered.