LDC5072-Q1: Offset error in SIN/COS output.

Nimish Kothari

Part Number: LDC5072-Q1

Tool/software:

Hello,

We have successfully interfaced the LDC5072-Q1 inductive position sensor with the metallic (Aluminium) target and as suggested by the
In LDC5072_Sensor_Designer software, we followed the steps to get proper sinusoidal sin/cos output.

However, we faced an offset issue in SIN/COS output (Amplitude difference). We tried Automatic Gain Control and Manual Gain Control by adjusting the voltage across the AGC_EN pin through the resistor divider.
However, the results are the same. I've attached the schematic of the actual hardware and the results for your reference. As you can see in the results image the phase difference between SIN/COS is correct but the amplitude of both outputs is different and it varies with the Air gap between the sensor and target. (Yellow is SIN+ and Blue is COS+ with respect to Ground).

Please suggest or guide us to overcome this issue.

Thanks and regards
Prasanna Pandit
Aproposdrive, Pune.

19 days ago

0 Nimish Kothari 19 days ago

Prodigy 10 points

I have added 4 (18pF/50V) capacitors for each coil as we can see in the Schematic and also pulled up/pulled down with a 10K resistor for all output, but I didn't see any difference by doing that. By adjusting the Air gap between the target and sensor PCB I got the following results.
How can I remove this offset..?

0 John Miller - Sensing 18 days ago in reply to Nimish Kothari

TI__Mastermind 35565 points

Nimish,

Are you using your own custom layout for the PCB, or the one provided by the sensor design tool?
What do the interconnects & traces between the coils and the LDC look like?

Regards,
John

0 Nimish Kothari 18 days ago in reply to John Miller - Sensing

Prodigy 10 points

Hello John,

I hope you are doing well.

1) I have used the layout provided by the software (LDC5072 sensor designer tool) for our application which is 50x20 mm.
2) The Coil and LDC are on the same PCB (4 layers) and the coil is interconnected to another coil using via. I just added pin headers for debugging between them. I'll attach an image for your reference.

Thanks and regards,
Prasanna Pandit.

0 John Miller - Sensing 17 days ago in reply to Nimish Kothari

TI__Mastermind 35565 points

Prasanna,

Have any changes been made to the board compared to the layout generated by the tool?
What is meant by "the coil is interconnected to another coil using via"?

regards,

John

0 Nimish Kothari 17 days ago in reply to John Miller - Sensing

Prodigy 10 points

Hello John,

No, changes have been made to the actual board compared to the layout generated by the design tool.
The coil is interconnected across the PCB's 4 layers, with one-half of the coil located on the top layer and the other half on the bottom layer. This interconnection is achieved using vias to maintain the continuity and functionality of the coil across layers.

0 John Miller - Sensing 14 days ago in reply to Nimish Kothari

TI__Mastermind 35565 points

Nimish,

Thanks for the clarification.
I will look into this and update this thread by COB tomorrow.

Regards,
John

0 John Miller - Sensing 13 days ago in reply to John Miller - Sensing

TI__Mastermind 35565 points

Nimish,

For any exciter frequency, the offset is sensitive to the trace paths from the receive coils' outputs to the device input pins.
The exciter frequency and trace parasitics also contribute.
If your application allows it, you could try tweaking the exciter frequency to see if it affects offset.

We are working on guidance for layout rules-of-thumb to optimize offset, but it is work in progress for now.

regards,
John

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LDC5072-Q1: Offset error in SIN/COS output.