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TPSM63606: Maximum voltage out with 12.6V in

WST
Intellectual 945 points
Part Number: TPSM63606

We are using a design like in 9.2.2 of the datasheet, a buck-boost to get Negative output voltage.

According to section 8.3.2 of the datasheet it says that the output can be adjusted from 1V up to a max. of 16V or slightly less than Vin, whichever is lower.
We wanted our output to be about -12.7V with a 12.6V input. 

If I look again at 9.2.2, it shows the input from 9V to 24V and the output at -12V. Since abs[-12V] is > 9V in, does the statement in 8.3.2 of the datasheet apply?
Can I have a slightly higher output voltage (117k / 10k) Rfbt/Rfbb and have it work ok?

I can't find anything else that says the output has to be < then input.

Thanks,
Warren

  • 0
    Intellectual 945 points

    Also, since we are inverting do we need a Cff cap with a -12.7V output? I could lay it out for a part, but I didn't see one in the -12V design mentioned above.

  • +1
    TI__Expert 3766 points

    Hi Warren,

    To answer your inquiry, the equation you are looking for is Vmax >= Vin + |Vout| where Vmax is the maximum voltage the module can handle. The TPSM63606 has a Vmax of 36V, so you can have an output of -12.7V with an input of 12.6V as long as the part doesn't exceed it's Vmax. For more details, also look at this technical article written by my colleague. I would also suggest leaving in a placeholder for the Cff capacitor so the loop stability can be optimized if necessary.

    Regards,

    Henry

  • 0 in reply to Henry Kou
    Intellectual 945 points

    Thanks for the answer. I was thinking of leaving a Cff capacitor location in the design. We are using an EVM board that has the 22pF part on it for analysis. I could take that off to check stability under load changes also.