User's Manual

SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R18 Advance Information Design-in
Page 134 of 206
Any external signal connected to the auxiliary UART interface must be tri-stated or set low when the
module is in power-down mode and during the module power-on sequence (at least until the activation
of the V_INT output), to avoid latch-up of circuits and allow a proper boot of the module. If the external
signals connected to the cellular module cannot be tri-stated or set low, insert a multi channel digital
switch (e.g. TI SN74CB3Q16244, TS5A3159, or TS5A63157) between the two-circuit connections and set
to high impedance during module power down mode and during the module power-on sequence.
ESD sensitivity rating of auxiliary UART pins is 1 kV (Human Body Model according to JESD22-A114).
Higher protection level could be required if the lines are externally accessible on the application board.
Higher protection level can be achieved by mounting an ESD protection (e.g. EPCOS CA05P4S14THSG
varistor array) close to accessible points.
2.6.2.2 Guidelines for UART AUX layout design
The auxiliary UART serial interface is not critical for the layout design since it is not used during normal operation
of SARA-G3 modules. Ensure accessibility to the TXD_AUX and RXD_AUX pins providing test points on the
application board.