User's Manual

TOBY-R2 series - System Integration Manual
UBX-16010572 - R04 Design-in
Page 85 of 147
2.3.3 Module / host configuration selection
2.3.3.1 Guidelines for HOST_SELECTx circuit design
Selection of module / host configuration over HOST_SELECT0 and HOST_SELECT1 pins is not supported:
the two pins should not be driven by the host application processor or any other external device.
TOBY-R2 series modules include two pins (HOST_SELECT0 and HOST_SELECT1) for the selection of the module
/ host application processor configuration.
Do not apply voltage to HOST_SELECT0 and HOST_SELECT1 pins before the switch-on of their supply
source (V_INT), 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 before V_INT switch-on.
ESD sensitivity rating of the HOST_SELECT0 and HOST_SELECT1 pins is 1 kV (HBM as per JESD22-A114).
Higher protection level could be required if the lines are externally accessible and it can be achieved by
mounting an ESD protection (e.g. EPCOS CA05P4S14THSG varistor array) close to accessible points
If the HOST_SELECT0 and HOST_SELECT1 pins are not used, they can be left unconnected on the
application board.
2.3.3.2 Guidelines for HOST_SELECTx layout design
The pins for the selection of the module / host application processor configuration (HOST_SELECT0 and
HOST_SELECT1) are generally not critical for layout.