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Original question:

LDC0851: increasing the sensing distance of a stacked design sensor

LDC0851: Stacked coil configuration

Tim Waters
Prodigy 20 points
Part Number: LDC0851

In reference to a stack coil design; given a four layer board @0.62mils (1.5748mm) using 1oz copper for all layers; what is the recommended distance between coil layers so as to the greatest distance between the Lref and Lsense, where Lref is on 1 set of layers and Lsense being on the other?

  • 0
    TI__Mastermind 18545 points

    Hello, 

    In general, the larger the distance you can have between the sense and ref coils, the better your sensing range will be. 

    The LDC0851 Stacked Coil Design Considerations app note goes into more detail about the impact of this separation. 

    Best Regards, 

    Justin Beigel

  • 0 in reply to Justin Beigel
    Prodigy 20 points

    Understood. I guess if I rephrase the question. Is there a minimum distance between coil layers of the same coil so the distance between Lref and Lsense can be at max distance in a standard 62mil PCB board. This question would also apply to a design that would require using a flex, separating Lref and Lsense with a dialectic piece of material such as foam.  

  • 0 in reply to Tim Waters
    TI__Mastermind 18545 points

    Hello, 

    There isn't necessarily a minimum distance between layers of the same coil. It could depend on the manufacturing capabilities of the PCB manufacturer but as long as your coil design stays within the supported bounds of the LDC0851, then you can make it as thin as you need. Decreasing the layer height between the coil layers will impact the mutual inductance of the coil so it is important to take that into consideration when determining if the coil design will work with the LDC0851. Section 2.3 of the Sensor Design for Inductive Sensing Applications Using LDC app note talks more about how the multiple layers affect the inductance of the coil. Additionally, if you haven't seen it already, we have the LDC-CALCULATOR-TOOLS excel spreadsheet available to help calculate the impact of changes like layer height or number of turns. There is even an LDC0851 tab of the spreadsheet to help determine feasibility of the coil design. I will note that the distance calculation of that tab is based on side-by-side coils and you should expect slightly decreased range for a stacked coil. 

    Best Regards, 
    Justin 

  • +1 in reply to Justin Beigel
    Prodigy 20 points

    Thanks for the help.