• State
  • Locked Locked
  • Replies 4 replies
  • Subscribers 64 subscribers
  • Views 3060 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

LM5145: Understanding about the ILIM pin function?

Lin_Charles
Expert 4260 points
Part Number: LM5145

In the datasheet p24 and p16, the ILIM comparator is different. Which one is correct? From p24, I think this method is to limit the peak current, not valley current.

U_ILIM=ILIM×R_ILIM -U_Q2_on

When circuit is in overload situation, U_Q2_on  will be higher, and U_ILIM will be lower. If the U_ILIM is lower than zero, then a hiccup happened. So the lowest point in ILIM is ILpeak×R_ILIM -U_Q2_on . So it is to limit the peak current, am I right？ And can you give me some me some waveform test on the ILIM pin to help me to understand the function of this pin?

When the OCP happen, why the ramp voltage will be higher than before? I can not understand the waveform below better, can you explain it for me? Thanks a lot!

  • 0
    TI__Mastermind 23845 points
    Hi,

    We have received your question. I'll see if i can contact the application engineer for this device

    Thanks
    -Arief
  • 0
    TI__Guru 73402 points

    Hi Charles,

    The LM5145 senses current during the conduction time of the low-side MOSFET and thus provides valley current limiting. The output of the current limit comparator differs only with respect to its polarity that is provided to the subsequent block in these too figures. A current limit state is detected when the voltage drop across the low-side MOSFET (or current sense resistor if connected) exceeds the current limit threshold set by the resistor attached to the ILIM pin.

    Regards,

    Tim

  • 0 in reply to Timothy Hegarty
    TI__Expert 4260 points

    But when the LSFET is on, the current will cross the RILIM from GND to the inductance. And the voltage on RILIM will increase, seen from the above picture. And we should let the lowest point of the curve to be higher than zero, which is the peak current of IL. Am I right?

  • 0 in reply to Lin_Charles
    TI__Guru 73402 points

    Hi Charles,

     

    The current is sensed at the end of the low-side MOSFET conduction interval (based on the clock pulse just prior to high-side MOSFET turn on). Thus, it’s valley current sensing.

     

    Regards,

    Tim