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DRV5055: Magnetic Sensing Proximity Tool - Weird Output Readings

Rio Schad
Prodigy 10 points
Part Number: DRV5055

Have a few questions in regards to a TI calculator I am using,  Magnetic Sensing Proximity Tool. When I place the south side of the magnet facing the DUT (sliding from X =  -10mm to +10mm), the Z component (Bz) appears to read positive rather than negative (which I confirmed should be negative by using the DRV5055EVM I have in the lab).Also, the output voltage appears to be 2.5V instead of VCC/2 when at 0mT (also confirmed in lab using the DRV5055EVM). Am I missing something here? Specific part no is DRV5055A3QDBZR.

  • 0
    Prodigy 10 points

    I have also tried changing the package type but get the same result. The TO-92 is what I’m testing with on the dev board, while the SOT-23 (DRV5055A3QDBZR) is what we are using. I ran the sim using bot South Facing DUT and North Facing DUT with same result. Also tried using Head On for Magnet Movement, using both North and South Facing DUT. Overall, the B field magnitude is still positive. Shouldn't the overall magnetic field magnitude (sum of the components) be negative?

  • 0 in reply to Rio Schad
    TI__Prodigy 320 points

    Hello Rio,
    Thank you for alerting us of this issue. You have identified some bugs in our tool.

    You are correct in thinking that low field or no field when the magnet is far from the device, should result in an output of Vcc/2, which is 3.3V/2=1.65V in your case. A south field facing the device should yield an output greater than 1.65V, while a north field facing the device should yield and output less than 1.65V.

    While the Z component has the wrong polarity the magnitude should be correct. Does this match what you are measuring on the DRV5055EVM?

    At the moment we are looking into fixing these bugs, we will provide you with an update when this is fixed.

  • 0 in reply to Christen Waite
    Prodigy 10 points

    Hi Christen,

    Thanks for the update. I tried testing again using the DRV5055EVM and the included N35 magnet as a reference. The magnitudes I see using the magnetic proximity tool vs the EVM are different still. See red annotation. annotation in pic below.

  • 0 in reply to Rio Schad
    TI__Prodigy 320 points

    Thank you for confirming this information for me.

    We are looking deeper into these bugs and I will provide you with an update when it is fixed.

  • 0 in reply to Rio Schad
    TI__Mastermind 26335 points

    Hello Rio,

    Im working on fixing the various bugs in the tool.  I need a few more details to determine the extent of the bugs.

    For both TO-92 and SOT-23, the tool orients the device such that Bz corresponds to the Hall-element sensing direction. Based on the information provided and the device magnetic response (shown below), I would expect your device on the EVM to measure +7 to +8 mT when the South side is facing the DRV5055A3LPG.

    Additionally, when you measured your -8mT can you confirm that it was centered with respect to the Hall element situated at the origin of the x and y lines below?  If it was offset by a few mm you might get significantly different measurements.  Also does 4.75mm correspond to your magnet radius or diameter?