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TPS54260: power management forum

BADAL KUMAR6
Prodigy 130 points
Part Number: TPS54260

Hi team,

i want to know how it  is possible 100% duty cycle for the DC-DC buck converter like tps54260?. if d=1 then mosfet will remains on and there will drop in Rds(on) and energy stored in inductor is not free wheel anywhere which will leads in the unstable operation. so, could you please explain me the reason?.

regards and thanks,

badal kumar

  • 0
    TI__Mastermind 23845 points

    Hi,

    Yes you are correct. What it assumes is in ideal condition where Rdson is 0 and no DCR in the inductor and the BOOT - SW voltage is maintained at 2.1V typical. 

    Therefore the high side FET can turn on most of the time and VIN = VOUT just as if you have short between VIN and VOUT. Since VIN = VOUT then the voltage across the inductor will be 0.

    If you assume the non-ideal condition then yes the duty cycle will be less than 100%

    Thanks

    -Arief

  • 0 in reply to Arief Hernadi
    TI__Prodigy 130 points

    yes you are correct only in non-ideal condition duty cycle can be 100%. but if d=1 then inductor will get less time to discharge which may lead the device to unstable operation. so, my question is about inductor ?

    thanks and regards,

    badal kumar

  • 0 in reply to BADAL KUMAR6
    TI__Mastermind 23845 points

    Hi,

    Yes but at the same time the VIN is close to VOUT, therefore VIN-VOUT/L = delta IL/ delta T. 

    Therefore at duty cycle close to 1 the peak to peak current ripple is small because the voltage across the inductor is close to 0. 

    The operation should be stable since even though the on time is large but the rise of inductor current is small and during off time the inductor current goes back to the initial current position to maintain volt second balance

    Thanks

    -Arief