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TPS54531: TPS54531

Robert Freehart
Prodigy 80 points
Part Number: TPS54531

I'm using a pair of TPS54531 devices to generate 5V and 3.3V from a 24V source.  I have been going through the datasheet figuring out the components to meet our power requirements.  And then I ran into section 9.2.2.6 Compensation Components.  To calculate the values of these components you need to run a Spice simulation and generate two values to use in Equation 17.  (Actually I'm not sure by description what those values are.)  I don't have access to a spice tool nor do I know how to use one.  I've downloaded and installed TI's Tina tool but I don't know how to use it.  Supposedly Webbench will help but I can't seem to find my way to it.  Is there another way to determine the values of these components?

  • 0
    TI__Genius 10070 points

    Hi,

    Webench is the easiest and most accurate simulation tool, what is the problem when you use it?

    Shawn

  • 0 in reply to Shawn Nie
    Prodigy 80 points

    How do I get to it?

    Okay I got to it, at least the demo it provides.  It won't let me put in our full requirements nor change to the components thus far selected to meet those requirements.

    Naw... If the tool is no better than the demo then this won't do it for us either.  I tried entering more specifications for the design and it just came up with the same BAD answer and won't allow me to put in the correct components to get there.  For example we need the 5V output to be limited to +/-0.1V with 5mV of ripple.  I've already calculated the component values to give us just that but Webench won't allow me to enter those components or just their values.  For example it is definitely STUCK on Rfbt = 10.2k and Rfbb= 1.96k.  But via the equations in the datasheet a better actual 5V can be achieved with Rfbt= 10.5k and Rfbb= 2k. But i can't even make that change.

  • 0 in reply to Robert Freehart
    TI__Guru**** 191445 points

    Robert,

    I'm afraid I am to blame about the datasheet compensation design method.  I've been doing it that way for years.  Unfortunately, TPS54531 does not have an average model, so I generated Figure 11 using an actual measurement.  I was expecting an average model to be subsequently released.  Let me see if we can find a simplified set of equations for compensation.  Also I should note that you may find it difficult to get output ripple below about 7-10 mV without a post filter.  This is not unique to TPS54531.  It applies to most switching supplies above a few hundred mA of load current.