• State
  • Locked Locked
  • Replies 1 reply
  • Subscribers 62 subscribers
  • Views 513 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

LM9061 threshold calculation for low current

Gerardo Vecchiato
Prodigy 20 points

I have been struggling with calculating the threshold and sense resistor values for use with an FDS5351 n-channel mosfet from fairchild.  I would like for the over current to kick in at around 2A to 2.5A maximum.  I have tried several values but no luck.  Any help would help.

  • 0
    TI__Intellectual 2010 points
    Hi Gerardo,


    Imax= [(Iref*Rthresh)-(Isense*Rsense)+Voffset]/Rds(on).

    And from the datasheet:
    • Rref should be 15.4k, therefore Iref=1.25V/15.4k=81uA
    • Rthresh must be greater than Rsense
    • Isense(max)=10uA
    • Voffset = +/- 10mV
    • Rds(on) @ 10V Vgs = 35mOhm

    With Rthresh=1k and Rsense=750, and assuming Isense = 5uA and Voffset=0, the current limit would be 2.2A.

    Rthresh may need to be tuned from there depending on the actual offset voltage of the internal comparator, the 10mV swing makes a big difference