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LDC2112: LDC2112 raw data change with temperature at different FPC vendor

Poki Huang
Expert 1060 points
Part Number: LDC2112

Hi 

We met a problem that when we put our DUT from ambient into freezer (~ 0 degree), some DUT LDC2112 raw data will change

And we find it's because different FPC vendor (our LC coil pattern is on FPC)

The FPC vendor CMI it's LDC2112 raw data won't change, but FPC vendor Career & Unimicron will change (I attached CMI & Career's data at below)

At beginning we thought it related with thermal expansion coefficient, but when we get data from FPC vendor 

FPC vendor CMI's is larger than Career & Unimicron, so seems it not root cause

Below is three vendor's stack up(LC coil pattern is at L2/L3) 

So could you help check if anything wrong with Career & Unimicron's stackup?

Or if any material's parameter that we need to check?

Or how do we analyze this issue?

Thank you~~

Poki

LDC2112 raw data

Three FPC vendor's stack up

  

  • +1
    TI__Mastermind 33190 points

    Poki,

    Thank you for your inquiry and your interest in TI products.
    Unfortunately we are not experts in coil design, so the information we provide in our app notes is the limit of what we can offer.

    You may have checked already, but one thing to confirm is the values and TC of the capacitors connected to the coils. 
    The inductive coil and the capacitors form a resonant circuit, so the values and TC of the capacitors can be critical.

    Regards,
    John

  • 0 in reply to John Miller - Sensing
    TI__Guru* 90906 points

    I have had this sort of thing happen before, with antennas tuned at one temp and then exposed to a drastic temp change (Chicago in springtime in an outdoor application....) - check the change in inductance (with LCR or Network Analyzer) of the coils over temp - the flex material may be contracting when cold, which will change your inductance (at that frequency) and interwinding capacitance, thus changing your resonance. (as John stated) - in my case the solution was to ensure the separation material (in that case it was the actual insulation on wires) was rated for beyond the temp swings known to happen.