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LM5123-Q1: schematic review

Che Wen Yeh
Intellectual 900 points
Part Number: LM5123-Q1

Tool/software:

Hi teams,

Please help to review LM5123-Q1 schematic. Thanks.

Vin : 9~16V  Vout : 16V  Imax : 14A

5661.LM5123_Excel_Quickstart_Calculator_for_Boost_Controller_Design.xlsx

  • 0
    TI__Mastermind 19585 points

    Hello Che Wen,

    Thanks for reaching out to us via e2e.

    We are very busy these days, so please allow for one or two days to get a reply.

    Thanks and regards
    Harry

  • 0 in reply to Harry Hofner
    Intellectual 900 points

    Looking forward to your reply.

  • 0 in reply to Che Wen Yeh
    TI__Mastermind 19585 points

    Hello Che Wen,

    Iam sorry for the delay.

    I will get back to you tomorrow.

    Thanks and regards
    Harry

  • +1 in reply to Harry Hofner
    TI__Mastermind 19585 points

    Hello Che Wen,

    Thanks for your patience.

    The chosen switching frequency of 250kHz is quite low.
    This is not really an issue, but it means that you will need the big overall output capacitance which is shown in your schematic.

    The topology of the compensation network is wrong.
    C4409 needs to be directly connected to the COMP pin.
    When using the other components in the schematic, R4421 should be increased to 80k or even 100k.

    The current sense resistor R4420 of 1Milliohm would set the peak current to 60A, which is way too high.
    We would recommend 2 Milliohm instead (maximum 1.5 Milliohm)

    We would also recommend adding the following footprints:
    A filter in the current sense line (CSP/CSN) But please keep the resistance in the CSP line at 0 Ohm.
    Gate resistors
    Maybe also a snubber.
    So, these parts can be added / modified, when necessary.

    There should be no resistor in series with the VCC capacitor. Please remove R 4424 / keep it at 0 Ohm.

    In the layout, please create a separate AGND island, where all sensitive signals are connected.
    The only connection between AGND and PGND should be from the AGND pin via the exposed pad to the PGND pin.

    These separate ground domains are not reflected in the schematic.

    Please follow the layout design rules that are shown in the datasheet, and do not use any thermal relief connections for the high current components nor for the VCC and the HB capacitor.


    All information in this correspondence and in any related correspondence is provided “AS IS” and “with all faults” and is subject to TI’s Important Notice: http://www.ti.com/corp/docs/legal/important-notice.shtml

    Thanks and regards
    Harry