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LMQ61460: Maximum Switching Frequency of Device with High Duty Cycle (Vin:13V, Vout:12V, Iout:1.2A)

Vijay Ravindran
Intellectual 1440 points
Part Number: LMQ61460


Hello team,

The LMQ61460 is being used to buck down a 13V input to a 12V output. The load current necessary is 1.2A. Using Webench, we cannot create a working design using a switching frequency close to the maximum of 2.2MHz. What is the maximum switching frequency supported for this device in this high duty cycle use case? How do we calculate the maximum switching frequency when using a high duty cycle? Is there constraints on Vin when determining maximum switching frequency?

  • 0
    TI__Guru 50120 points

    Edit: meant to calculate the Toff_min to get the minimum input voltage needed. Equations have been changed appropriately.

    Hi Vijay,

    Per datasheet specs the maximum switch duty cycle is roughly 87%. Anything above that may result in the device hitting dropout condition such that output scales to VIN by a diode drop. 

    In order to not be in violation of the minimum typical Ton, the input voltage was calculated to be roughly 14V for a 12V regulation given this switching frequency.

    This was calculated with the following: Fsw = 2.2MHz, Duty cycle = Vout/Vin; Toff_actual = (1 / Fsw) * (1 - D), Toff_actual > Toff_min. 

    Let me know if you have any questions on this. 

    Regards,

    Jimmy