• State
  • Locked Locked
  • Replies 2 replies
  • Subscribers 30 subscribers
  • Views 221 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.

DRV425: Over-the-trace current sensing

Jason Silver
Prodigy 75 points
Part Number: DRV425

If the DRV425 is to be used for sensing current through a PCB traced located beneath the device package, how should the thermal pad be connected? 

  • 0
    TI__Mastermind 32290 points

    Hello Jason,

    You can connect it to GND as the solder is non-magnetic.  I have an image below of a board we did that was used for a similar measurement.

    I would ask a few other questions if you have though about when measuring the current using this method.  Have you simulated the results from geometries of your PCB?  I have used FEMM before which a free software.

    How will you deal with external magnetic fields?  For example other current sources, earths magnetic fields?  ( I normally use two DRV425 and measure a delta between the two)  Are you calibrating to account for PCB manufacturing variation.  Thickness of trance and width of the current carrying conductor.  The DRV425 will also have some variation on the internal location of sensor relative to the outside of the package.  All these may not matter but understanding that you will need to look into this.  Please let me know if I can assist in any of this or explain further.

  • 0 in reply to Javier Contreras4
    TI__Mastermind 32290 points

    Jason,

    I just realized you may have wanted to run the trace at the location of the pad.  You can place solder-mask and not connect thermal pad.  The risk is that the solder mask does not have any issues and shorts to the thermal pad to you current trace.  The vias I believe would be the location of most concern..  I am not sure if this will work as you would need to tell me how much current you are trying to measure.  

    I have to verify that we can leave the thermal pad floating but I do not think it will be an issue.

    All the other issues above still apply.