• State
  • Locked Locked
  • Replies 7 replies
  • Subscribers 47 subscribers
  • Views 2776 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.

DRV401-Q1: how to choose a proper magnetic circuit for DRV401 ?

jie qian
Prodigy 245 points
Part Number: DRV401-Q1
Other Parts Discussed in Thread: DRV401, DRV421

Hi! all!

i want to develop a current sensor sample (which was used in motor control system, have high precision  ) with DRV401 ,  so a proper magnetic circuit should be chosen .

please see the figure as below, the material of probe core was FeNi alloy(80%Ni), it has high permeability. the size and airgap as below, and the number of  turns on the core was 300.

from the datasheet, i know a voltage 5V was applied on the probe circuit (please see the second figure, it was from the datasheet ) ,when the voltage 5V was applied on it , the probe

core will reach saturation in several μs, then the voltage will reverse and make the probe core to reach saturation on reverse direction, so if  there is no current to be test,  the probe coils will get

a 50% pwm. but in my magnetic circuit ,  i found a big problem:

my question 1 was : when the 5V drive circuit applied on the probe core (size 5mmX1mmX1mm ,1j80 material,and 300 turns copper wire on it ), it will not reach saturation at all . please see my simulation (use ansys maxwell applied ±5V) result as figure 3,  the B at probe core should be 0.8T when saturated, but in my simulation, the result was about 0.037T. but in the datasheet ,when the current was 28mA, the probe core will be saturated .so why it can not get saturation and how can i get a proper probe core size?which size the probe core should be ?do you have any suggestions?

my question 2 was: the figure 4, it was from the datasheet.  when probe core got saturation, i think the current on coils should be (5V)/(55Ω+55Ω+18Ω)=39mA, but the document said it was 28mA when probe core got saturation, it conflict, and i am confused ,how to understand? can you give some explain?

thank you very much!

  • 0
    TI__Mastermind 31240 points

    Hello jie qian,

    I am looking into this for you and need to get some information from some colleagues.  In the meantime could you send me your ANSYS files.  If you would not like to post them on this forum please let me know.

  • 0 in reply to Javier Contreras4
    Prodigy 245 points

    OK,thank you.Looking forward to your reply.simulation.zip

  • 0 in reply to Javier Contreras4
    Prodigy 245 points
    Hello! Javier,
    do you have any results?
    thanks!
    Best Regard!
  • 0 in reply to jie qian
    TI__Mastermind 31240 points

    Hello Jie Qian,

    Q1) I believe the probe is too thick and large in order to get saturated.  I am having issues simulating and I may need to adjust some things or redraw in order to simulate your design.  The smaller the probe the easier it will get saturated.  Once I get the simulation working on my system I will see what I come up with.

    Q2)The typical value is with many variation accounted for such as variation from device to device.  Your design should work at the minimum of 22mA and also at the maximum of 34mA.  Please note you need to account for the impedance of your probe coil and the probe material shifting.

    Suggestion.  Have you looked into the DRV421.  This device already has the probe integrated into the device.  The design would be much easier to implement.  There is information on the website for the DRV421 but I can also help you with that design as well.

  • 0 in reply to Javier Contreras4
    Prodigy 245 points
    Hello Javier:
    I looked into the DRV421, it was not used in automotive industry and the accuracy was ±2% , i want the accuracy should be less than ±1%. So the DRV401 is more proper.
    best regards!
  • 0 in reply to jie qian
    TI__Mastermind 31240 points

    Hello Jie Qian,

    The 2% is only the reference accuracy and when measuring the voltage output referenced to this pin as shown in the typical application circuit in page 1 you will not have an issue with this 2% accuracy of the reference.  If you cannot make a differential measurement you can always add an external reference to get the accuracy you required.  We also have DRV421 System Parameter Calculator which you can see the calculations of some of the errors and how they are impacted by several input parameters.  We also have a TI design, TIPD196,  that uses the DRV421 to measure current and is able to meet your 1% requirement.  The measured accuracy was -0.153% error uncalibrated and -0.0195% with calibration.

  • 0 in reply to Javier Contreras4
    Prodigy 245 points

    Hello Javier,

    Thank you very much for your suggestions, but i still want to solve the probe core not saturated  problem about the DRV401 application. and i change the probe core size to 0.4mm(length)X0.1mm (wide)X5mm(height). in my simulation it was saturated in the center point but still not saturated in the lower point, the entire probe core should be saturated? or just some parts? and why?. and the size of  probe core should be smaller ?and how about your simulation results?Thank you.

    Best regard!