Method and Apparatus for a Buck Converter with Pulse Width Modulation and Pulse Frequency Modulation Mode

A buck converter device having a pulse frequency modulation (PFM) where the frequency is fixed, with minimum off-time operation, whose minimum off time is proportional to the 1-D, where D is the duty cycle, the device comprising:

• a comparator providing an output signal of a minimum off time;
• an amplifier;
• and,
• a p-channel MOSFET whose gate is connected to the output of said amplifier providing a signal threshold voltage to a positive terminal of said comparator.

A method of pulse frequency modulation (PFM) with low loads, comprising the following steps:

• providing a buck converter having a PFM mode;
• operating said PFM mode with a fixed frequency, wherein the fixed frequency is set using a minimum off-time;
• and
• setting the minimum off time to be proportional to (1-D), where D is a duty cycle of the buck converter.

A method of pulse frequency modulation (PFM) with low loads comprising of the following steps:

• providing a buck converter comprising of an amplifier, a comparator, a p-channel MOSFET, a first resistor element, a second resistor element, a third resistor element, a capacitor element, a first switch, and a second switch;
• creating a replica of reference voltage Vref proportional to the difference between Vdd and Vref;
• creating a threshold voltage above ground proportional to the difference between Vdd and Vref;
• establishing a voltage on said capacitor whose rate of change is proportional to power supply Vdd;
• establishing a time to charge the capacitor to a threshold voltage proportional to (Vdd-Vref)/Vdd;
• and
• establishing a minimum off time on the output of said comparator.