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.

LM5161-Q1: ON time in current limit mode

Part Number: LM5161-Q1

Hi,

We got a question from the customer about LM5161-Q1.
Could you help us?

[Question]
How is determined ON time in current limit mode? They want to culcurate the output current in current limit mode.

They assume the ON time is determined by equation (3) and the period is until the inductor current reaches the current limit threshold. Is this our understanding correct?

Best Regards,
tateo

  • Hello Tateo,

    If high side current exceeds ILIM(HS) ~ 1.65 A, the MOSFET is turned off after TRES ~ 100ns. This is a separate circuit from the normal on timer so does not depend on the ON timer. In the functional block diagram, this circuit is shown as the current limit comparator.

    Your engineer is correct when writing that if current is below ILIM(HS) equation 3 does determine on time. Once above ILIM(HS) there is only a ~100ns delay before the HS FET is turned off.

    Regards, Robert
  • Hi, Thank you for your support. We got additional question from customer. Could you confirm this?

    If the IC operate with under the following condition, how does the IC determine the off time?

    - Condition -
    1. Peak inductor current hits the Ilim(hs)
    2. High side SW turns OFF after Tres=100ns
    3. The IC staies OFF while Toff(cl)
    4. Vfb is above 2V even if off time passed Toff(cl)
    5. Will the high side SW stay OFF? or Will the high side SW turn ON?

    Best Regards,
    tateo

  • Hello Tateo,

    The SW will stay off until FB is below 2 V even if the toff timer has been activated. That way transition from over current to soft short is smooth.

    Regards, Robert