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TPS62088: webench simulation issue input range for 3.3Vout

user4782171
Intellectual 1560 points
Part Number: TPS62088

Hi Team,

   Here have one webench question that need your help for it.

   It's okay to run the simulation for Input 3.5V~5.5V  with 3.3Vout/3A through TPS6208833.  But it can't if use TPS62088 for it. And it will show the issue as following: Calc. duty cycle > duty cycle due to min off time.

   From the datasheet the duty cycle shall can be 100% and the minimum input voltage to maintain output regulation couold be V MIN = VOUT + IOUT,MAX ´(RDS(on) + RL ).

 

Best regards,

Albert Lee.

 

  • 0
    Genius 4910 points

    Hi Albert,

    Thank you for bringing this to our attention.

    Please note that the minimum controllable off time is set to 20ns.  Maximum off time duty cycle is calculated using below formula

    Dmax_toff = 1- IC_toffmin * f sw

    Dmax_toff = 1- 20e-9*3.768e6=0.9246

    The duty cycle is calculated for the device using below formula.

    DutyCycle = (Vout + Iout * (RdsonLS + L.DCR)) / (Vin - Iout * (RdsonHS - RdsonLS))

                       = (3.3 + 3*(0.034454+0.0044))/(3.5-3*(0.0442-0.0344))

                      =0.9844 which is greater than Dmax_toff due to which the design is getting failed.

    We have updated IC_toffmin for TPS6208833 device also now.

    Thanks and Regards,

    Atul

  • 0 in reply to Atul_Kulkarni
    TI__Intellectual 1560 points
    Hi Atul,

    Thanks for it and would you share more information or expalining for following concerns.
    1. Have relate min off time technical documentation of this part?
    2. From your calcuation, the Dmax_toff is 0.9246 but from daatsheet that the part can opertate with 100% duty cycle low dropout operation!?

    Best regards,
    Albert Lee
  • 0 in reply to user4782171
    Genius 4910 points
    Hi Albert,

    We have updated the code and have removed the minimum off time.The designs can be created for lower Vin now,
    The changes will be up on production in our next production release.

    Thanks and Regards,
    Atul
  • 0 in reply to Atul_Kulkarni
    TI__Guru**** 150770 points
    Just to clearly close this thread: there is no minimum off time for the TPS62088x device family. There was simply a misunderstanding in the Webench code which failed designs with lower Vins.