LDC0851: Stacked Coil

Janine Lin

Part Number: LDC0851
Other Parts Discussed in Thread: LDC1312, LDC1612, LDC1614

Hello T.I. team

Under LDC0851 Stacked coil design considerations, there is a recommended keep out distance between coil and PCB, as shown in the figure.

My question is what is the recommended distance for this stacked rectagular coil? as shown in the figure. This PCB layout drawing was taken under LDC Reference COILS USER'S GUIDE.

And what does it mean by Q in the graph? What is the relationship with Q and Frequency? How to get a longer sensing distance? For LDC0851 EVM, can sense what kind of material (target conductor)?

Thank you for the answer.

Best Regards,

Janine Lin

over 6 years ago

0 Janine Lin over 6 years ago

Expert 2190 points

We already purchased the LDC0851 EVM and want to understand more about these module.

0 Clancy Soehren over 6 years ago

TI__Mastermind 23810 points

Janine,

The keepout region should be 1/2 of the width of the coil (the shortest measurement across the coil).

Q = Rp*Sqrt(C/L)

The LC circuit acts as a bandpass filter around its resonant frequency. A higher Q factor means that the filter is more narrowband, which is desirable. You can look up Q factor relating to bandpass filters to learn more about it.

0 Janine Lin over 6 years ago in reply to Clancy Soehren

Expert 2190 points

Dear Clancy,

Does this rectangular coil can use in LDC0851 evm? May i know what is the sensing distance if the Lsense coil close to metal conductor?

Thank you.

0 Clancy Soehren over 6 years ago in reply to Janine Lin

TI__Mastermind 23810 points

As I mentioned earlier, you need either a stacked coil or a side-by-side coil for the LDC0851. If this drawing is of a stacked coil, then it could work. For your sensing distance question, please refer to the LDC0851 stacked coil app note:

www.ti.com/.../snoa982

0 Janine Lin over 5 years ago in reply to Clancy Soehren

Expert 2190 points

Dear Clancy,

What is the maximum inductance for coil?
Thank you

0 Janine Lin over 5 years ago in reply to Clancy Soehren

Expert 2190 points

Dear Clancy,

It says that using 8 layer stacked coil will meet the minimum inductance of the LDC0851 sensor drive current.

Does it mean, the switching distance will decrease?

0 Vaibhav Garg10 over 5 years ago in reply to Janine Lin

TI__Intellectual 1020 points

Hello Janine,

In account of the holidays, our responses will be delayed.

Regards,

Vaibhav Garg

0 Clancy Soehren over 5 years ago in reply to Janine Lin

TI__Mastermind 23810 points

You can look at figures 9 and 10 in the datasheet to see the acceptable design space. The maximum drive current, minimum inductance, and minimum capacitance are all specified.

If you are space constrained, then sometimes you need four layers to meet the minimum inductance. You can use our LDC tools calculator to estimate inductance for various coil sizes, space widths (dependent on PCB manufacturing capabilities), and number of layers.

www.ti.com/.../slyc137

0 Janine Lin over 5 years ago in reply to Clancy Soehren

Expert 2190 points

Thank you for the reply. We tested our own coil by attaching it to evm, but the result the sensing range is much lesser. Our company product size is small, we use smaller coil size but this LDC0851

is applicable for bigger sensor coil size.

0 Janine Lin over 5 years ago in reply to Janine Lin

Expert 2190 points

Would you recommend us what kind of inductive sensor IC can use smaller coil size ? Thank u

0 Clancy Soehren over 5 years ago in reply to Janine Lin

TI__Mastermind 23810 points

Janine,

You can get more range with the other LDC devices because they have a higher resolution. The LDC0851 is just an inductive switch. Did you already try adjusting the ADJ code to adjust your range?

The other LDC devices that will provide more range are LDC1312 and LDC1612.

0 Janine Lin over 5 years ago in reply to Clancy Soehren

Expert 2190 points

Thank u for the recommendation. Yes, I already adjust the ADJ code but the range is only 5.6mm. But after changing the R4 to 0 ohm, the maximum range becomes 8mm.

0 Clancy Soehren over 5 years ago in reply to Janine Lin

TI__Mastermind 23810 points

Janine,

That is as good as you are going to get with that size of coil. You will need to look at other devices or use larger coils if you need more sensing range.

0 Janine Lin over 5 years ago in reply to Clancy Soehren

Expert 2190 points

The one you suggest the LDC1614, how far is the sensing range( for proximity sensing)? Does the IC sensor also need larger coils?

Does LDC1614 can be used for smaller coils? We purchased the evm and try if we can use this device to our product. We would like to understand more

the functions of this IC.

0 Clancy Soehren over 5 years ago in reply to Janine Lin

TI__Mastermind 23810 points

You can detect up to a distance of about twice the diameter of the coil (along its shortest dimension) with the LDC161x. It can use small coils as well. You can use the LDC tools spreadsheet to experiment with potential designs.

0 Janine Lin over 5 years ago in reply to Clancy Soehren

Expert 2190 points

If our coil diameter is 11mm x 6mm, does it mean its sensing range(proximity sensing) is 12mm with the LDC1614? Our company's product is small and it's using smaller coils.

Below, coils from TI. Are these coils is for LDC1614?

0 Clancy Soehren over 5 years ago in reply to Janine Lin

TI__Mastermind 23810 points

That will approximately be the maximum sensing distance. Also, that coil board should be able to work with the LDC161x.

0 Janine Lin over 5 years ago in reply to Clancy Soehren

Expert 2190 points

Thank you very much Clancy. We are also also using rectangular and racetrack coil for our design.

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LDC0851: Stacked Coil