Telit Wireless Solutions BlueMod+S50/AI, Руководство пользователя по оборудованию

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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 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.
NFCANT1
S50
A-3
NFCANT2
A-4
C
tune1
C
tune2
C
p1
C
p2
C
int2
C
int1
NFC-Antenna
Figure 13: S50 NFC Antenna Tuning
𝐶𝐶
𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡
=
2
(2
𝜋𝜋 × 13,56 𝑀𝑀𝑀𝑀𝑀𝑀
) 2
× 𝐿𝐿
𝑎𝑎𝑡𝑡𝑡𝑡
− 𝐶𝐶
𝑝𝑝
− 𝐶𝐶
𝑖𝑖𝑡𝑡𝑡𝑡
𝐶𝐶
𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡
= 𝐶𝐶
𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡1
= 𝐶𝐶
𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡2
𝐶𝐶
𝑝𝑝
= 𝐶𝐶
𝑝𝑝1
= 𝐶𝐶
𝑝𝑝2
( 𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎 𝑎𝑎𝑡𝑡𝑎𝑎𝑡𝑡𝑡𝑡 𝑡𝑡𝑎𝑎𝑐𝑐𝑎𝑎𝑡𝑡𝑐𝑐𝑎𝑎𝑎𝑎𝑎𝑎𝑡𝑡𝑎𝑎 )
𝐶𝐶
𝑖𝑖𝑡𝑡𝑡𝑡
= 𝐶𝐶
𝑖𝑖𝑡𝑡𝑡𝑡1
= 𝐶𝐶
𝑖𝑖𝑡𝑡𝑡𝑡2
= 4 𝑐𝑐𝑝𝑝
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 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.