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: Questions regarding the DRV425 magnetic sensor - Saturation

Part Number: DRV425

Hi Team,

I've some technical questions regarding the DRV425 magnetic sensor.

Questions regarding DRV425 sensor saturation:

  1. I understand that when the DRV425 is exposed to a magnetic field above 3.6mT it becomes saturated. I understand that when the DRV425 is saturated, it will output an offset voltage even in the absence of a magnetic field. Except for this offset voltage, does the response of the sensor is linear?

Is it true that the DRV425 response:

In normal state: Vout = k * magnetic field

In saturation state: Vout =  k * magnetic field + saturation offset ?

  1. Is it possible to restore the normal state by a degaussing procedure? If yes, what procedure is recommended?

 

Thanks,

Shlomi

  • Hello Shlomi,

    Thank you for using the fourm. 

    So I think there may be two quesitons here and I will address both of them.  One is how it reacts when it is saturated and then how does it react after saturation. 

    First the saturation can happen at a lower field and it is dependent on many factors (Rshunt, VDD, Vref, Temperature).  Please see the DRV425 system parameter calculator.  There is a range calculator and normally we say it can saturate at 2mT.

    Most of the time when the DRV425 saturates it will reach a rail as it attempts to compensate the magnetic field internally.  If the magnetic field transition is too fast it could blind the sensor that it cannot determine the correct direction and my go to the incorrect rail as expected.  This normally does not happen as usually the field transitions and the DRV425 can determine the correct direction of compensation needed.

    After saturation the DRV425 can experience some hysteresis and is typically 1.4µT.    This is just the material of the sensing unit.  Most of our data shows it is able to recover well.  The fluxgate sensor is already acting in a degassing procedure as it is always going into and out of saturation and that is why the material recovers pretty well. 

    For those instances that it does not that I have not seen there you could attempt to degauss the material but I would do it with the part off. 

    Could you share what level of field you are seeing and saturating and for the duration?  What level of hysteresis are you seeing?  Could you be magnetizing something on you PCB that is magnetic and it holds the field.  Are you using and DRV425EVM for this verification?

  • Hi,

    My questions about saturation state refer to the following description from the data sheet:

     

    "For fields that exceed the measurement range of the DRV425 by 1.6 mT, the fluxgate is permanently saturated and the ERROR pin is pulled low. In this condition, the fluxgate sensor does not provide a valid output value and, therefore, the output VOUT of the DRV425 must be ignored."

     

    I hope to have the answers for this type of saturation.

     

    Thanks,

    Shlomi

     

  • Hello Shlomi,

    The 1.6mT above the compensated level  is when you will get the error flag will be active.  During this point is when the fluxgate sensor is completely saturated.  At this point the output of the DRV425 cannot determine the valid direction of the field.  

    Compensation level can also be seen in the  DRV425 system parameter calculator under "Maximum Compensation Field" in the "Calculated System Parameters" section.  As described above this value can change based on your input parameters.

    The example in the datasheet is for a compensation for 2mT.  Therefore the error flag will not be active till you get above 3.6mT = 2mT +1.6mT.  Yes this saturates the sensor but after returning to fields below 2mT it will continue to function with a possible magnetic hysteresis and that would be a typical value of 1.4µT.

    For this example any time the field is above 3.6mT you cannot trust the output of the DRV425.  This means field directions as well.  So do not expect the output to saturate in the correct direction in this condition.

  • Hi Javier,

     

    I understand that after the sensor has been exposed to a magnetic field above 3.6mT and saturated, when the magnetic field returns to normal values (below 2mT), it operates as usual.

     

    Since in the data sheet it is written that the saturation condition is permanent, I just want to verify that this saturation condition is NOT permanent and for normal magnetic field values (below 2mT) the sensor returns to operate normally after it was saturated.

     

    Thanks,

    Shlomi

  • Shlomi,

    I will update the datasheet on the next revision but I assure you it will not permanently saturate.  As soon as you remove the field it will return to normal operation.  You can validate this easily by placing a magnetic next to the DRV425EVM and then removing it.  A magnet will very likely produce a field much greater than the 3.6mT required to saturate and you can also monitor the Error pin.   Please be aware you could still see a typical magnetic hysteresis of 1.4µT.

  • Hi Javier,

     

    Thanks for fast response. It is very good news that the sensor will not permanently saturate.

     

    Thanks,

     

    Shlomi

     

  • Shlomi,

    If this resolves your issue please indicate by clicking on this resolved my issue.