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LMR51430: Voltage drops after putting up the load

Keshav Aggarwal
Prodigy 20 points
Part Number: LMR51430
Other Parts Discussed in Thread: LMR14030, , LMR33640

Hello There,
I'm looking to port a LMR14030 design to LMR51430X for12-36v Input to 9v Output conversion. I'm facing some issues with the initial testing.
With no load, multimeter correctly reads 9v at output. But after putting up the load of just 0.5A, voltage drops to around 8.3V.
Also, while on load, the output voltage doesn't stay stable (7-8.3v) if I vary the Input(12-30v).

Any help is appreciated. I'm referring the below design.

Regards,

KA

  • 0
    TI__Guru 68775 points

    Hi Keshav,

    Thank you for reaching out.  Please note that the LMR514430 is a synchronous buck namely it employs an internal low side FET as the rectifier to replace the regular freewheeling diode, while the LMR14030 is a nonsync buck which does not have the low side FET integrated, hence you will need to employ a freewheeling diode in order to make it work. 

    Hope this clarifies.

    Best Regards,

    Youhao

  • 0 in reply to Youhao Xi
    Prodigy 20 points

    Hello ,
    I think you have misunderstood the problem. I'm facing an issue with LMR51430 not LMR14030.
    I know LMR14030 design uses a freewheeling diode. Also, that diode isn't required in LMR51430 design as per the datasheet. 

  • 0 in reply to Keshav Aggarwal
    TI__Guru 68775 points

    Hi Keshav,

    Sorry for misunderstanding.  What do you exactly mean by "port"?  Using the same PCB but rewire the connection?  Instead of the Webench schematic, may I bother you to share your own schematic and maybe your PCB photo picture?

    Thanks,

    Youhao

  • 0 in reply to Youhao Xi
    Prodigy 20 points

    Hello Youhao,
    By port I meant, I rewired the connections on a General Purpose PCB but soldered the IC on an adapter PCB.
    The schematic is exactly same as per the Webench. I'm facing issue with this specific part number.

    I also tried other part numbers LMR14030, LMR33640. They are working fine.

    Regards,

    Keshav Aggarwal

  • 0 in reply to Keshav Aggarwal
    TI__Guru 68775 points

    Hi Keshav,

    Since you verified with LMR14030 and LMR33640, I don't see why LMR51430 cannot work.  Sorry to ask but could your show me a photo picture of your GP PCB with the adapter PCB? 

    Thanks,

    Youhao