NINA-B1 series - System Integration Manual
UBX-15026175 - R09
Design-in
Page 34 of 49
3.4.2
Serial peripheral interface (SPI)
The layout of the SPI bus should be done so that noise injection and cross talk are avoided.
3.4.3
I
2
C interface
The layout of the I
2
C bus should be done so that noise injection and cross talk are avoided.
3.5
NFC interface
Ensure that the NFC pins are configured correctly. Connecting an NFC antenna to the pins
configured as GPIO will damage the module.
The NFC antenna coil must be connected differentially 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.
The required tuning capacitor value is given by the below equations: An antenna inductance of Lant = 2
μ
H will
give tuning capacitors in the range of 130 pF on each pin. For good performance, match the total capacitance
on NFC1 and NFC2.
The NINA-B1 modules have been tested with a 3x3 cm PCB trace antenna, so it is recommended to keep an
antenna design close to these measurements. You can still use a smaller or larger antenna as long as it is tuned
to resonate at 13.56 MHz. In order to comply with European regulatory demands, the NFC antenna must be
placed in such a way that the space between the NINA-B1 module and the remote NFC transmitter is always
within 3 meters during transmission.
Figure 13: NFC antenna design
𝐶𝐶
𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡
′
=
1
(2
𝜋𝜋
× 13.56
𝑀𝑀𝑀𝑀𝑀𝑀
)
2
𝐿𝐿
𝑎𝑎𝑡𝑡𝑡𝑡
𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤
𝐶𝐶
𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡
′
=
1
2 ×
�𝐶𝐶
𝑝𝑝
+
𝐶𝐶
𝑖𝑖𝑡𝑡𝑡𝑡
+
𝐶𝐶
𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡
�
𝐶𝐶
𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡
=
2
(2
𝜋𝜋
× 13.56
𝑀𝑀𝑀𝑀𝑀𝑀
)
2
𝐿𝐿
𝑎𝑎𝑡𝑡𝑡𝑡
− 𝐶𝐶
𝑝𝑝
− 𝐶𝐶
𝑖𝑖𝑡𝑡𝑡𝑡
3.5.1
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.
