SNOA930C March   2015  – May 2021 LDC0851 , LDC1001 , LDC1001-Q1 , LDC1041 , LDC1051 , LDC1101 , LDC1312 , LDC1312-Q1 , LDC1314 , LDC1314-Q1 , LDC1612 , LDC1612-Q1 , LDC1614 , LDC1614-Q1 , LDC2112 , LDC2114 , LDC3114 , LDC3114-Q1

 

  1.   Trademarks
  2. 1The Sensor
    1. 1.1 Sensor Frequency
    2. 1.2 RS and RP
      1. 1.2.1 AC Resistance
      2. 1.2.2 Skin Effect
  3. 2Inductor Characteristics
    1. 2.1 Inductor Shape
      1. 2.1.1 Example Uses of Different Inductor Shapes
    2. 2.2 Number of Turns
    3. 2.3 Multiple Layers
      1. 2.3.1 Mutual Inductance of Coils in Series
      2. 2.3.2 Multi-Layer Parallel Inductor
      3. 2.3.3 Temperature Compensation
    4. 2.4 Inductor Size
    5. 2.5 Self-Resonance Frequency
      1. 2.5.1 Measurement of SRF
      2. 2.5.2 Techniques to Improve SRF for Wire-wound Inductors
  4. 3Capacitor Characteristics
    1. 3.1 Capacitor RS, Q, and SRF
    2. 3.2 Effect of Parasitic Capacitance
      1. 3.2.1 Recommended Capacitor Values
    3. 3.3 Capacitor Placement
  5. 4Physical Coil Design
    1. 4.1 Example Design Procedure Using WEBENCH
      1. 4.1.1 General Design Sequence
    2. 4.2 PCB Layout Recommendations
      1. 4.2.1 Minimize Conductors Near Sensor
      2. 4.2.2 Sensor Vias and Other Techniques for PCBs
  6. 5Summary
  7. 6References
  8. 7Revision History

4.2.2 Sensor Vias and Other Techniques for PCBs

  • Inner vias must be placed close to the traces and not in the absolute center of the inductor — this reduces the parasitic resistance.
  • Keep the inner 30% of the sensor area unwound for most applications, but for inductive metal button replacement, place as many turns as possible.
  • The sensor capacitor must be placed as close as possible to the sensor to minimize the RS of the traces. Note that this rule does not apply to LDC0851, LDC2112, LDC2114, and LDC3114 devices. For these devices, place the sensor capacitor close to the corresponding device pin.
  • Use thicker traces between the inductor and capacitor when possible. Typically 10 mil (0.25 mm) is sufficient.
  • Do not use a ferrite bead as a sensor inductor — it does not generate a magnetic field effective for LDC applications.