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LM3409-Q1: About Laser Overdriving Issue

Kim Yangrae
Prodigy 70 points
Part Number: LM3409-Q1
Other Parts Discussed in Thread: LM3409

Tool/software:

Hello. There have been cases where lasers that were stably outputting brightness when driven in certain locations (process lines) suddenly become overdriven. Among them, I saw a comment in a previous thread that said that if T_ON is not longer than 211ns, the window is not found and it continues to be recognized as T_ON.

DLP4620SQ1EVM: Increasing the optical power cause Lasers of different colors to turn on. - DLP products forum - DLP®︎ products - TI E2E support forums

The Sync Pulse Width in the DLPC230 Control Program is 3code and the period at this time is 100ns. Since the recommended T_ON time should be over 211ns, I think it should be over 7code (230ns), but in this case, the current seems to be higher than before as the T_ON time increases. 
Simply re-tune the current by re-tuning the DAC Limit. However, I'm setting the Sync period to 30 code (1.03us) and matching it to the Sync below 1MHz specified in the Datasheet, but I'm afraid that as the T_On time increases, more power is consumed, so I need to set a lower period than the recommended 1MHz.

The point is, 1) if I change the Sync Pulse Width to 7 code (0.23us), will the above overdriving case disappear? 2) if I change the Sync Pulse Width to 7 code (0.23us) and the Sync period to 30 code (1.03us), will the operation be ok? Please let me know.

  • 0
    TI__Expert 5720 points

    Hello, 

    I am assigning this to the correct department as this team handles automotive LED drivers, such as the LM3409, and not the DLPC230.

    Best,
    Daniel

  • 0
    TI__Expert 3405 points

    Hello,

    I think as we already mentioned this issue may not be resolvable using this driver scheme.  I might suggest that we have a discussion off line about options.

    Jason

  • 0 in reply to Jason Thompson
    Prodigy 70 points

    This is a separate question from making a new board, but rather a question about utilizing modules made from existing boards. If what was said in the previous thread is the problem, then conversely, I understand that there is no problem if Ton is over 211ns. However, in this case, it is expected to be brighter than before, so the point of the question is whether the sync period affects stability.

  • 0 in reply to Kim Yangrae
    TI__Expert 3405 points

    Hi Kim, 

    I think the overdriving case is dependent on the overall feedback loop and current levels switching from one laser to the next laser.  For example, if the red laser is 1A and the Green laser is 3 A, then when the switching between these colors quickly there can be overshoot and undershoot.  The sync frequency helps to some extent, but the larger impact is due to manage the extra energy in the circuit that needs to be quickly sourced or dumped.  This is why in the laser driving circuit, the current level is fixed to avoid these big up/down level of current that we use in the LED circuit.

    Jason

  • 0 in reply to Jason Thompson
    TI__Intellectual 2550 points

    Hello Mr. Kim,

    If you think having online meeting would be helpful, let us arrange it. Please let me know your opinion.

    .

    Regards,

    Victor Park