• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 63 subscribers
  • Views 1016 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.

How to calculate R(threshold) and R(sense) for LM9061

Mohamed Emara
Prodigy 20 points
Other Parts Discussed in Thread: LM9061, LM25069

Hello,

I am using LM9061 with a power MOSFET (mftr. part number: IPT004N03L. Digi-Key: http://www.digikey.com/product-detail/en/IPT004N03LATMA1/IPT004N03LATMA1CT-ND/4571877). The MOSFET has a resistance of 0.4 mOhm and the voltage supply is 12V. I was wondering how to calculate the threshold and sense resistances to be connected between pin 1 and pin 2 of LM9061, respectively. I checked the datasheet (http://www.ti.com/lit/ds/symlink/lm9061.pdf) but couldn't find any helpful information regarding R(threshold) and R(sense).

Thank you for your time.

Regards,

Mohamed Emara

Flextronics

  • 0
    TI__Genius 12621 points

    Hi Mohamed,

    We have many newer devices than the LM9061 which have higher accuracy and/or advanced protection features. Depending on your load current needs, we also have devices with an integrated FET which we call eFuse and provide a small solution size and may reduce overall BOM cost.
    http://www.ti.com/lsds/ti/power-management/integrated-fet-devices-products.page

    To answer your question regarding the LM9061, the relevant equations are on page 14, 15 and 16.

    Iload (max) = Vds / Rds on (min)

    and Vds (max) = Vref * Rthr / Rref - Isense*Rsense + Vos

    and Rsense is recommended to be less than or equal to Rthreshold (1kohm should be adequate - see top of page 16).

    Iref = Vref / Rref = ~80uA

    So to solve for Rthr, it would be Rthr = (Iload * Rds on + Isense * Rsense - Vos)/Iref

    = (Iload * Rds on + 10uA * 1kohm +/- 10mV)/ 80uA

    Thanks!
    Alex

    Edit:

    Based on the FET you selected, I assume this is a high power application?

    For high power, some of the newer devices we would recommend are the TPS2471x series and the LM25069:

     

    TPS2471x:

    and we have a design tool available under Tools and Software:

     

    LM25069:

    Design Tool:

     

  • 0 in reply to Alex Triano
    Prodigy 20 points
    Thank you for your reply, Alex! This was very helpful. I will also consider your recommendations for the current and future designs.