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FDC2214: FDC2214 inductor and external oscillator specifications

Don Foong
Expert 4100 points
Part Number: FDC2214

Hi Team,

One of our customer has evaluated and like to use our FDC2214 for the liquid-level detect solution. They need some cost down to meet target solution cost hence looking at alternate source for the inductor and the oscillator.

Kindly advise what are the key specifications need to consider selecting the inductor and the oscillator for FDC2214 circuit. With reference to the device used in the EVM such as CMH322522-180KL and CTS's 625L3C040M.

 

For the 18uH inductor, can we use 25mA for Irms-max since FDC2214 output drive is in the range of 1.5mA to 6mA (max) ?

DS stated inductor SRF must > 125% of sensor LC frequency.

What is the low limit for the Q-factor ?

What is the maximum inductor DCR that FDC2214 can drive ? 

 

For the 40MHz oscillator, what are the key specification that must be met ?

Frequency stability +/-50ppm ? Aging < +/-5ppm/yr.

can we use higher supply current >15mA device ?

 

Can you provide some calculation example relating the +/10% tolerance of the inductor to FDC2214's ADC output resolution accuracy ? Similarly the oscillator's frequency stability to FDC2214 output ENOB.

 

Look forward to your feedback, thanks in advance.

  • 0
    TI__Expert 8050 points
    Hi Don,

    For the external oscillator, 50 ppm is usually good enough to provide robust performance. The supply current should not be an issue.

    It is recommended to have a Q of at least 10 at the frequency of oscillation, although it is less critical for capacitive sensing applications. As long as the LC resonator can have stable oscillation, it should be fine. 25 mA rms max should be sufficient.

    The noise performance of surface mount inductors is very tricky. From our experience, there is not a good way to calculate it, which depends on the materials and manufacturing process. The best way to compare inductors' noise performances is to test them with the EVM and monitor the output data.

    Regards,
    Yibo
  • 0 in reply to Yibo Yu
    TI__Expert 4100 points
    Hi Yibo,

    Thanks for the support.