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LDC3114-Q1: Manual Trigger of Scan Cycle - Issue in obtaining Interrupt

Jonathan Navor
Genius 9355 points
Part Number: LDC3114-Q1
Other Parts Discussed in Thread: LDC1314, LDC3114

Hi Guys,

Good day. I'm posting this in behalf of the customer. Could you help us. 

I am trying to migrate from LDC1314 to LDC3114 due to performance and cost reasons. With the LDC1314, I had four different coils connected to the four channels and I was able to trigger each of them separately for a specific amount of time (say 1ms). This was possible without having to go to the config mode -> on the fly. This enabled me to synchronize this measurement with my microcontroller, where I have other measurements running -> 5ms cycle.

I tried to synchronize the scan cycle to a 5ms cycle, using the CONFIG mode of the LDC. I made the LDC to go to config mode so that I can "stop" the measurement and start it again, whenever I want. This seemed to work, but then for the next measurement cycle that followed, I did not get any Interrupt at all. It means, once the LDC is back from config mode, it requires two complete measurement cycle to provide interrupt and valid data.

According to the datasheet, the new scan cycle will start within 1ms, after the LDC is brought back to normal operation.
My question -> why does the LDC takes two scan cycle to provide the interrupt, when it comes back from the config mode?

Please see attached documents below

Manual Trigger of Scan Cycle issue.zip

Thank you in advance for the support. 

Best regards,

Jonathan

  • 0
    TI__Genius 10070 points

    Hi Jonathan,

    Thank you for posting and for the thorough background information.

    I will update this thread by the end of the day tomorrow after reviewing the information and discussing with colleagues. 

    Best regards,

    Nicole

  • 0 in reply to Nicole Khoury
    TI__Genius 10070 points

    Hi Jonathan,

    At start-up the device requires two scan cycles to output data. Figure 8-5 in the datasheet shows the power on timing of the LDC3114:

    The device response to a single button press can be seen in Figure 8-13. There are two scan cycles following INTB, and the interrupt will be active until the end of that cycle. It appears that there are two cycles, but the extra cycle is when the button is released.

    Is the device being reset between measurements? If this is the case, two scan cycles will be seen before data is available, as this is equivalent to a power-on timing event. Additionally, I would recommend using Low Power Mode to minimize current.

    Best regards,

    Nicole

  • 0 in reply to Nicole Khoury
    Prodigy 130 points

    Hi Jonathan, Hi Nicole,

    Thank you so much for creating and responding to this forum post.

    The device is not being reset at any point of time (apart from the startup sequence). And I am using individual coils to measure their raw inductance values and hence, do not use the button press algorithm.

    As seen in the figure above, I read the status and OUT register to confirm the RAW data and de-assert the INTB pin, and then read the RAW data from all channels. I then place the LDC into config mode (Red box) and then release it from the config mode at a specific time interval, so that the complete operation can be synchronised with other processes. But whenever I am placing the LDC into config mode and getting it back, it always requires two complete scan cycles before I can have the raw data.

    I tried polling for the data ready flag after placing it to config mode, but it was unfruitful. Right now, I am using the auto-scan cycle to obtain new inductance values every 5ms. But the only pitfall is, I cannot control when the next cycle will start.

    Regards,

    Naveen Sankaran.

  • 0 in reply to Naveen Sankaran
    TI__Genius 10070 points

    Hi Naveen,

    I am still attempting to re-create in the lab what you are seeing when placing the device in and out of Config mode, and I am hoping to have more conclusive results by Thursday of this week.

    Thank you for your patience.

    Best regards,

    Nicole

  • 0 in reply to Nicole Khoury
    Prodigy 130 points

    Thank you, Nicole.

  • 0 in reply to Naveen Sankaran
    TI__Genius 10070 points

    Hi Naveen,

    What is the setting for LCDIV and SENCYCn? These parameters will set the number of sensor oscillation cycles used to determine the sampling window.

    Best regards,

    Nicole

  • 0 in reply to Nicole Khoury
    Prodigy 130 points

    Hi Nicole,

    The LCDIV is 0 and SENCYCn is 20. The sensor coil frequency is around 3.6 MHz and I wanted the sampling window to be less than 1ms.

    Regards,

    Naveen.

  • 0 in reply to Naveen Sankaran
    TI__Genius 10070 points

    Hi Naveen,

    Thank you for the clarification. I will update this thread by the end of the day tomorrow.

    Best regards,

    Nicole

  • 0 in reply to Nicole Khoury
    TI__Genius 10070 points

    Hi Naveen,

    I have confirmed using the LDC3114EVM that there are two data cycles seen before the interrupt pin is asserted. This happens when the device is first taken out of Config mode, as you have observed. It is possible that taking the device out of Config mode is seen as a power-on timing event and as a result two scan cycles will be seen before data is available. 

    Best regards,

    Nicole

  • 0 in reply to Nicole Khoury
    Prodigy 130 points

    Hi Nicole,

    Thank you for your confirmation tests. Is there any other way that you see, where I can manually trigger this scan cycle, with just one scan cycle instead of two (as we have observed) ?

    Currently, it seems we can have no absolute control as to when each scan cycle will start; we might have an idea of when it will happen but we cannot control it.

  • 0 in reply to Naveen Sankaran
    TI__Genius 10070 points

    Hi Naveen,

    I will reach out to our design team for more details on this device behavior and will update this thread.

    Best regards,

    Nicole

  • 0 in reply to Nicole Khoury
    Prodigy 130 points

    Thank you, Nicole. Much appreciated.

  • 0 in reply to Naveen Sankaran
    TI__Genius 10070 points

    Not a problem, thank you for your patience.

    Best regards,

    Nicole

  • 0 in reply to Nicole Khoury
    TI__Genius 10070 points

    Hi Naveen,

    The fastest scan rate possible is 160 SPS, which will give a scan cycle of 6.25 ms. Additionally, the 66 ms startup time is independent of scan rate. 

    With regards to device behavior when exiting config mode, it appears that the internal logic needs at least one cycle to complete in order to verify the values before changing the state of INTB. As such, there is no setting to change this and instead start at the first scan cycle.

    Best regards,

    Nicole

  • 0 in reply to Nicole Khoury
    Prodigy 130 points

    Hi Nicole,

    Thanks for the update. It will be great if you can include this detail on to the datasheet as well, if possible.

    Thanks again, Nicole.

    Regards,

    Naveen.

  • 0 in reply to Naveen Sankaran
    TI__Genius 10070 points

    Hi Naveen,

    Thank you, I have made sure to reach out internally regarding this datasheet clarification.

    Best regards,

    Nicole