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LM43603 not working correctly

carlos.ramos14
Prodigy 200 points
Other Parts Discussed in Thread: LM43603

Hello everyone,

I currently did a design featuring the LM43603 Converter. The application is to convert 24VDC to 5VDC @ 1.3 Amps for a Beaglebone Black power supply. The problem I am having is when I connect the power supply to the BBB when booting, the power supply drops the voltage to 2.1V and the BBB shuts down. I did this design following the WEBENCH app but I don't know what's wrong with the design.

Best regards.

Carlos Ramos

  • 0
    TI__Genius 16025 points

    Hi Carlos,

    Can we take a look at your schematic and PCB layout? I have a feeling that there is either a short on your power supply output or a mismatch between the power supply and the Beagle Bone. 

    A good way to test the power supply on its own is to place a 10W power resistor with a 3.84ohm rating on the output and see if the power supply is still regulating at 5V. If it is not, then check that 24V power supply can indeed supply at least 0.5 Amps of current. 

    Once I look at your schematics, I can help you better.

    Thanks,

    Anston

  • 0 in reply to Anston Lobo
    Prodigy 200 points

    Thanks for the reply,

    I placed a dynamic load at the LM43603 output and still does the same behaviour, starts at 5V and then drops to 2.1V. Attached are the requested files.

  • 0 in reply to carlos.ramos14
    Prodigy 200 points

    I forgot to include the schematic!

    LM43604 PCB LAYOUT.pdf
  • 0 in reply to carlos.ramos14
    TI__Genius 16025 points

    Hi Carlos,

    I've isolated the problem to be the layout of your board. There is a feature called thermal relief that causes the pads for the inductor, capacitors and diodes to be traces instead of solid polygons. Please disable thermal relief to fully make use of the copper area.

    Please bulk up power heavy traces such as VIN, GND and SW. These traces carry a large load and having a thin trace will cause a lot of parasitics to throw off the part or even damage it. Especially for variable loads such as beagle bones it is important to have wide traces as far as possible to handle transients.

    Make sure your inductor RMS rating is at least 2.5A. Also make sure your input and output capacitors have twice the voltage rating required.

    If none of these recommendations work, replace the IC and try again. Let me know how it works out.

    Thanks,

    Anston