One of the parameters that influences the dropout performance of a buck regulator is the minimum off time. As the input voltage is reduced, to near the output voltage, the off time of the high-side switch starts to approach the minimum value (see Electrical Characteristics). Beyond this point the switching may become erratic and/or the output voltage falls out of regulation. To avoid this problem, the LM53625/35-Q1 automatically reduces the switching frequency to increase the effective duty cycle. This results in two specifications regarding dropout voltage, as shown in System Characteristics. One specification indicates when the switching frequency drops to 1.85 MHz; avoiding the A.M. radio band. The other specification indicates when the output voltage has fallen to 3% of nominal. See the Application Curves for typical dropout values. The overall dropout characteristic for the 5-V option can be seen in Figure 19 and Figure 20. The SYNC input is ignored during frequency foldback in dropout. Additional dropout information is discussed in for 5-V output (Application Curves and for 3.3 V output (Application Curves).