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TMCS1100 (EVM)

Jeroen van Bentem
Prodigy 20 points

Hello,

I forward my question to you on the advice of:

Jonathan Navor
Texas Instruments | Customer Support Center

I bought an evaluation board through mouser. When I connect the A3 evaluation module (power only and no current through the sensor), I already have an error / change of 22mV at the output just by holding it upside down. It doesn't matter where I do this. Office, workshop, etc.

With the A4 variant, this deviation is 40mV.

It looks like an offset is introduced by just turning it upside down.

shielding does not seem to have any effect.

What is going wrong here?

Regards,

Jeroen van Bentem

(Netherlands)

  • 0
    TI__Mastermind 26335 points

    Hello Jeroen,

    Thanks for considering to use Texas Instruments.  I suspect this has something to do with the external fields.  Can you provide a diagram of how you are shielding it?  If the shielding is inadequate, the earth's magnetic field could be contributing the offset.  Using the formula, (Earth's Magnetic Field)/(Magnetic Coupling Factor)*Sensitivity=60mT/(1.1mT/A)*(Sensitivity mV/A), I calculate ~10mV for A3 and ~20mV for A4.  The cumulative difference from flipping the chip upside down and reversing the polarity of the b-field to the hall sensor would be double those values.  Other external magnetic sources such as nearby high current wires/traces could also influence the offset.

    Yet another possibility could be something with the current density on the board itself. Did you change connectors or place the connectors on the bottom layer of the board?  Typically if it is affecting the distribution of current to the input pins you would probably see a gain or sensitivity error.

  • 0
    Prodigy 20 points
    Hello Patrick,

    I only connected your evaluation board. Therminals for the current carrying path have been removed.

    I placed the entire print in a metal box as a shield.

    I don't see any change in the behavior described earlier.
    What should the shielding on your evaluation module look like to overcome this phenomenon?

    Can I assume that if the setup is physically constant, the offset that I observe as a result of the setup is constant.?

    Met vriendelijke groet, kind regards,

    Jeroen van Bentem

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  • 0 in reply to Jeroen van Bentem
    TI__Mastermind 26335 points

    Hello,

    What material is your shield made of?  For the shield in my lab, we use concentric mu metal cylinders, like in the image below. The cylinders are normally grey, but we painted these for some thermal experiments.  If you search for a Gauss chamber, you may find cylinders similar to ours.  These admittedly are quite bulky.  I think you might be able get mu metal sheets and create your own smaller version of these.

    I did some tests in my lab and I think the Earth's magnetic field is a little less strong in my region of the world.  For my tests I used a TMCS1101A4B on an EVM (1101 is the same silicon as the 1100, except the reference bias is provided internally to midsupply.)  Powered to 5V, I saw the output shift 32mV when I flipped the board upside down.  Inside my chamber, I did see significantly smaller change in output (1-4mV) as long as the board was held in the center of the inner chamber.

    I think without mu metal shielding, the output shift will change if your setup moves or is re-oriented.