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CD40106B: Behavior of the trigger

Sebastian Meneses
Prodigy 10 points
Part Number: CD40106B
Other Parts Discussed in Thread: TLV1811

Tool/software:

Hello, I am Sebastián Meneses, the reason for the inquiry is that we are using this trigger (part number CD40106BPWR) for a simple capacitive detection, but I have found differences in behavior in various integrated circuits (of the same part number) being the pcb the same. What we have noticed is that the mark is not entirely the same. I am attaching images

      

As you can see both images are marked with CM0106B on the first line.

the other 2 lines whare(ie 15k G4, ACY0) are for?

In some cases, we have found huge differences in capacitive detection due to differences in integrated circuits.

Could this be due to variability in the trigger's input capacitance from datasheet 5 pF typ, 7pF Max? 

Thank you in advance,

Kind regards,

Sebastian Meneses

  • 0
    TI__Mastermind 25670 points

    Sebastian,

    Could you describe the sort of differences you are seeing? Without an example of discrepancies in the input/output behavior, as well as the behavior you are expecting, it is hard to provide an assessment.

    Best,

    Malcolm

  • 0
    Guru 316510 points

    The input capacitance might have small variations, but it is more likely that the input switching threshold voltages vary.

    Please show the schematic. If you want precise analog characteristics, you probably have to use a comparator instead.

  • 0 in reply to Malcolm Lyn
    Prodigy 10 points

    I attach the schematic:



    We generate a square signal of 50 kHz, from 0 to 12V. When the human tocuhes the electrode we perform a Low-pass filfter with the 220 Kohm resistance and our body capacitance(~10 to 200 pF), the detection is done by the trigger threshold.

    The electrode is an aluminum handlebar grip, and we want it to detect when we touch this grip with the palm of our hand.

    The sensivity of the detection varies depending on the mounted trigger:

    In some cases 1 kind of trigger "detects" you from 10mm of distance, others doesn't "detect" you even when touching it with the whole hand. 

    The batch of the triggers is correlative with the differences, triggers of same batch works similar at least.

  • +1 in reply to Sebastian Meneses
    Guru 316510 points

    This circuit assumes that the LPF reduces the square wave's amplitude so much that the voltage no longer crosses the trigger threshold voltages. The CD40106B datasheet allows a wide range of threshold voltages, and it is likely that different die revisions have different thresholds.

    Replace the inverter with an inverting comparator circuit (e.g. TLV1811) with exactly the desired amount of hysteresis.

  • 0 in reply to Clemens Ladisch
    Prodigy 10 points

    Hi Clemens, 

    I got it.

    Thank you for your quick answer!