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Webench TPS54240 Soft Start Time limit

Walter Brumm
Prodigy 160 points
Other Parts Discussed in Thread: TINA-TI

Hello All,

I am having some issues with power supply sequencing.  I would like a soft start time to 30mS, which corresponds to a SS capacitor of 94nF.  The datasheet specifies a SS capacitor range of .47uF to .47nF, however webench will only allow soft-start times 1ms<Tss<10mS. 

Is there a problem using this value or is this a limitation of the webench simulation?

Thanks,

Walt

  • 0
    TI__Mastermind 41310 points

    Walt,

    The device should work fine with the 94nF capacitor on the SS/TR pin. Simulation for 30ms is a very tall order. The default simulation with the 2nF capacitor is 1.2ms and it takes a few minutes to run. 30ms would exceed the 8 minute limit for simulation in WEBENCH® by a good bit.

    If you really need to run the simulation for 30ms, you could use the TINA-TI reference design or simply export your custom design from WEBENCH® Power designer using the sim export to TINA-TI or Altium. Both would allow you full simulation control over the circuit.

    The TINA-TI simulation will take about 25 minutes to run.

    Britt

  • 0 in reply to Britt Brooks - Online Design Tools
    Prodigy 160 points

    I thought either :
    A) Webench would run the first 8 minutes of simulation, and then stop, or
    b) Webench was trying to imply some instability.

    The time limit makes sense though. Thanks for the help.