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LP87524P-Q1: Using only three bucks

MaN
Prodigy 30 points
Part Number: LP87524P-Q1

Hi!

We have a project were we've used LP87524PRNFRQ1 configured in the following way:
Buck0: 0V85
Buck1: 0V9
Buck2: 2V1
Buck3: 1V8

Currently we no longer have the need for 0V9 rail on Buck1 output of the LP87524PRNFRQ1 and so we would like to remove all components related to that output. We would like to keep the LP87524PRNFRQ1 because of other reasons.

Is it OK to leave the pins SW_B1, FB_B1, VINB1, EN1 floating or should we connect them in some other way?

Is there something else we need to take care in HW design to support 3/4 outputs?

Is there any documentation reference to this state?

Best regards,

  • 0
    TI__Intellectual 2101 points

    Hi,

    we don't have detailed documentation over this state, but there is a thread with a question very similar to yours.

    Overall:

    • VinB1 would need to stay connected.
    • FB_B1 is best to leave grounded.
    • EN1 is OK to leave floating, but EN1_PD will need to keep the pulldown resistors active. They are active by default, but removing this setting will leave the logic of this pin undefined.
    • SW_B1 is OK to leave the floating so long as the regulator is disabled by I2C. If it is active, a SC fault will occur as described in the E2E thread I linked.

    Nonetheless, as the thread explains, we do not have any verification/tests over the long term effects of this design. Due to this risk, we don't recommend removing the components.

    We also have a design checklist, found here, for reference.

    Best,

    David Martinez

  • 0 in reply to David Martinez
    Prodigy 30 points

    Hi David,

    thank you very much for a prompt response. We will follow you advice and not use the LP87524P-Q1 in this way. Do you have some recommendations for buck ICs with three outputs which would suit our application? Not considering the ones from the same family which have 2-phase outputs.

    Best regards,

  • 0 in reply to MaN
    TI__Intellectual 2101 points

    Hi,

    I'll need some more information to give a recommendation:

    1) Is the application automotive?

    2) What are the current requirements for each rail? 

    Feel free to list any other requirement your application has.

    Best,

    David Martinez

  • 0 in reply to David Martinez
    Prodigy 30 points

    Hi,

    1) Application is automotive.

    2) Current requirements per rail:

    0V85 - 2A

    2V1  - 2A

    1V8 - 2A

    Br,

  • 0 in reply to MaN
    TI__Intellectual 2101 points

    Hi,

    Unfortunately we do not have a single-chip solution for these requirements. The closest match I found was the TPS65653-Q1 which has 2 regulators. An extra DC/DC converter will be needed for the 0V85 rail.

    Best,

    David Martinez