Datasheet

0
5000
10000
15000
20000
25000
30000
12 17 22 27 32 37 42 47
Code (decimal)
Rp (K)
C001
0
2
4
6
8
10
12
14
16
18
20
0 1 2 3 4 5 6 7 8
Rp (K)
Distance (mm)
C001
LDC1000
SNOSCX2 –SEPTEMBER 2013 www.ti.com
Figure 11 below shows the variation in Rp as a function of distance for a 14mm diameter PCB coil(23 turns,4 mil
trace width, 4mil spacing between trace,1oz Cu thickness,FR4). Target used is a Stainless steel 2mm thick.
Figure 11. Typical Rp Vs Distance with 14mm PCB Coil
Measuring Parallel Resonance Impedance and Inductance with LDC1000
The LDC1000 is an Inductance-to-Digital Converter that simultaneously measures the impedance and resonant
frequency of an LC resonator. It accomplishes this task by regulating the oscillation amplitude in a closed loop
configuration to a constant level, while monitoring the energy dissipated by the resonator. By monitoring the
amount of power injected into the resonator, the LDC1000 can determine the value of Rp; it returns this as a
digital value which is inversely proportional to Rp. In addition, the LDC1000 can also measure the oscillation
frequency of the LC circuit; this frequency is used to determine the inductance of the LC circuit. The oscillation
frequency is returned as a digital value.
The LDC1000 supports a wide range of LC combinations, with oscillation frequencies ranging from 5kHz to
5MHz and Rp ranging from 798Ω to 3.93MΩ. This range of Rp can be viewed as the maximum input range of an
ADC. As illustrated in Figure 11, the range of Rp is typically a much smaller than maximum input range
supported by the LDC1000. To get better resolution in the desired sensing range, the LDC1000 offers
programmable input range through the Rp_MIN and Rp_MAX registers. Refer to Calculation of Rp Min and Rp
Max below for how to set these registers.
When the sensor’s resonance impedance Rp drops below the programed Rp_MIN, the LDC’s Rp output will clip
at its full scale output. This situation could for example happen when a target comes too close to the coil.
Figure 12. Transfer Characteristics of LDC1000 with Rp_MIN= 16.160 kΩ and Rp_MAX= 48.481 kΩ
10 Copyright © 2013, Texas Instruments Incorporated
Product Folder Links: LDC1000