ADP2300 PFM/PWM mode

Hi,

I have a queston about ADP2300.
The Datasheet says this device has the automatic transition between PFM and PWM.
But I want to konw how much output curennt trigers PFM mode in general.
Because this device is usd for the analog circuit directly in my system.

I know the transition current depends on Vin, Vout and inductor.
But it would be great if there is a way to predict it.

Best regards,
Tarzan

  • 0
    •  Analog Employees 
    on Mar 21, 2014 8:22 PM

    Hi Tarzan,

    If you are worried about PFM, then you might consider switching to an ADP2370.  This part has a mode pin that allow it operate in force PWM mode so there is no transition to worry about.  This part will also probably give you better efficiency since it is synchronous and will be a smaller solution. 

    In terms of when the ADP2300 will go into PFM.  If you use the ADISimpower tool and look at the efficiency curve for your design, you will often see an abrupt change in slope.  This is when the part goes from CCM to DCM.  PFM will only occur once the pulse width goes below the minimum ontime

    If you use the equations below you can calculate t1 (on time).  If you set t1 = minimum on time from the datasheet you can solve for the approximate Iout where PFM will occur.

        V1 = Vin - Vout - Iout * (FET1_RDSon + dcr)

        V2 = -Vout - Vf - Iout * dcr

          t1 = Sqr(2 * Iout * L * Ts / (V1 - V1 ^ 2 / V2))

          t2 = (-V1 / V2) * t1

          t3 = Ts - t1 - t2

    V1= ontime voltage across inductor

    V2 = off time voltage across inductor

    Iout = output current

    Vf = forward voltage of diode

    t1 = ontime on switch

    t2 = on time of diode

    t3 = dead time

    SQR = square root function

    Ts = period of clock (1/Fsw)

    Fsw = switching frequency

    DCR = DCR of inductor

    FET1_RDSon = rdson on the high side FET

    L = inductance

    Regards,

    Kevin

  • Hi kevin,

    Thank you for the detailed explanation.

    I see your points, so I will check how it actuallly works on the eval-board.

    Best regards,

    Tarzan

  • 0
    •  Analog Employees 
    on Aug 2, 2018 2:36 PM
    This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

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    EZ Admin