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

2.3 Multiple Layers

For PCB inductors, there is a maximum number of turns that can be placed in a given diameter. If the overall inductance of the sensor is still too low, adding an additional inductor on another layer increases the total inductance. Note that these additional inductors need to be physically aligned, as shown in Figure 2-6, so that the magnetic fields positively add. Electrically, the inductors are connected in series. In general, with a PCB spiral inductor, a second layer is generally available because most PCBs are at least two layers.

When routing multiple layers, it is important to alternate the rotation of the coils – if the top layer is routed with a clockwise rotation, the next layer down must have a counter-clockwise rotation. While this may seem counter-intuitive, this physical arrangement is needed in order to keep the current rotating in a constant direction.

GUID-81D27E4C-799D-4C56-9D44-8DAB977B86DF-low.gifFigure 2-6 Multiple Layer Inductor Construction (Series)
GUID-AF67FFC8-215B-4223-AFC8-FC2396F04CE2-low.gifFigure 2-7 Simplified Electrical Model of Four-Layer Series Sensor (Ignoring RP)