Chris' comment on core saturation might be it. However, if your inductor is
operating as a common-mode inductor, and has no DC flux, then core
saturation will not be an issue. I did encounter a situation in which two
solenoid inductors were placed quite close together and there was a
substantial change if the magnetic fields were opposing of aiding - the
direction they were inserted into the PCB mattered. Enough of anecdotal
stories and on to the specific component.
Let's examine the Coilcraft 1812CS-102XJLC inductor that you are using. The
SRF is 310 MHz and the DC current rating is 480 mA. Coilcraft supplies
S-parameters and a SPICE model for this part. This part looks very well
behaved at 13.56 MHz. No parameters are changing much.
I wonder if your EMI filter is tuned to resonance near 13.56 MHz? This would
make the circuit more sensitive to variations in the inductor parameters.
How much is the variation in conducted EM energy between a good and a bad
inductor?
Dave Cuthbert
Linear Technology
From: [email protected] [mailto:[email protected]] On Behalf Of
[email protected]
Sent: Friday, October 06, 2006 6:02 AM
To: [email protected]; [email protected]
Subject: Inductor mystery
Dear Experts,
We use the inductor part "1812CS-102XJLC" of Coilcraft in our RFID
product as EMI filter. Continuously we face one issue, about 20 to 30 %
products are functionally failing due to this inductor. While we change the
inductor alone the product passes the functional tests. Hence we studied
the characteristics of the inductor.
Measurements carried out using the Agilent Impedance analyser 4294A
shows the failing inductors and passing inductors are identical with
respect to the below listed parameters for the entire measuring range of 40
Hz to 110 MHz. Our frequency of operation is 13.56 MHz and both the failing
inductors and passing inductors are identical in this particular frequency
also with respect to the below parameters.
Is there anything else than the below listed parameters critical for
an inductor? Has any one of you come across such an issue in your devices?
I request your help.
a. Ra.c
b. Conductance - 'G'
c. Reactance - 'X'
d. Susceptance - 'B'
e. Impedance - 'Z'
f. Phase angle of the impedance
g. Value of R, L & C measured using the equivalent circuit method of
measurement.
Sincerely
K.Balasubramanian
Project Leader - Hardware.
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