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Original question:

Should I pour a ground plane under a hall-effect switch?

DRV5056: Should I avoid copper pours when sensing a magnet located on the opposite side of the PCB of my hall effect sensor?

Ruben Osorio Lopez
Prodigy 10 points
Part Number: DRV5056
Other Parts Discussed in Thread: TMAG5273

Tool/software:

Hello!

I have a design using multiple DRV5056-A3 hall effect sensor in the SOT-23 package. There is a magnet on the other side of the PCB moving perpendicular to the PCB.

I was wondering if it is a good idea to clear up any copper pours that would be in-between the sensor and the magnet. This is currently a 4-layer PCB and it would likely have a couple of ground layers and perhaps a 3.3V layer in between the sensor and the magnet.

The only resource I found related to this was in this forum here (https://e2e.ti.com/support/sensors-group/sensors/f/sensors-forum/441749/should-i-pour-a-ground-plane-under-a-hall-effect-switch), however in their case the sensor and magnet were both on the same side of the PCB. They do mention a 12% different in magnetic field, which if consistent, it seems quite relevant for my case.


Anyone has any experience or advice on the pros/cons of trying to cut the copper layers underneath the sensors?

Cheers!

Ruben.

  • +1
    TI__Mastermind 19840 points

    Ruben,

    Copper is a diamagnetic material.  It may experience some repulsion by the magnet in cases where there is a very strong field changing rapidly. In most cases the diamagnetism of copper will be negligible and un-noticed.  Given the description of your application I do not expect a significant impact.

    If you do not need to copper pours beneath the sensor, then it is probably okay to remove them as long as it does not have any negative effort on your system's performance. If you need shielding from noisy signals or the good return path for emissions requirements, then I would probably leave the pour in place. 

    I attempted to run my own experiment using TMAG5273 (3D Hall-effect Sensor) where I set a permanent magnet next to the sensor on the table and inserted and removed a 2-layer PCB with ground pours on both layers between the magnet and sensor.  I saw no measurable change in my measurement of the field in all 3 axes except for when I physically disturbed either the sensor PCB or the magnet with my handheld PCB.

    Thanks,

    Scott

  • 0 in reply to Scott Bryson
    Prodigy 10 points

    I see, thanks Scott! I'll likely leave the copper pours then.

    Thanks again for your answer!

    Ruben.