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DRV425: Several questions of "DRV425 Bus Bar Application Magnetic Field Calculator.xlsx"

Hirotaka Matsumoto
Guru 27585 points
Part Number: DRV425

Hi all

Would you mind if we ask "DRV425 Bus Bar Application Magnetic Field Calculator.xlsx"?

<Question1>
The default Sensor Spacing value is 2.0mm.
Does it mean that total thickness is 2.0mm(PCB thichness 1.6mm and device sensor location =0.4mm)?


<Question2>
In case of vertical setting of the device at center circle of the Bus Bar, it seems that it recommends to use two devices.
Does "DRV425 Bus Bar Application Magnetic Field Calculator.xlsx" mean that it evaluates one device?
The customer would like to configure with two devices. 

<Question3>
In case of using commercial voltage, should we set "Current" which is instantaneous value after direct current conversion?
Should we consider configuring Peak current?

Kind regards,

Hirotaka Matsumoto

  • 0
    TI__Mastermind 32260 points

    Hello Hirotaka,

    Thank you for coming to the forum for your engineering questions.

    Question1

    The 2mm spacing was done as a possible solution.  The sensor spacing from the bottom of the DRV425 is 0.35mm.  So to calculate the sensor spacing from a PCB thickness of 1.6mm we would need to add 0.35 mm twice to consider the spacing between two DRV425 devices.  This would be a total of 2.3 mm.  This is exactly what was calculated in Figure 2.  For my vertical hole calculation for the TI Design, ±100A Bus Bar Current Sensor using Open-Loop Fluxgate Sensors Reference Design Evaluation Assembly

    Question 2.

    Everything is done with two devices.  An evaluation can be done quickly using our current TI Design that is order-able.  We also have more information in our Bus Bar Theory of Operation

    Question 3

    This is dependent of the application.  If you need higher resolution at the lower currents and you do not need information at the peak current you can saturate the DRV425 without an issues.  If you need the measurements at the peak currents then you must design to that current.  My ideal situation is to design for 1mT at each DRV425 for the maximum current you are attempting to measure before saturation.  Note when using this analog circuit you will be limited and the full scale range of each of the DRV425 is not 2mT.  This is discussed in detail in the  Bus Bar Theory of Operation section 4.1.5.

    .

  • 0 in reply to Javier Contreras4
    Guru 27585 points

    Javier  san

    Thank you so much for your coperation!

    If you have some knowleadge about follows, could you share us it?
    -When the magnetic flux density changes from 20mT(saturation area) to 2mT, how much will be recovery time and residual hysteresis? 
    We assume that the recovery time is quickly as our assumption.

    Kind regards,

    Hirotaka Matsumoto 

  • 0 in reply to Hirotaka Matsumoto
    TI__Mastermind 32260 points

    Hirotaka,

    I do not have the capability of testing 20mT to 2mT but I was able to test from ~4.75mT to 0mT and I have provided a screen shot below.  The yellow trace is labeled current as it is a measurement of current that is generating the magnetic field.  Vout is the DRV425 Vout referenced to GND.  I have a 5V supply and Vref is set to 2.5V.  Therefore at zero magnetic field Vout =2.5V.  You can see the response is approximately 100uS from coming out of saturation.  Also this is with Rshunt at 100 Ω and the part device saturates at a lower field and also decrease the bandwidth but I do not believe it will change the time to get out of saturation. 

    Please let me know if you have further questions.