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Original question:

LM5146: ILIM RC Circuit and Current Limit Issue

LM5146: Constant Current Mode

Benjamin Luo
Prodigy 20 points
Part Number: LM5146
Other Parts Discussed in Thread: LM5190, LM5148

Tool/software:

Hi,

I am confused by the current limiting functionalities of the LM5146 DC/DC Buck Converter.


From what I can understand, there are two modes of over-current protection offered by LM5146: hiccup mode in which the buck converter shuts off after a prolonged over-current event, and the cycle-by-cycle current-limiting feature in which the duty cycle is shortened in the event of an over-current event as shown in the diagram above. I interpret the latter as a constant-current mode feature and would like to use that to charge a battery. However, my design seems to go into hiccup mode every time without trying to limit the current when connected to a battery. Is the LM5146 able to act as a CC/CV device with only a voltage feedback loop?

Regards,
Benjamin

  • 0
    TI__Genius 11595 points

    Hi Benjamin,

    For battery charging - you can consider using https://www.ti.com/product/LM5190-Q1 (Automotive Grade)/ https://www.ti.com/product/LM5190 (Industrial Grade) - this device incorporates CC-CV regulation directly. 

    We have implemented CC/CV using LM5146 internally - however, the performance of current mode control devices for CC/CV is always better. However, the easiest solution here is to check out the LM5190 which will make your design simple!

    Thanks,

    best Regards,

    Taru

  • 0 in reply to Taru Kapoor
    Prodigy 20 points

    Hi Taru,

    Thanks for the recommendation. I will take a look at that in my next design.

    But my question remains. Is the LM5146 able to limit its current to that set by the ILIM before hiccup occurs, akin to constant current mode? If so, what might be the cause of a hiccup being triggered without current limiting being observed?

    Thanks,
    Benjamin

  • 0 in reply to Taru Kapoor
    Prodigy 20 points

    Hi Taru,

    Thanks for the recommendation. I will take a look at that in my next design.

    But my question remains. Is the LM5146 able to limit its current to that set by the ILIM before hiccup occurs, akin to constant current mode? If so, what might be the cause of a hiccup being triggered without current limiting being observed?

    Thanks,
    Benjamin

  • 0 in reply to Benjamin Luo
    TI__Genius 11595 points

    Hi Benjamin,

    Benjamin Luo said:
    Is the LM5146 able to limit its current to that set by the ILIM before hiccup occurs, akin to constant current mode?

    The current is limited before hiccup occurs by reducing the on time - however, the device keeps track of how long this occurs - if it happens for 128 consecutive cycle - the device will go into hiccup mode (if the overcurrent condition is not removed) and do a soft start sequence - hence this is not a true constant current mode. 

    Benjamin Luo said:
    If so, what might be the cause of a hiccup being triggered without current limiting being observed?

    Can you share your waveforms that you may have captured - I am not sure if this will happen - Meanwhile, I saw in the other post where my colleague Tim had recommended you to change the ILIM setpoint - have you done that? 

    Thanks,

    Best Regards,

    Taru

  • 0 in reply to Taru Kapoor
    TI__Genius 11595 points

    Hi Benjamin,

    Please see some additional resources to help you here:
    https://www.ti.com/lit/an/snvaa85/snvaa85.pdf (Although this is for LM5148/9)

    We also created a break-out board to be connected with the LM5146EVM to work as a CC/CV design. Please see report below:
    LM5146 Test Result.pdf

    Thanks,

    Best Regards,

    Taru