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LDC2114EVM: can not work correctly with LC sensors from LDC1612 EVM and LDC1000 EVM

Part Number: LDC2114EVM
Other Parts Discussed in Thread: LDC1612, LDC2114, LDC1000EVM, LDC1612EVM

Hi, Team

My appliance customer is evaluating LDC2114 EVM for touch on metal application. We test LDC2114 EVM with LC sensors cut from LDC1612 EVM and LDC1000 EVM.

I remove the C3~C6 on LDC2114 EVM, connect LC sensor from LDC1612 EVM to IN2/COM, and connect LC sensor from LDC1612 EVM to IN1/COM.

1. Using LC sensor from LDC1612 EVM

The waveform on IN2 pin to GND should be correct. The sensor frequency is about 1.97MHz. The resonant frequency will increase if I put metal close to the snesor PCB coil.

But he data output on GUI is incorrect. I have set freqeuncy to "1MHz to 3.3MHz". No matter how I chagne the Rp setting, Gain setting, and Sensor Cycle
Count setting, it still can not fix the issue. The STATUS register changing between 0x40 to 0x44 frequently, and will be 0xC4 sometimes.

2. Using LC sensor from LDC1000 EVM

The waveform on IN1 pin to GND should be correct. The sensor frequency is about 3.52MHz. The resonant frequency will increase if I put metal close to the snesor PCB coil.

But he data output on GUI is changing between 0 and -1. I have set freqeuncy to "1MHz to 3.3MHz". No matter how I chagne the Rp setting, Gain setting, and Sensor Cycle
Count setting, it still can not fix the issue. The STATUS register changing between 0x40 to 0x44 frequently, and will be 0xC4 sometimes.

How can I make LDC2114 EVM work correctly with LC sensors form LDC1612 EVM and LDC1000 EVM?

Thanks
Kevin Zhang

  • Hello,
    It sounds like the settings may not be set properly for all of the channels. When the Status register reads 44, this means that there is a LC Sensor Watchdog Error (LC_WD). Typically this means that either that the Rp value of the sensor is too low to oscillate or that the sensor is disconnected on one of the channels. When you remove C3 - C6 but leave IN0/COM and IN3/COM floating and do not disable them in the register settings then you will get a LC_WD error in the status register.
    The C4 status reading means that the OUT_STATUS bit is toggling, which essentially indicates that one of the channels is crossing the threshold and the corresponding OUT pin is toggling. From the screenshot it appears that channel 2 may have the gain setting too set too high. Note that the OUT_STATUS is the logic OR of the output bits from the OUT register (0x01).
    To correctly configure the part you should only enable channels that have sensors attached and the set the proper settings for your sensor Rp and frequency. To assist with setting the registers properly you can use the LDC2114_Config_tool which is located in the LDC tools spreadsheet: www.ti.com/.../slyc137
    Also note that in general we recommend to populate the sensor capacitor near the device (caps C3-C6). It will work if you populate the capacitors near the sensor as the LDC1612EVM or LDC1000EVM has, but you will get optimal performance if you put the capacitors on the EVM closer to the device.
    Let me know if you're able to resolve the issue by following these steps.
    Thanks!
    Luke