Fairchild FPS Series, Руководство по конструкции

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www.fairchildsemi.com/fps
FPS
™
Design Guide
Green FPS™ Feature – Frequency Modulation for EMI
130kHz
131kHz
132kHz
133kHz
134kHz
135kHz
136kHz
137kHz
138kHz
2mS
A
B
C
130kHz 134kHz
138kHz
Sawtooth
Waveform
Ton
Vfb
Vdrain
Idrain
A
B
C
• Fixed frequency oscillators generate Electromagnetic
Interference (EMI) in a narrow band of the frequency spectrum
• Fairchild’s latest FPS devices modulate its frequency over a
±4kHz frequency range
• EMI is thus spread over a wider range of frequencies
• Allows simple EMI filters to be employed for meeting world
wide EMI requirements
• Refer to Application Note AN-4145 Electromagnetic
Compatibility for Power Converters for additional information
Below shows the frequency spectrum waveforms of a fixed frequency device versus a device that employs
frequency modulation.
100kHz Fixed Frequency
FSDH0165
134kHz with Frequency Modulation
FSD210
Peak Level Limit
Peak Level Limit
Peak Waveform
Quasi Peak Waveform