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LM5117: How to implement a pulsed constant current supply at various CC levels (10mA, 1A and 3.5A)

Part Number: LM5117

I have similar design question related to one post such as LM5117: How to implement a pulsed constant current supply for driving laser diodes? - Power management forum - Power management - TI E2E support forums

If I want to 'dynamically' control the output current at 3 different levels as listed for example.   What would be the simplest way of doing so?  Would something like this work?

What if I have options to add parallel resistors to the RFBbottom resistor and controlled the FETs with GPIOs from a MCU (for example).   By default, the FETs are off and say I have output current set at 10mA.  If I want 1A, I just turn on the next resistor and if I want 3.5A, I just turn on the next resistor.  Would this work?

thank you.

  • Hello Long

    I haven't tested the configuration on the bench, but I think it should work well.

    - Eric Lee ( Applications Engineering) 

  • Thanks Eric.  How would you approach this design if it were you?  Is there another TI solution that would be a better fit for this?  

    1) Wide input range, up to 36V

    2) Configurable CC @ 10mA, 1A and 3.5A.

  • Hello Long 

    Your approach make sense to me. I just have a small worry about the low IOUT regulation and the wide IOUT regulation range. Please consider these items when designing your board. 

    1. Please make it sure to not trigger peak current limit at 3.5A CC. Consider 10-15% overshoot.
    2. CM works well only in CCM. Please make it sure the converter works in CCM at 10mA CC . If you cannot select a proper inductor, then please consider the configuration in the figure 1 of SNVA829 App Note at  https://www.ti.com/lit/an/snva829/snva829.pdf 
    3. Coss of the Q4 pull down switch should be small. The source connection of Q4 should be connected to a clean AGND

    - Eric Lee ( Applications Engineering) 

  • Hello
    I am closing this thread since I have not heard from you for sometime.
    If you are still trying to resolve the issue, please feel free to open a new thread or reopen this thread.
    Thanks
    - Eric Lee (Applications Engineering)