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LM43603 Power Regulator Problem

Chris Simpson
Prodigy 10 points
Other Parts Discussed in Thread: LM43603

Hi,

I'm attempting to manufacture 29-31V to 5V @ 0.5A power regulator using the LM43603 synchronous step-down voltage converter. I designed the circuit around the WEBENCH simulation, verified by the design equations, and constructed a PCB board where the power regulator is being used as part of a larger transmitter circuit. The schematic and PCB layout are shown below:

Due to strict size constraints, there wasn't space on the PCB to use the pad, but the ground is connected and there aren't any short-circuits. The resistor connected to RT was left open circuit to set default frequency, but a footprint was added to give the option to change. However, when testing out the manufactured board, I received the following output:

I've checked the connections and I've attempted all obvious solutions. The regulator does not appear to be switching. I would really appreciate any assistance with this matter.

Thanks in advance,

Chris

  • 0
    TI__Guru 57555 points

    Unfortunately, you can not omit the DAP connection.  It is required  for proper electrical operation as well as thermal.  Also, some of you power traces, such as SW are too narrow.  I would suggest that you copy the layout found in the data sheet as a starting point; especially the power and ground connections.  The guidelines given in the data sheet are important to achieve a good working design.  The user guide for this device also shows the layer stack-up for our evaluation board.  These documents can be found on the product folder for this device.  If you like I can send you an EVM that you can use as a starting point and check out your design on a clean board.