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TPS61240: I cannot exactly understand the concept of pulse frequency mode(PFM) and Discontinuous mode(DCM)

Yunsik Chung
Intellectual 1150 points
Part Number: TPS61240

Hi,

I was studying about boost converter and i was confused about term 'PFM' and 'DCM'.

If I understood these correctly, PFM is pulse frequency modulation which modulate output voltage by changing the frequency of switch when load out current is low.

DCM is discontinuous current mode which occurs when load out current gets low so inductor current goes to zero.

do they have any relationship?

and also i heard in particular application, people use PFM, DCM in purpose.

What is the advantage of using these modes?

thanks,

Yunsik

  • 0
    TI__Mastermind 34201 points

    Hi Yunsik,

    In power save mode the converter only operates when the output voltage trips below a set threshold voltage. It ramps up the output voltage with several pulses and goes into power save mode once the output voltage exceeds the set threshold voltage. In PWM, the device never skips pulses. The advantage is high efficiency at low load current.

    DCM means discontinuous current mode. The inductor current never goes below zero. CCM means continuous current mode and inductor current can be below zero. 

    DCM and PFM are two thing so they don't have forced relationship.

  • 0 in reply to Zack Liu
    TI__Intellectual 1150 points

    Thank you so much!

    I really appreciate it.

    regards,

    Yunsik