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LDC1001-Q1: LDC1001-Q1

Donato Falcone
Prodigy 20 points
Part Number: LDC1001-Q1
Other Parts Discussed in Thread: LDC1001

Tool/software:

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.

In our application the proximity data is about 4500 when no metal object is on top , and Rp of about 8KOhm. When a metallic object is on top at about 10cm, the Rp drops at around 7kOhm. The usual working register LDC status is 48.

However, we noticed 2 anomalies in production on some of our sensors:
1) Some sensors at some point without any apparent reason transmit a status of 0, with Rpmin and Rpmax registers at 0 as well, and the Rp goes at 60352, and then they go in a condition with Rp=Rpmax. Basically our application was working fine since 2 weeks, with status 48, Rp around 8k, and all of a sudden we got this status 0 and Rp=60352, and from that instant on it was always in Rpmax with sense status of 240, so not working anymore.

2) At some point, after a couple of weeks of good behaviour, without any changes in the external condition, the Rp quickly starts to decrease in about few hours, from nominal 8k (in case no metallic object) down to 2k (in case of no metallic object), and therefore our thresholds and system do not work anymore, and the sensor show a permanent change of regime.

Please could you help us in fixing these issues in production?

Please let me know,
Thank you,

Best regards,

Donato.

  • 0
    TI__Mastermind 37605 points

    Donato,

    We are sorry to hear you are having problems with the design.
    A few questions:

    1. During the "bad" behavior, does a power-down/power-up sequence of the LDC fix the problem?
    2. Do you see this in a single unit or multiple units?
    3. Are there any changes to VCC before/during/after the event?
    4. Are there any changes to sensor signal before/during/after the event?

    Regards,
    John

  • 0 in reply to John Miller - Sensing
    Prodigy 20 points

    Dear John,

    Thanks for your help. 

    1. During the "bad" behavior, does a power-down/power-up sequence of the LDC fix the problem? We can not test this since our devices are installed in several cities and we can not remotely plug/unplug the power, so the battery.
    2. Do you see this in a single unit or multiple units? After about 2 months we see it on 10-15% of our installed devices. The "bad behavior" comes at some point, after for instance a month of regular behavior.
    3. Are there any changes to VCC before/during/after the event? If you refer to the reference voltage of 5V, I don't think so, we use a battery of 7.2V , with in parallel a capacitor (to provide stronger pulses during the transmissions) and there is a 5V 100mA LDO to provide the required 5V to the LDC1001.
    4. Are there any changes to sensor signal before/during/after the event? What we see is a regular behavior with Rp around 8kOhm, Status 48, Rpmin 60 and Rpmax 18, for months and also on all the other devices in production. Then for few devices, at some point (different for each failed devices) the Rp goes to 60352 Ohm, and the interesting things is that all the status registers of the LDC go to 0, with Status 0, Rpmin 0 and Rpmax 0.

    Do you have any clue on the fundamental reason behind this ? Our LDC are within a PCB, controlled by a micro, and exposed to ambient condition (street condition, with the temperature between 0 and 70C). However, they are included in a protective case to prevent humidity/water to enter, and also to give stability.

    We use a battery based on 2 series of ER14505, with 7.2V and 27Ah configuration, with super capacitor SPC1520A.

    Please let us know if you have any idea on which could be the reasons behind these failures,

    Thanks a lot for your effort and your help,

    Best,

    Donato.

  • 0 in reply to Donato Falcone
    TI__Mastermind 37605 points

    Donato,

    is there any other performance or fault monitoring that goes on in your system?
    Does the "bad" behavior ever correct itself?

    Regards,
    John