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TPS54531: TPS54531

QU YANJIAO
Prodigy 10 points
Part Number: TPS54531


Dear teachers:

About TPS54531, in the SPEC 8.3.3 ，it says that the DCDC can operate at at 100% duty cycle as long as the BOOT-to-PH pin voltage is greater than 2.1 V
Is this to say that if the VIN is 4V at the VOUT I can get a voltage about 4V? That is to say, when the VIN <= VOUT，TPS54531 can run in a through ?

  • 0
    TI__Genius 15135 points

    Hi, Qu 

    When Vin is 4V, the HS switch will keep turn on, the Vout will be Vin-Iout*Rdson(HS)-Iout*DCR(L). Vout will be < Vin. 

    Besides, as BOOT cap is discharging, once trigger BOOTUV, IC will turn on LS switch to charge BOOT cap, it will make Vout < Vin further. 

  • 0 in reply to Zhao Ma
    Prodigy 10 points

    Hi, ZHAO.Thank you a lot. I still have 2 questions:

    1、When TPS54531 works in this situation where the HS switch keeps on , will the feedback function  work ?

    2、When I use TI's tool to simulate (set VIN=4.5V ，VOUT = 4V）,it fails.  The reason is that the tool can only simulate the normal operation of a DCDC, and can not simulate the buck operate at 100% duty cycle. Is my understanding right? 

  • +1 in reply to QU YANJIAO
    TI__Genius 15135 points

    Hi, Yanjiao

    1. Yes, you can think the feedback doesn't work. 

    2. Yes, the Webench doesn't support the simulation for this condition. 

    Besides, based on my experience, doesn't recommend use tps54531 in this condition. 

  • 0 in reply to Zhao Ma
    Prodigy 10 points

    Hi , ZHAO

    Your answers are very important to me. Thank you very much!