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TPS55340: Boost Topology, but VIN > VOUT?

Brian Angiel
Expert 4070 points
Part Number: TPS55340

Hi team,

I currently use TPS55340 as a Boost in an application where VIN <= 13.3V, VOUT = 13.6V, and IOUT = 800mA. In a new application, VOUT and IOUT remain the same, but VIN may be as high as 13.9V. I'd like to reuse my existing TPS55340 design if possible. What are the drawbacks/consequences of having VIN > VOUT when using TPS55340 in a Boost topology?

I understand the option to pivot to a SEPIC exists, but I would like to understand what to expect with the current design if VIN > VOUT.

Thank you,

Brian Angiel

  • 0
    TI__Guru 65470 points

    Hello Brian,

    In general if VIN is bigger than VOUT, there is a direct path from the input to the output through the inductor and the diode. This means that the device will stop switching and current with flow directly from VIN to VOUT. The device cannot control this, so you do not have any type of current limitation.

    This is the case for all boost converters as this path exists always.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    TI__Expert 4070 points

    Brigitte,

    Thank you. I have a couple clarifying questions:

    1. What if VIN > VOUT but VIN < (Vf + VOUT)? I understand the existence of "direct path" if VIN > (Vf + VOUT), but if VIN is less than the sum of Vf and VOUT, what happens?
    2. Could these scenarios damage TPS55340?

    Brian

  • 0 in reply to Brian Angiel
    TI__Guru 65470 points

    Hello Brian,

    Then the device will not switch until the output is discharged below the set level with the resistor divider and then switch one or some pulses and so on.

    The device will not be damaged by this as long as you stay below the abs max rating (be careful that abs max has to include the switching overshoots).

    Best regards,
    Brigitte