• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 64 subscribers
  • Views 471 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

LM3434 works only in "burst mode"

Frank Seyfferth
Prodigy 20 points

I build a board with a LM3434, similar to the eval-board.

It should drive 1 LED with max 30A.

The switching frequency is 600kHz.

The driver works for about 30us then it stops and start again with a frequency of 10kHz.

The device is enabled and no dimming is active.

I make some modifications to the eval-board and this is running with 30A.

I need some hints what could be wrong and where to look.

  • 0
    TI__Genius 13700 points
    Hello Frank,

    Can you post a copy of your schematic and a copy of the scope shot showing the 10kHz beat and information on where you are probing your circuit?

    Do you see these issues if you lower your switching frequency or lower your LED drive current a little bit?
  • 0
    TI__Mastermind 25500 points
    Without further information I can tell you the vast majority of issues with these designs is the layout. 30A current generates a ton of switching noise and if you are not very careful (you route the sense traces near the switches, switch node, inductor, don't use sufficient ground/power planes, etc...) you can cause this type of behavior. The EVM took significant effort to get it clean enough for high currents, I would recommend trying to duplicate the layout of it. Also consider inductance to the LED, if you are using long leads between the converter and the LED you can generate significant noise as well. You may need to use and output capacitor (if no PWM dimming) or a snubber at the output (if PWM dimming) to prevent issues.
  • 0 in reply to Clinton Jensen
    TI__Mastermind 25500 points
    One last thing, I would suggest lowering the switching frequency for currents that high. It's also possible you are running out of drive current and you will for sure be hurting efficiency and creating excess noise. I would reduce it to maybe 300kHz or so.