LDC1000-Q1_16 Datasheet, PDF (26/40 Pages) Texas Instruments – Inductance to Digital Converter

LDC1000-Q1
SLOS886B – SEPTEMBER 2014 – REVISED OCTOBER 2014
8 Application and Implementation
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NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
8.1.1 Calculation of Rp_Min and Rp_Max
Different sensing applications may have a different ranges of the resonance impedance R_P to measure. The
LDC1000-Q1 measurement range of R_P is controlled by setting two registers: Rp_MIN and Rp_MAX. For a given
application, R_P must never be outside the range set by these register values, otherwise the measured value will
be clipped. For optimal sensor resolution, the range of Rp_MIN to Rp_MAX should not be unnecessarily large.
The following procedure is recommended to determine the Rp_MIN and Rp_MAX register values.
8.1.1.1 Rp_MAX
Rp_MAX sets the upper limit of the LDC1000-Q1 resonant impedance input range.
• Configure the sensor such that the eddy-current losses are minimized. As an example, for a proximity sensing
application, set the distance between the sensor and the target to the maximum sensing distance.
• Measure the resonant impedance R_P using an impedance analyzer.
• Multiply R_P by 2 and use the next higher value from the register settings listed in Table 3.
For example, if R_P is measured at 18 kΩ, 18000 × 2 = 36000. Referring to Table 3, 38.785 kΩ is the smallest
value larger than 36 kΩ; therefore Rp_MAX should be set to 0x11.
Setting Rp_MAX to a value not listed in Table 3 can result in indeterminate behavior.
8.1.1.2 Rp_MIN
Rp_MIN sets the lower limit of the LDC1000-Q1 resonant impedance input range.
• Configure the sensor such that the eddy current losses are maximized. As an example, for a proximity
sensing application, set the distance between the sensor and the metal target to the minimum sensing
distance.
• Measure the resonant impedance R_P using an impedance analyzer.
• Divide the R_P value by 2 and then select the next lower R_P value from the register settings listed in Table 4.
For example, if R_P at 1 mm is measured to be 5 kΩ, 5000 / 2 = 2500. Referring to Table 4, 2.394 kΩ is the
smallest value smaller than 2.5 kΩ which corresponds to an Rp_MIN value of 0x3B.
Setting Rp_MIN to a value not listed on Table 4 can result in indeterminate behavior. In addition, Rp_MIN powers
on with a default value of 0x14 which must be set to a value from Table 4 prior to powering on the LDC.
8.1.2 Output Data Rate
The output data rate of the LDC1000-Q1 device depends on the sensor frequency, f_sensor and the Response
Time[2-0] field in the LDC configuration register (address: 0x04).
Output data rate = f_sensor / (Response Time[2-0] / 3) in SPS (samples per second)
(14)
8.1.2.1 Example
If the following values are selected, f_sensor= 5 Mhz and Response Time[2-0] = 192, then:
Output data rate = 5 MHz / (192 / 3) = 78.125 KSPS
(15)
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