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LDC1000 Sample Rate from Stand-by

Joel Brunetti
Prodigy 15 points

I'm looking at using the LDC1000 in a battery operated industrial setting in conjunction with 20 other sensors all being polled at 1500 to 2000 Hz.  

We use 60 to 120 of these sensor packages in close proximity to one another at the same time. Therefore, we require putting the sensor in Stand-by Mode to reduce interference with neighboring sensor packages and to reduce power consumption.  

I have some questions about sampling at these frequencies.

From the datasheet and some other forum posts I think the communication procedure with the LDC1000 is as follows:

  1. Configure the device to be in Stand-by Mode and enable DRDYB.
  2. When a sample is required, enable Active Mode.
  3. Wait for INTB falling edge.
    1. Read proximity and frequency data.
    2. Discard data as sensor is not yet stabilized.
  4. Repeat step 3 for a total of 3 times.
  5. Wait for INTB falling edge.
    1. Read proximity and frequency data.
    2. Record result.
  6. Enable Stand-by Mode to reduce power consumption and disable the inductor.

So, ignoring SPI transaction times, it takes a minimum of 4 samples to get a stable sample from the LDC1000 after being in Stand-by Mode.

Below is the calculated ODR for the EVM as well as one Webench Example that would suit our application:

Output Data Rate
EVM Min EVM Max Webench Examples
L (uH) 75.85
C (pF) 13.35
Fcount 3091 3411
Fext (kHz) 8000 8000
Fsensor (kHz) 165.64 150.10 158.16
Response Time  192 192 192
Output Data Rate (KSPS) 2.59 2.35 2.47

Given the maximum Fext of 8Mhz and minimum response time of 192 both the EVM coil and the Webench coil have ODR of ~2.5 KSPS. Given that it takes 4 samples after Stand-by for a stable sample this puts the effective sample rate at 0.6 KSPS.

Is there any way to improve the sample rate either by increasing the clock speed or reducing stabilization time?

We are currently using an in house method to measure the inductance but the LDC1000 shows promise in being both more accurate and repeatable.

Thank you for your help!