Hello there,
I would like to ask about the role of C4, C5, C6 and C7 capacitors in section 2.3 in snou137 manual.
...When operating in an electrically noisy environment or with extended distances to a remote sensor, it may be necessary to populate C4+C5 to improve the measurement ENOB. The components are left unpopulated by default, and the footprints are located on the bottom of the PCB. For additional noise suppression, R1 & R2 can be removed and a common-mode choke (e.g. SRF3216-222Y) can be placed into those two footprints.
In the rare case where EMI interference is caused by the LDC1101, it may be mitigated by populating C6+C7 with capacitors that are approximately 10% of the value of CSENSOR. The components are left
unpopulated by default, and the footprints are located on the bottom of the PCB. For some sensors, such as wire-wound inductors, it may not be easy to connect a sensor capacitor. A second capacitor footprint – CSENSOR2 - is included for such a situation. This is left unpopulated by default, with the footprint located on the bottom of the PCB...
I wanted to use 3 ft long cable to run LC part externally. Capacitor was close to coil. Coil was wire wound single layer solenoid 26 uH. I used high value of capacitor to get close to lower limit of LDC1101 (3300pF). The twisted pair of Ethernet cables were used CAT5 with shield, CAT6 without shield and coaxial cable RG-316. Neither of them really worked. It had trouble even to start to oscillation without target. I understand that higher frequency may be more difficult to control with extended distances but based on LDC_Tools-ext49 at this frequency (0.544MHz) cables can be upto 6 fl long.
Same setup with 2 inch long twisted pair cable worked fine.
Would the C4 - C7 help to stabilize the oscillation?
What is generally better for best performance? Short cables, LDC1101 as close as possible, C4-C7 unused?
I am asking to make sure whether this footprint should be addedd to layout design of future sensor.
Thank you very much,
Best Regards.
Michael
