7.3.14 Voltage Dropout

Voltage dropout is the minimum difference between the input voltage and output voltage that is required to maintain output voltage regulation while providing the rated output current.

To ensure the LMZM33604 maintains output voltage regulation at the recommended switching frequency, over the operating temperature range, the following requirements apply:

For output voltages ≤ 5 V, the minimum V_IN is 3.5 V or (V_OUT + 1 V), whichever is greater.

For output voltages > 5 V, the minimum V_IN is (1.1 × V_OUT).

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However, if fixed switching frequency operation is not required, the LMZM33604 operates in a frequency foldback mode when the dropout voltage is less than the recommendations above. Frequency foldback reduces the switching frequency to allow the output voltage to maintain regulation as input voltage decreases. Figure 41 through Figure 44 show typical dropout voltage and frequency foldback curves for 5 V and 12 V outputs at T_A = 25°C. (As ambient temperature increases, dropout voltage and frequency foldback occur at higher input voltages.)