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TPS62240: 100% Duty Cycle vs Bypass Mode

Bagus Christiandha
Prodigy 10 points
Part Number: TPS62240

Hi I am wondering, what is the difference between TPS62240's 100% Duty Cycle with Bypass mode from other chips (e.g TPS6273)?

In 100% Duty Cycle, will the output voltage follow the input voltage when the input voltage lower than the output voltage?

If yes, how far it will go and what will happen with the output voltage regulation?

Regards,

Bagus

  • 0
    TI__Expert 3611 points

    Hi Bagus,

    There is no difference between them, it is just a different way to describe the same operation. The way this mode operates is described in the datasheet for the TPS62240 on page 9: "The device starts to enter 100% duty cycle mode once the input voltage comes close to the nominal output voltage. To maintain the output voltage, the high-side MOSFET switch is turned on 100% for one or more cycles. With further decreasing VIN the high-side MOSFET switch is turned on completely."

    In 100% mode, VOUT will always be lower than VIN because of the internal resistance of the high-side MOSFET (Rdson) and the DC resistance of the inductor. The voltage drop caused by these two resistances can be calculated as shown in Equation 1 from page 9 in the TPS62240 datasheet: (Rdson+RL)*Iout.

    So VOUT = VIN - (Rdson+RL)*Iout; until VIN decreases below the UVLO (Undervoltage Lockout) threshold, when that happens the output stage of the converter is disabled - VOUT will be 0V.

    Regards,

    Davor