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LM3429: LM3429 Switch Frequency Limitation

Part Number: LM3429

Hi Team,

I saw LM3429 can program switch frequency setting off time via RCT component RT/CT, but has no recommend around minimum - maximum.
Could you help provide switch frequency limitation?

  • Hello Kuo,

    The datasheet specifies "up to 2MHz", but it really depends.

    The minimum Fsw realistically to keep the size and cost down is about 100kHz. Anything lower and things start getting very large and costly.

    The maximum Fsw is really determined by the chosen FET and the application. The FET because you cannot exceed the VCC current limit due to the gate charge (Ivcc = Qg*Fsw). The application because when you start getting to >1MHz frequencies the minimum on time will limit your minimum duty cycle, so you may not be able to operate with VIN close to VOUT.