Product Specs

Table Of Contents
42 NFCT Near field communication tag
Page
424
Cp1
Ctune1
Cint1
NFC1
ANTENNA
Lant
Rin
NFC2
Cp2
Ctune2
Cint2
42.8 Antenna interface
In ACTIVATED state, an amplitude regulator will adjust the voltage swing on the antenna pins to a value that
is within the V
swing
limit.
Refer to NFCT Electrical Specification on page 436.
42.9 NFCT antenna recommendations
The NFCT antenna coil must be connected differential between NFC1 and NFC2 pins of the device.
Two external capacitors should be used to tune the resonance of the antenna circuit to 13.56 MHz.
Figure 122: NFCT antenna recommendations
The required tuning capacitor value is given by the below equations:
An antenna inductance of L
ant
= 2 µH will give tuning capacitors in the range of 130 pF on each pin. For good
performance, match the total capacitance on NFC1 and NFC2.
42.10 Battery protection
If the antenna is exposed to a strong NFC field, current may flow in the opposite direction on the supply due
to parasitic diodes and ESD structures.
If the battery used does not tolerate return current, a series diode must be placed between the battery and
the device in order to protect the battery.