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LDC2112: LDC2112 EMI trace and coil shielding

Part Number: LDC2112


Since we have a issue that when our MCU IC internal power is DCDC mode(switching frequency is 8MHz), it radiation impact our LDC2112 coil(design resonant frequency is ~13MHz) that the LDC2112 base raw data become 100~200(when at LDO mode, the base raw data is 3~4)

We can add ferrite sheet between MCU and coil to solve this issue but it increase cost 

By your SNOA962 "EMI Considerations for Inductive Sensing" document, section 2.1, seems add a ground pattern also can mask radiation

Since our FPC is three layer and our coil is at first and second layer, we can add ground pattern at third layer to isolate radiation

So I have some questions as below~~

1. For 2.1.1 trace shielding, ground or COM shielding which one is better? Or both is OK?

2. For Coil shielding, question as below

   1. Our coil pattern is racetrack, is it also ok use figure 1 shielding type? The shielding pattern also need symmetry with coil center?

   2. About below shielding, a. what is shielding pattern trace width and gap ? b. what is outside ground trace width? c. what is the gap between coil and outside ground trace? d. what is the mean of "Connection at a single point away from sensor coil"?

3. About figure 2 there is 3 shielding pattern, which one is better?

Thank you~~


  • Poki,

    Thank you for your inquiry and your interest in TI products.

    According to the app note and device data sheet, use the COM pin for the LDC2112.

    The app note advises shield traces to be orthogonal to the sensor traces to minimize parasitic capacitance.
    The importance of that will depend on your system and design requirements. For example, if the parasitic capacitance is too high, it may be difficult to adjust your circuit to the desired resonant frequency, or achieve the desired sensor Q.

    The shield's geometry, symmetry and placement should support the goals of minimizing EMI and minimizing the sensor's parasitic capacitance. Any of the three examples in Figure 2 may do this, depending on the design and placement of the coil and the shield, and your design goals.

    The phrase "Connection at a single point away from sensor coil" refers to the solid traces connecting the shield to ground/COM  being routed in a way that does not place them under the sensor coil. 

    Please let me know if you have any more questions.