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TPS54302: Part behavior if requested output voltage is reduced

Rob Gaddi
Prodigy 130 points

Part Number: TPS54302

I have an application coming up that I'd like to use the TPS54302 for with a dynamically switched output between 24 and 12V (analog switch in the feedback path).

Load current could vary substantially in this application, anywhere from 1mA to 1A; components will have to be sized to handle the 1A case, so I'll have a fair amount of output capacitance.  So if I'm outputting 24V at a light load, then switch my ask to 12V, how should I expect the TPS54302 to behave?  Will it simply pulse skip until the load slowly draws the output down to 12V, at which point it starts introducing contribution from the VIN again?  Or is something silly going to happen?

  • 0
    TI__Genius 14190 points

    Hi,

    How much is the light load when output changed 24V to 12V ? and How long it will take for this output voltage to change ?

    BRs,

    Young

  • 0 in reply to Young Zhao
    Prodigy 130 points

    I haven't done all the numbers yet, but let's say ballpark I've got 10uF and the load is only 1mA.  So when I switch the feedback network, the feedback voltage will be too high for 0.12 seconds while the light load slowly drags the charge back out of those output caps.

  • +1 in reply to Rob Gaddi
    TI__Genius 14190 points

    Hi Rob,

    Here is my thinking about this kind use. Let's take 2 kinds example to discuss.

    1.Vout change : 12V-->24V . For tps54302, it will sense the output (FB voltage) is less than expected and will increase the duty to support 24V.

    2.Vout change :24V -->12V, For tps54302, it will sense the output (FB voltage) is larger than expected and will decrease the duty to support 12V. if the change happened quickly enough , the transient would be smooth . If the change is slow , it may trigger OVP protection . When the FB pin voltage goes above 108% × Vref, the high-side MOSFET is forced off. When the FB pin voltage falls below 104% × Vref, the high-side MOSFET is enabled again. So this transient is also related with the loading condition , as the larger loading will make the output drop quick. So if the loading is too light , say no loading at worst , the output voltage may takes longer enough time to drop lower than 104% x Vref.

    BRs,

    Young

  • 0 in reply to Young Zhao
    Prodigy 130 points

    That's good news; that's fine for my application.  This is all about power saving, so I don't need the output voltage to drop to 12V quickly -- I just don't want to keep investing power to keep it at 24.

  • 0 in reply to Rob Gaddi
    TI__Genius 14190 points

    Hi Rob,

    got you . I will close this case first and pls feel free to re-open it if you have any other question .

    Young