DC/DC Converter Application Note
PWM Control and VFM Control
Ricoh DC/DC converters are PWM or VFM controlled. PWM is an abbreviation for Pulse Width Modulation and VFM is an abbreviation for Variable Frequency Modulation. (VFM is also called PFM: Pulse Frequency Modulation.)
Each has features as shown in below table.
|Oscillator Frequency||Pulse Width (Duty)||At Low Load||Noise suppression*|
|PWM Control||Constant||Change||Not Good||Low||Easy|
- *) Noise suppression: The VFM control type changes its oscillator frequency depending on the output load. Since the noise varies according to the oscillator frequency, it is possible that noise suppression is difficult. Since the PWM control type has a constant oscillator frequency not varying according to the output load, as a result the noise is also constant and it is easier to take measures to reduce noise.
For optimal use, some products may switch between the two control types. The switching methods include manual switching by means of a MODE pin and automatic switching based on the output load.