AN11524
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© NXP Semiconductors N.V. 2015. All rights reserved.
Application note
Rev. 1 — 17 February 2015
32 of 54
NXP Semiconductors
AN11524
NXQ1TXA6 Evaluation Board
7.6 NFC antenna tuning capacitor
Due to the variation in shapes and dimensions of different NFC antennas, it is inevitable
that the NFC antenna should be tuned for a new design. Tune the resonance
frequency of the intended antenna to match close to 13.56 MHz. It can be done with the
parallel capacitor C704. Capacitor dielectric must be C0G/NP0 type. If the resonance
frequency is too low after removing parallel capacitor C704, the 1 nF value of the series
capacitors C705 and C706, can be lowered.
The internal capacitance of the NFC IC NT3H1201 (U701) is 50 pF typical (refer to
NT3H1201 data sheet).
The NFC functionality is optional and not needed for creating a wireless charging base
station with NXQ1TXA6 controller.
Fig 18. Temperature sensing circuit
aaa-016354
C201
10 nF
NTC201
R201
10 kΩ
measure temperature
optional
NTC
(1)
LP_VSUP
Fig 19. Tuning capacitor NFC antenna
aaa-015898
C704
C705
NFC
NFC coil
C706
3
2
1
6
7
5
3
LA
U701
VCC
NFC interface
VOUT
SDA
SCL
4
FD
2
VSS
1
LB
8
