When customers are designing proximity-switch applications using inductive sensing devices like the LDC0851 switch, they often ask me how to design a coil for a given switching distance. Today, I want to show you how to use TI’s new WEBENCH® tool to make these calculations, provide computer aided design (CAD) files for coil layout, and then build and test a prototype for a proximity application in three easy steps.
I will use the example of an open/close lid application from a previous blog post. A simplified diagram is provided below for reference.
Figure 1: Lid open and close detection with LDC0851
To access the WEBENCH tool, go to the LDC0851 product page and navigate to the on/off sensing tool on the right, as shown in Figure 2. Alternatively, simply type www.ti.com/ldc0851webench into your browser.
Figure 2: Inductive sensing WEBENCH tool for proximity-switch applications
Figure 3: Select a design
Figure 4: Open design
b. Click CAD File Export, shown on the bottom right of Figure 4, and choose from a variety of CAD tools to open the design, as shown in Figure 5.
Figure 5: CAD export tools
c. Download and open the file. Add any finishing touches to the PCB, as shown in Figure 6.
Figure 6: Open up the coil layout and add final touches
d. Finally, the design is ready to be packaged up and sent for quote.
Prototype and testing phase
Once you receive your coil design, you can connect it to one of our prototyping tools such as the LDC0851EVM and begin prototyping, as shown in Figure 7.
Figure 7: Build design and prototype
To test the switching distance I connected a flat metal target to a linear position motor and swept the target metal back and forth over our prototype to find the switching distance versus the adjustment (ADJ) code. Figure 8 shows that I achieved a switching distance of 3mm for an ADJ setting of 1. A simple way to set this ADJ value is to use Table 1 from the LDC0851 datasheet. For an ADJ setting of 1 it is recommended to use a resistor divider of 49.9 kΩ and 3.32 kΩ which are common resistor values.
Figure 8: Switching distance curve
This design is ready for use in our lid open/close applications and meets the original requirements of 3mm switching distance with our specified PCB constraints.
Now you can say that proximity switch applications can be as easy as 1, 2, 3 with WEBENCH® on/off inductive designer. What are your experiences designing proximity-switch applications? Log in to comment below.
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