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TOBY-R2 series - System integration manual
UBX-16010572 - R10
Design-in
Page 84 of 151
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.