LDC1614: spikes in the coils measurements

Francesco Buffa

Part Number: LDC1614

Hello,

we have a custom boards with the LDC1614 on board and four 4 layers pcb coils.

While acquiring data, in this case during a temperature sweep, we have some spikes in the measurements (see the picture below, the x axes represents the samples, roughly one per second). We are checking the STATUS register and there seem to be no errors rising (ERROR_CONFIG is set to show everything but the DRDY).

The coils are very close to the LDC (a couple of cm traces), the board is surrounded by an aluminum case grounded to the pcb GND. Deglitch filter is set to 3.3MHz.

What could be the reason for these spikes?Anything in particular we could check?

Thanks,

Francesco

over 4 years ago

0 Kristin Jones93 over 4 years ago

TI__Genius 17440 points

Hi Francesco,

Spikes are often caused by incorrect deglitch filter settings. Please follow the steps in this FAQ and let me know if this helps: https://e2e.ti.com/support/sensors/f/1023/t/295036#Q30

Best Regards,

0 Francesco Buffa over 4 years ago in reply to Kristin Jones93

Prodigy 100 points

Hello Kristin,

I checked the MUX_CONFIG register and it looks correct, I read 0xC20C which should be the correct value.

I forgot to mention that the frequencies in the plot above were multiplied by -1 to check the trend versus the temperature, but anyway the values don't go above 3.3MHz, which is the value for the deglitch filter that we have.

Regards,

Francesco

0 Kristin Jones93 over 4 years ago in reply to Francesco Buffa

TI__Genius 17440 points

Hello Francesco,

My apologies for the delayed reply. Since the deglitch filter is set correctly, could you also verify that the sensor oscillation amplitude is within the ideal range (1.2V-1.8V) ? If the sensor oscillation amplitude is too low, it can be easier for EMI to couple into the sensor.

Best Regards,

0 Kristin Jones93 over 4 years ago in reply to Kristin Jones93

TI__Genius 17440 points

Hello,

I haven't heard from you in a while, so I'm assuming you were able to resolve your issue. If this is not the case please feel free to reply to this thread or post a new question.

Best Regards,

0 Francesco Buffa over 4 years ago in reply to Kristin Jones93

Prodigy 100 points

Hello,

checking with the oscilloscope would be difficult, no easy way to access the coils, but as said in the original question STATUS register is not rising any amplitude error. If it's reliable I think we can exclude this situation.

Regards,

0 Kristin Jones93 over 4 years ago in reply to Francesco Buffa

TI__Genius 17440 points

Hello Francesco,

There can be some tolerance for the amplitude errors as they are not tested in production (which is why you don't see them specified in the electrical characteristics table). I do recommend checking the amplitude with an oscilloscope if you can find a way.

Since you mentioned that the coils are hard to access, are they located remotely from the LDC1614? Any time long cables or wires are introduced to the system there's a chance that EMI can couple into the system, which could cause the spikes you're seeing.

Best Regards,

0 Francesco Buffa over 4 years ago in reply to Kristin Jones93

Prodigy 100 points

Hello Kristin,

I'll try to see if I can reach the coils with an oscilloscope.

As mentioned in the original question, there are just a couple of cm PCB traces between the coils and the LDC1614.

Best regards,

0 Kristin Jones93 over 4 years ago in reply to Francesco Buffa

TI__Genius 17440 points

Hello Francesco,

If your oscillation amplitude is within the optimal range, this application note may help you eliminate EMI in your inductive sensing system.

Best Regards,

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LDC1614: spikes in the coils measurements