BlueMod+S50 Hardware User Guide
1VV0301505 Rev. 1 Page 21 of 53 2018-03-02
NFC Function
Functionality is defined project specific in the firmware used.
The NFCT peripheral supports communication signal interface type A and 106 kbps bit rate
from the NFC Forum. With appropriate software, the NFC peripheral can be used to emulate
the listening device NFC-A as specified by the NFC Forum.
Main features for the NFC peripheral:
• NFC-A listen mode operation
• 13.56 MHz input frequency
• Bit rate 106 kbps
• Wake-on-field low power field detection (SENSE) mode
• Frame assemble and disassemble for the NFC-A frames
• Programmable frame timing controller
• Integrated automatic collision resolution, CRC and parity functions
4.9.1. NFCT Antenna Recommendations
The NFCT antenna coil must be connected differential between NFCANT1 and NFCANT2
pins of BlueMod+S50.
Two external capacitors Ctune1/2 connected between the NFCANTx pins and GND should
be used to tune the resonance of the antenna circuit to 13.56 MHz.
Figure 13: BlueMod+S50 NFC Antenna Tuning
=
2
(
2 × 13,56
)
2
×
−
−
=
1
=
2
=
1
=
2
( )
=
1
=
2
= 4
4.9.2. Power Back Feeding
If the NFC antenna is exposed to a strong NFC field, power back feeding may occur. That
means, current may flow in the opposite direction on the supply due to parasitic diodes and
ESD structures.
If a battery is used that does not tolerate return current, a series diode must be placed
between the battery and the BlueMod+S50 in order to protect the battery. An ultra-low
forward voltage schottky diode should be chosen to keep the battery life reduction as small
as possible.
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