Hi all, I am using the TI LDC 1001-Q1 as proximity sensor to detect metallic objects. The LDC is connected to a Microcontroller and to an external squared coil with an inductance of 220uH (inner diameter/ outer diameter = 0.86). The input capacitor is 10nF, resulting in an LC frequency of about 105 kHz. The LDC together with the microcontroller and other components, are soldered in a PCB, being only the coil external.
However, considering two identical PCBs (with LDC included), with the identical external coil and with the same firmware, I notice two different behaviours:
- One group of PCBs is working well, with a proximity data of 4500 when no metal object is on top , and Rp of about 8KOhm
- Another group of PCBs is not working well, with a proximity data of about 18000 when no metal object is on top, and a resulting Rp of 2KOhm.
In attachment you can find that the PCBs were programmed with the identical firmare (Rpmin, Rpmax, and the hardware is identical, with the same LC frequency) and the same coil is used for both of them.
For all the PCBs, I am using:
1) Capacitor of 10nF between INA and INB
2) Bypass capacitor of 56nF
3) Filter capacitor of 22pF between CFA and CFB
Please could you help me in understanding the different behaviour of two nominally identical PCBs BUT with different proximity and the resulting different Rp ? What exactly influences the proximity value (considering for both the PCB that are in the same condition with no metal around and the same coil) ?
Please let me know,
Best,
Donato.