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TPS54260-Q1: Questions about Switching Frequency and Discontinuous Mode/Eco-Mode Boundary

Jim Brinkhurst1
Mastermind 44570 points
Part Number: TPS54260-Q1

Hi Experts

My customer has the following questions about this device:

Section 8.2.2.1 Selecting the Switching Frequency (page 30)

  • “Equation 8 and Equation 9 must be used to find the maximum switching frequency for the regulator, choose the lower value of the two equations. Switching frequencies higher than these values result in pulse skipping or the lack of overcurrent protection during a short circuit.”

Does this mean that setting the shifting frequency to a value above Equation 8 (max skip) forces the regulator into pulse skipping eco-mode (PSM)?

 

Section 8.2.2.11 Discontinuous Mode and Eco-mode Boundary (page 35).

  • Output current of 5mA listed as the boundary between discontinuous conduction mode (DCM) and pulse skipping eco-mode (PSM)
  • Output current of 337mA listed as the boundary between continuous conduction mode (CCM) and discontinuous conduction mode (DCM)

I know these values are specific to the design example. Are there formulas to calculate these boundary values in general?

Thanks for your help.

Best regards,

Jim B

  • 0
    TI__Mastermind 23845 points

    Hi Jim,

    Yes the idea of this is that you still operate at your desired frequency as you increases VIN. Therefore you use the maximum VIN on your design and select a frequency such that you will not skip pulses at higher VIN. 

    Equation 8 will give you a frequency that if that can be controlled with minimum on time. 

    If your chosen frequency is higher than equation 8, then you are correct, the part will start skip pulses at that specific VIN

    As for your second question, yes it is specific for the design example. For PSM and DCM, i don't think there is a formula to calculate that but for DCM to CCM i think you can use the inductor current equation and once your DC load current is equal to half of your peak to peak ripple inductor current then that would be your DCM to CCM boundary current

    Thanks and i hope that helps

    -Arief