• State TI Thinks Resolved
  • Locked Locked
  • Replies 12 replies
  • Answers 5 answers
  • Subscribers 63 subscribers
  • Views 382 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS54425: Conditions under which webench does not work

Shuji Ishiwata
Genius 5905 points
Part Number: TPS54425
Other Parts Discussed in Thread: TPS565208, TPS565201, TPS566231, TPS566238

Hi All,

I have a question about TPS54425.

I tried the simulation with webench under the following conditions, but it didn't work.

Does the following condition not work?
   VIN      =  5V (± 5%)
   VOUT  =  3.3V
   IOUT   =  4A


If it doesn't work, please tell me the reason.

Best Regards,
Ishiwata

  • 0
    TI__Expert 4750 points

    Hi Ishiwata,

    We are able to replicate the issue. Currently analyzing to verify if its a valid fail.
    Shall keep you updated on the fix.

    Thanks and Regards,
    Umayal

  • 0 in reply to Umayal Ramanathan
    Genius 5905 points

    Hi　Umayal


    Thank you for your reply.

    Please analyze it.

    Is it possible to operate under the following conditions as product specifications?

      VIN      = 5V (± 5%)
      VOUT  = 3.3V
      IOUT    = 4A


    Best Regards,
    Ishiwata

  • 0 in reply to Shuji Ishiwata
    TI__Expert 4750 points

    Hi Ishiwata-San,

    We had a discuss with our product expert and found that device TPS54425 will not regulate vout well for above mentioned input condition.

    Alternatively we recommend devices TPS565201,TPS565208 and TPS56623x(TPS566231,TPS566238) for above mentioned input condition. 

    Kindly revert back to us on any further queries.

    Thanks and Regards,

    Umayal

  • 0 in reply to Umayal Ramanathan
    Genius 5905 points

    Hi　Umayal-san,

    Thank you for your reply.

    I want to know TPS54425 will not regulate vout well for above mentioned input condition.

    Please tell me the reason.

    I need to explain for customers who try to use  these conditions.


    Best Regards,
    Ishiwata

  • 0 in reply to Shuji Ishiwata
    TI__Expert 4750 points

    Hi Ishiwata-San,

    Moving this post to product expert group to address the query. 

    Thanks and Regards,

    Umayal

  • 0 in reply to Shuji Ishiwata
    TI__Mastermind 21795 points

    Ishiwata-san,

    For the input conditions, the design will likely run into minimum off-time issues. With increasing currents, the output voltage can start drooping and regulation will suffer. Also, during transient events, due to this limitation, there could be significant undershoot on this device. Suggest looking into TPS566231/8 which has much smaller min off-time and is designed to work well with larger duty cycles.

    Thanks,

    Amod

  • 0 in reply to Amod Vaze
    Genius 5905 points

    Hi Amod-san,

    Sorry for the late reply.　Thank you for your reply.
    The customer is mass-producing under the following conditions, and it is working properly and there is no issue.

        VIN      =  5V (± 5%)
        VOUT  =  3.3V
        IOUT   =  4A

    If there is issue, is there a way to improve it by changing the peripherals without changing the device?

    Best Regards,
    Ishiwata

  • 0 in reply to Shuji Ishiwata
    TI__Mastermind 21795 points

    Hi Ishiwata-san,

    Yes the device is possibly at the edge of minimum off-time so it might work specifically for your conditions. It may enter that at higher temperatures or under transient conditions might cause larger undershoots. If it enters minimum off-time situation, there is no good way to counter the effects as this is inherent behavior of the device.

    Thanks,

    Amod

  • 0 in reply to Amod Vaze
    Genius 5905 points

    Hi Amod-san,


    Thank you for your answer.

    Is it effective to make the inductor smaller and the capacitor larger to improve the transient conditions?


    Best Regards,
    Ishiwata

  • 0 in reply to Shuji Ishiwata
    TI__Mastermind 21795 points

    Hi Ishiwata-san,

    Smaller inductor will speed up the transient response from overshoot perspective but if the device enters minimum off-time zone then the undershoot will still be large. Also, since the TPS54425 is internally compensated, it is recommended to stick with the datasheet L-C combinations.

    Thanks,

    Amod

  • 0 in reply to Amod Vaze
    Genius 5905 points

    Hi Amod-san,

    Thank you for your reply. understood.

    I have additional questions.
    I saw the past E2E.
    e2e.ti.com/.../1583669

    　" I usually recommend max duty cycle of 65% for best possible performance. "
    There is a description.

    Is there a 65% reason? Please tell me the rationale for 65%.

    　For example, as below
    　　　When the slew rate is XX[A/usec], the voltage fluctuation is set to 65% so that it becomes XX[mV] or less.


    Best Regards,
    Ishiwata

  • 0 in reply to Shuji Ishiwata
    TI__Mastermind 21795 points

    Hi Ishiwata-san,

    Yes John Tucker is referring to the same phenomenon we have been talking about and that the max duty cycle is actually limited by the minimum off-time and the switching frequency. 65% duty cycle is possibly just a conservative limit to ensure you are safely out of the min off-time region where regulation will suffer. But in reality, the max duty cycle number will change depending on the combination of min off-time (typ to max varies) and frequency (function of input, output voltage and load)

    Hope this helps.

    Thanks,

    Amod