• State TI Thinks Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 3 answers
  • Subscribers 61 subscribers
  • Views 107 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.

LP8758-B0: Load transient and phase adding

user4811888
Intellectual 530 points
Part Number: LP8758-B0

Hi expert,

I see from the datasheet that there's auto phase adding/shedding functions to improve light-load efficiency. As I understand it is only designed for steady-state operation, and Fig40/41 shows phase transition period when load changes, as you know it's impossible for instant output current feedback sensing, phase adding/shedding must have de-glitch time to execute. 

My question is, when dynamic load happens, e.g. 1A to 15A, it's impossible for only original one phase to handle such high current load-step up, is there any non-linear feature inside to quickly add all 4 phases at the same time? And how is the behavior, I mean turn on 4 phases totally overlap(miss interleaving) or still interleaving? It is better to explain if you have waveforms tested for it.  

Thanks for your help.

  • 0
    TI__Genius 11020 points

    Hello,

    To allow fast adding of phases, if the output voltage drops >10mV below the target phases are added immediately. Phases will be still interleaved. 

    In steady state condition buck controls the slave phases depending on load current. Slaves are added/shed depending on load measurement and active phases to optimize efficiency. 

    Thanks.

    Regards,

    Tomi Koskela

  • 0 in reply to Tomi Koskela
    Intellectual 530 points

    Hello, 

    thanks for your answer.

    I've got it however could you please help show me a figure about how adding 4 phases SW waveforms be like?

  • 0 in reply to user4811888
    TI__Genius 11020 points

    Hello,

    I have assigned this thread to product expert. Note there can be delays due to US public holiday. 

    Could you let us know what concern you have about the operation and why do you need this information? If it is just trying to find out how we have designed the device, please understand we cannot disclose all the details. 

    Thanks.

    Regards,

    Tomi Koskela

  • 0 in reply to Tomi Koskela
    Intellectual 530 points

    Hi Tomi,

    Understand that design details should be kept confidential, and please be noted I'm not interested in, or intended for design parameters and details.

    Just from my application and study perspective,  it looks fixed-frequency peak current mode with master-slave control is used for multi-phase control and current sharing. It is important to know if any non-linear SW(PWM) behaviors of sudden all phases adding operation, in order to evaluate the max duty cycle or effective max switching frequency during transient, to determine the max inductor current range for each phase, I need to take all these factors into consideration in worst case, as it is helpful to inductor optimization. 

    If you have such waveforms tested in bench, or a simple sketch map, it is good to me. If not, it doesn't matter and I can help it myself.

  • 0 in reply to user4811888
    TI__Mastermind 24805 points

    Hello,

     We don't have the waveforms you're asking; all useful waveforms for application have been included in its datasheet. 

     For what your concern, as long as the 700mV min dropout voltage met; there is no issue at all for any load change in specs and phases reconfiguration for load sharing will be handled automatically by the device inside control circuit. 

    Thanks!

    Phil

  • 0 in reply to Phil Yi40
    Intellectual 530 points

    Okay, thanks for your kind reply.