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LM3643: start-up/ramp-down for ~ 1ms on LED current

Robert Eschbach
Expert 6695 points
Part Number: LM3643
Other Parts Discussed in Thread: LM3644

My customer has asked: 

In one of our products we are using LM3643 LED driver.

I was looking at the datasheet and noticed the current “ramp up/down” for ~ 1ms on LED current.

[see attached]

 Could you, please, have an application engineer contact me to discuss this characteristic?

I need to understand this characteristic in relation to different modes of operation.

Ultimately, I would need to turn on/off the LEDs really fast (<50us).

Are there any other LED drivers similar to LM3643 with fast turn on/off feature that could be used?

 I just need to know if fast turn on/off times are achievable with these types of LED drivers.LM3643 Question.pptx

  • 0
    TI__Mastermind 28655 points

    Read Part number incorrect.

  • 0
    TI__Mastermind 22745 points

    Hi Robert,

         Sorry for the late response, we actually have another device LM3644 which can support fast turn on/off with IR mode. You can refer to the LM3644 datasheet Page 15 as below:

    "8.3.3 IR Mode
    In IR Mode, the target LED current is equal to the value stored in the LED1/2 Flash Brightness Registers. When
    IR mode is enabled (setting M1, M0 to '01'), the boost converter turns on and set the output equal to the input
    (pass-mode). At this point, toggling the STROBE pin enables and disables the LED1/2 current sources (if
    enabled). The strobe pin can only be set to be Level sensitive, meaning all timing of the IR pulse is externally
    controlled. In IR Mode, the current sources do not ramp the LED outputs to the target. The current transitions
    immediately from off to on and then on to off."

    Best Regards

    Sean

  • 0
    TI__Mastermind 22745 points
    Hi Robert,
    LM3643 also support IR mode which can support fast turn on/off. Please refer to LM3643 datasheet page 12 as below:
    "In IR Mode, the target LED current is equal to the value stored in the LED1/2 Flash Brightness Registers. When
    IR mode is enabled (setting M1, M0 to '01'), the boost converter turns on and set the output equal to the input
    (pass-mode). At this point, toggling the STROBE pin enables and disables the LED1/2 current sources (if
    enabled). The strobe pin can only be set to be Level sensitive, meaning all timing of the IR pulse is externally
    controlled. In IR Mode, the current sources do not ramp the LED outputs to the target. The current transitions
    immediately from off to on and then on to off."