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LDC1312: Sensor DATA not updating randomly, no error flags, only fixed with RESET

Jeff Zhang
Prodigy 30 points
Part Number: LDC1312

We ran into a rare instance where the sensor DATA reading will not update after running for a while. We have built many of our sensors with no issues before so this is probably a hardware issue.

Bug:

The sensor will stop updating all of a sudden (while reading and writing registers still work) after anywhere from several seconds to several minutes from a power-cycle. The STATUS register is all zeros despite all error flags enabled. There aren't any timeouts and the I2C protocol is not stuck waiting for a flag or anything like that. I could only make it work again for a while if I 1. power cycle the sensor or 2. send 0x8000 to the RESET_DEV then initializing my registers again.

What are some ways to detect whether my values are frozen by just reading the DATA registers (the error fields are all reading normal)? What might be a root cause of this, and what does sending 0x8000 to the RESET_DEV?

Thanks for responding to this long post! 

Configuration:

CONFIG: 0x1601
ERROR_CONFIG: 0xF8FD (all enabled)
RESET_DEV: 0x0200
DRIVE_CURRENT_CH1: 0xF800
DRIVE_CURRENT_CH0: 0xF800
MUX_CONFIG: 0x820F
CLOCK_DIVIDERS_CH1: 0x1001
CLOCK_DIVIDERS_CH0: 0x1001
SETTLECOUNT_CH1: 0x0007
SETTLECOUNT_CH0: 0x0007
RCOUNT_CH1: 0x0200
RCOUNT_CH0: 0x0200
  • 0
    TI__Mastermind 18545 points

    Hello, 

    I have a couple clarifications questions for you regarding this issue: 

    • Is this issue occurring on multiple sensors? If so, is it happening on all sensors or only some of them? 
    • Can you look at the sensor waveform on an oscilloscope? If possible, can you share scope shots of the sensor while being able to read data and after it is stuck? 

    Thank you, 

    Justin Beigel

  • 0 in reply to Justin Beigel
    Prodigy 30 points

    Thanks for the fast response. We have many sensor built and this is the only one that has this issue. I'll update you next week when our electrical engineer comes back to take a look at it.

  • 0 in reply to Jeff Zhang
    TI__Mastermind 18545 points

    Hello, 

    Okay. When they are back, is it also possible to get the sensor design parameters and layout for the sensor with issues? 

    Thank you, 

    Justin Beigel

  • 0
    Prodigy 30 points

    Hi Justin, we're probed the sensor lines and it turns out that the sensor sinusoid will stop when it transitions from working to not working. We have two sensors hooked up. Basically one of the two sensors will stop working, and moments later the other one will too.

  • 0 in reply to Jeff Zhang
    Prodigy 30 points

    our EE is getting the scope screenshots together and he can give a fuller update, but it's pretty much what I've described.

  • 0 in reply to Jeff Zhang
    TI__Mastermind 18545 points

    Hello, 

    When the oscillation stops, are you still able to read the status register? Is there any change that happens in the status register just before or at the same time the oscillation stops? Scope shots of the waveform while it is operating would still be helpful to determine quality of the oscillation before it stops. 

    Best Regards, 

    Justin Beigel

  • 0
    Prodigy 10 points

    Hi Justin, 

    I attached images of both channel IN0 when the chip is outputting data and IN0 when data has stopped. In this case when the data stopped updating the oscillation completely stopped on channel IN1 and channel IN0 had continuous oscillation instead of the expected packets. It appears either channel somewhat randomly fails first. After a minute or two the channel with continuous oscillation will stop and there will be no signal on either channel. 

    My probes had rather long leads to probe these points, let me know if you need cleaner images and I can reprobe. 

    Thanks, Andrew

  • 0 in reply to Andrew Rauch
    TI__Mastermind 18545 points

    Hello Andrew, 

    Based on the waveforms you shared, the first step would be to decrease the IDRIVE setting to ensure each channel waveform is below 1.8V peak. For more information on this, see the Setting LDC1312/4, LDC1612/4, and LDC1101 Sensor Drive Configuration application note. 

    Let me know if the issue still persists after changing the register setting. 

    Best Regards, 

    Justin