Battery Protection; Debug Interface - u-blox NINA-B4 Series System Integration Manual

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 L
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.
The NINA-B4 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. To comply with European regulatory demands, the NFC
antenna must be placed in such a way that the space between the NINA-B4 module and the remote
NFC transmitter is always within 3 meters during transmission.
Figure 9: NFC antenna design
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2.4.1

Battery protection

If the antenna is exposed to a strong NFC field, parasitic diodes and unintended ESD structures can
cause the current to flow in the opposite direction of the supply.
If the battery used does not tolerate a return current, protect the battery with a series diode placed
between the battery and the device.

2.5 Debug interface

NINA-B40x modules support Serial Wire debug (SWD) and Serial Wire Viewer, but not JTAG debug.
When designing your application with the NINA-B40x, the SWD interface (pins SWDCLK and SWDIO)
to the module should ideally be made available in the application design.
To allow the module to be flashed using the UART or the SWD interface, the module is preloaded with
boot loader software that is without security. A debug connector to the module is also useful during
the software development.
For security reasons, the debug interface should also be disabled to prevent the upload or download
insecure software – or software that has not been validated.
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