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Original question:

TPS560430: TPS560430X3 feedback

TPS560430: Can't get the 3.3V version of the Simple Switcher to work

Leonard Shustek
Prodigy 30 points
Part Number: TPS560430

Just as in these queries, I can't get TPS560430X3F, the fixed 3.3V version of the Simple Switcher, to work.

https://e2e.ti.com/support/power-management/f/196/t/715590

https://e2e.ti.com/support/power-management/f/196/t/770186?TPS560430-Is-it-O-K-to-leave-FB-pin-open-when-3-3V-fix-output-version-TPS560430X3F-

I have tried all these with the FB pin:

 - leaving it open

- connecting it to SW

- connecting it after the inductor

- connecting it to a resistor divider after the inductor with values chosen from WEBBENCH designer for 3.3V

None of these work, and they all fail in different ways. 

What is the right way to the fixed 3.3V version of the part to work?

  • 0
    TI__Mastermind 34875 points

    Hi Leonard,

    What's top marking of IC package?

    Can you upload the PCB layout for checking?

    B R

    Andy

  • 0 in reply to Andy Chen
    Prodigy 30 points

    Andy,

    Thank you for the response. It looks like I fixed the problem; apparently my experiments with different connections for FB must have damaged the IC. I unsoldered it and put in a new part with FB connected after the inductor (to Vout), and it works.

    I also discovered that adding a 0.1 ufd input capacitor close to the device is important for reliable startup. It's not shown in Figure 18 on page 15 of the spec sheet, although it is shown when you run WEBENCH to create a custom design. 

    Sorry for the false alarm. In addition to adding a note to the spec sheet about what to do with FB for the fixed 3.3V version, you might want to show a 0.1 ufd input capacitor in parallel to the larger one.

    Len