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TPS6594-Q1: How to prevent to enter into Discontinuous Conduction Mode(DCM)?

TAEHYUN KIM
Prodigy 210 points
Part Number: TPS6594-Q1
Other Parts Discussed in Thread: TDA4VM,

Hello.

I use TPS65941212 and TPS65941111 for powering TDA4VM.

But there are situations entering into DCM at buck converter SW node.

How to prevent to enter into Discontinuous Conduction Mode(DCM)?

the buck converter settings are ( buck1/2/3 Multi Phase , Multi phase adding/shedding , PWM to PFM auto , Spread Spectrum , Switching freq = 2.2MHz , Vin = 3.3V , Vout = 0.85V , 470nH , 47uFx2 on per phase , 47uF on the Load (VDD_CPU1~8 of TDA4VM) )

simply I think it needs to change the inductance for preventing to enter into DCM.

so Could you please recommend the value of inductance?

best regards.

  • 0
    TI__Mastermind 49301 points

    Hi Mr. Kim,

      The "DCM" mode is not caused by inductance; it's caused by transient load. Whenever the load lower than certain level (the level depends on VIN, VOUT and phase configuration), the device enters into PFM mode that you named it "DCM" mode.  

      To prevent the device entering into PFM mode, you can change the BUCKn_FPWM bit from 0 to 1 to force the BUCKn working in PWM mode if you don't care the efficiency when load is low. Copied below from datasheet is for your reference about the mode change: 

    10.3.2.1.3 Transition Between PWM and PFM Modes
    Force PWM mode operation with phase-adding or shedding optimizes efficiency at mid-to-full load. The
    TPS6594-Q1 converter operates in PWM mode at load current of about 600 mA or higher. The device
    automatically switches into PFM mode for reduced current consumption when forced-PWM mode is disabled
    (BUCKn_FPWM = 0) at lighter load-current levels. A high efficiency is achieved over a wide output-load-current
    range by combining the PFM and the PWM modes.

       

    Thanks!

    Phil