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LP8758-B0: Hoe to connection if not used 1-channel

Yuto Sakai
Mastermind 6100 points
Part Number: LP8758-B0
Other Parts Discussed in Thread: LP8758, LP8758-E0

Hi,

When using Buck 0, 1, 2 and making Buck 3 unused,
how do you recommend connecting the VIN_B3, SW_B3, and FB_B3 pins?
Is there a problem with the following connections?
Are there any recommended settings for registers?
-------------------
VIN - B3 = VIN
SW_B3 = floating
FB_B3 = GND
-------------------

Or, if it is LP8758-B0 version, can not I make 1-core unused?

Best Regards,
Yuto Sakai

  • 0
    TI__Genius 13850 points

    Hi Sakai-san,

    For LP8758-B0 it is not possible to disable one of the cores. BUCK cores 1,2 and 3 are controlled by the master core BUCK0 and therefore the master core will override any other settings for slave cores than current limit.

    Best regards,

    Jari Niemelä

  • 0 in reply to Jari Niemela13
    Mastermind 6100 points

    Hi Jari-san,

    Thank you for your reply.
    In the BIT0 section of 8.6.1.3 BUCK 0_CTRL1 of the data sheet P.30, it is written as follows.

    I understood that this will force 3-phase operation at the time of 3 phase operation configuration.
    What does the three phase configuration refer to in this case?

    Our customers's condition is Iout = 5 to 6 A,
    and they are considering reducing the circuit area by reducing external circuits (inductors and capacitors) for 1 or 2 channels.

    I'd like to know if peripheral circuits can be reduced.
    If possible, I would like to know processing of pins and necessary register settings too.

    Best Regards,
    Yuto Sakai

  • 0 in reply to Yuto Sakai
    TI__Genius 13850 points

    Hi Sakai-san,

    LP8758-B0 is 4-phase configuration. For 3-three phase configuration we have not released catalog device.

    3-phase means that BUCK0 ,1 and 2 outputs are connected together and BUCK3 is alone. So configuration is actually 3+1

    See this document link also for the reference about different LP8758 phase configurations.

    If you would like get more information about these different configurations please contact your local TI sales team for further support.

    Best regards,

    Jari Niemelä

  • 0 in reply to Jari Niemela13
    Mastermind 6100 points

    Hi Jari-san,

    I'm sorry for late reply.
    I understand that forced to multi-phase operation described in BUCK 0 _ CTRL 1 is forced to operate with the number of phases corresponding to each LP 8758 series, is it correct? (Does "3 phases in the 3-phase configuration" refer to LP8758-C0?)

    Then, what kind of behavior does LP8758-B0 operate with "Automatic phase addition and shedding" of Buck 0_FPWM_MP=0?

    Also, when using the LP8758-B0, does the inductor require the equivalent product for 4ch?
    Please tell me if you have any hints on reducing the circuit area.

    Best Regards,
    Yuto Sakai

  • 0 in reply to Yuto Sakai
    Mastermind 6100 points

    Hi,

    I am still expecting your response regarding my post.
    Please tell me if you have any questions.

    Best Regards,
    Yuto Sakai

  • 0 in reply to Yuto Sakai
    TI__Genius 13850 points

    Hi Sakai-san,

    I apologize my late reply.

    Yes, 3-phase configuration refers to LP8758-Cx version.

    Automatic phase adding and shedding is a functionality of the device to measure load current from each phase and based on that add or shed active phases to maintain best efficiency and load current delivery.

    For the LP8758-E0 buck3 inductor, the device is intended to be used with similar inductors on all bucks but there could be a chance to change different inductor for the buck3 if inductance and load current needed to start-up and shutdown the buck are fulfilled. But this is highly experimental and I expect customer to validate correct functionality on their application.

    Best regards,

    Jari Niemelä

  • 0 in reply to Jari Niemela13
    Mastermind 6100 points
    Hi Jari-san,

    Thank you for your reply.
    I'm sorry, is it okay for you to advise about inductors B0 version?
    It is B0 version used by our customers.

    Best regards,
    Yuto Sakai
  • 0 in reply to Yuto Sakai
    TI__Genius 13850 points

    Hi Sakai-san,

    We have a couple of good inductor options in LP8758-B0 datasheet. But since bucks design requirements are validated under certain conditions we are stick to those. I mean inductor value and inductance variation is specified to be between certain limits.

    From Murata I found some 330nH inductor which might be possible to use. DFE201612E-R33M has over 4A current rating and inductance seems pretty good over load current range.

    I read again your original post and noticed that customer loading is static 5-6 A total. This means that all 4 bucks will be active at the same time and share load current equally. This forces also to use similar inductors on every buck to make all bucks similar. Also up to 6A static load it is recommended to use -B0 device which can operate in 4ph mode.

    Best regards,

    Jari Niemelä