• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 63 subscribers
  • Views 867 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

WEBENCH® Tools/LM3409HV: Driver gives out a whine and does not work

HPB
Expert 1350 points
Part Number: LM3409HV

Tool/software: WEBENCH® Design Tools

I'm using the LM3409HV to drive about 12 LEDs (6 parallel strip with 2 in series in each strip). Each LED consumes about 300mA. When I turn on the circuit, I hear a high pitched whine from the board. Also the LEDs do not light up. I used Webench to configure this for a 4A output at 5.2V. The schematic is shown here. I added an external voltage reference that supplies the Vadj (1.24V) through a divider network. Any idea what am I missing here?

  • 0
    TI__Mastermind 25500 points

    Hello,

    I'm assuming you have already checked for cold/missing solder joints and you have checked all of your components? If so the first thing I would do is make sure the DAP is soldered down (that can be difficult and it can cause problems if it isn't). I am also curious about the EN pin. Are you pulling that high actively or leaving it floating? If it is floating that could cause the part to turn on and off very quickly and could cause audible noise.

    If your DAP is down and the EN pin is pulled high then we would need to dig a bit deeper. In that case scope shots of the switch node (FET, L, and D connection) would be useful as would the BOM and layout. Very often with switchers the layout is a problem. The layout guidelines in the datasheet need to be followed closely. Let me know. Thanks,

    Regards,

    Clint

  • 0 in reply to Clinton Jensen
    Expert 1350 points

    It seems to be working now. I guess one of the joints was a cold solder joint. I'm guessing "DAP" is the chip? The EN pin is actually a 3-pin header. I wanted to eventually adjust output current using a PWM from a microcontroller. However, when the EN pin is floating, all the LEDs are ON. Only when I ground it, does the device turn OFF.

  • 0 in reply to Clinton Jensen
    Expert 1350 points
    I guess I should have a pull-down resistor on the EN pin?
  • 0 in reply to HPB
    TI__Mastermind 25500 points

    Hello,

    For default on operation you would want a pull-up resistor from EN to VIN. Then you could apply a PWM signal to EN for dimming. You can "OR" it through a diode if you are concerned the pull-up will interfere with your PWM signal in any way.

    Regards,

    Clint