• State TI Thinks Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 64 subscribers
  • Views 776 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.

LM5166: Current limit Specification in PFM mode

Yoshwa
Expert 4050 points
Part Number: LM5166

Our customer has designed a PFM mode application of 50V input and 12V 0.45A output.

HIS, RT and ILIM pins are pulled down to GND directly.

He measured coil current to be going up to about 2A at the peak point of the ripple current on about a 0.3A load condition.

The ripple current are repeated with two and three burst pulses

The current limit value is specified up to 1375mA (MAX).

What does this mean?

  • 0
    TI__Mastermind 25590 points
    Yoshwa,

    Can you share waveforms, schematic, and layout? It sounds like you're getting current overshoot or maybe your inductor is not sized properly. It's hard to say for sure without more information.

    -Sam
  • 0
    TI__Guru 73102 points
    Yoshwa,

    What is the inductance value? Note that there is a current response time of 80ns once the current exceeds the nominal ILIM value. This is specified in section 7.3.5 of the datasheet. The current overshoot will be more evident at high VIN. Please use the LM5166 quickstart tool to assist with component selection for your design - this is available for download in the LM5166 product folder. Also, another option is to use the LM5166 in COT mode.

    Regards,
    Tim
  • 0 in reply to Timothy Hegarty
    TI__Expert 4050 points

    Tim-sann

    Thanks for your comment.

    Customer used WEBENCH tool and designed his circuit for VIN=35V to 60V, VOUT=12V IOUT=0.47A frequency=600kHz.

    Inductor and capacitor values are as follow,

    L=15uH  Isat=1.9A  RDC=89mΩ

    Cin=4.4uF  Cout=44uF

    An inductor current phot is as attached, where VIN=50V, IOUT=about 300mA.

    Green is SW voltage and Red is inductor current.

    LM5166 VIN=50V Iout=0.3A.pdf

     

  • 0 in reply to Yoshwa
    TI__Guru 73102 points
    Yoshwa-san,

    The inductance is too low. If you fill out the design in the LM5166 Excel quickstart calculator, you will see the cell for inductance is indicated in red.

    For 60V in to 12Vout, 27uH is the lowest inductance allowed to maintain peak inductor current less than 1.6A. See equation 29 in the datasheet for clarification.

    Regards,
    Tim