LISA-C2 series and FW75-C200 - System Integration Manual
UBX-13000620 - R21
Early Production Information
System description
Page 48 of 103
The GPIO pins ESD sensitivity rating is 1 kV (Human Body Model according to JESD22-A114F). 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) on the lines connected to these pins, close to accessible points.
An application circuit for a typical GPIOs usage is described in Figure 24:
•
GPS supply enable function provided by the
GPIO2
pin
•
GPS data ready function provided by the
GPIO3
pin
Use transistors with at least an integrated resistor in the base pin or otherwise put a 10 k
Ω
resistor on the
board in series to the GPIO.
If the GPIO pins are not used, they can be left unconnected on the application board.
Any external signal connected to GPIOs must be tri-stated when the module is in power-down mode, when
the external reset is forced low and during the module power-on sequence (at least for 3 s after the start-
up event), to avoid latch-up of circuits and allow a proper boot of the module. If the external signals
connected to the module cannot be tri-stated, insert a multi channel digital switch (e.g. Texas Instruments
SN74CB3Q16244, TS5A3159, or TS5A63157) between the two-circuit connections and set to high
impedance during module power down mode, when external reset is forced low and during power-on
sequence.
LISA-C200: Pay special attention when using voltage level shifter connections. V_INT (1.8 V) is
provided to support biasing of level shifter ASICs. A problem can result with certain level shifter
interface buffers, which can back feed voltage to the V_INT line preventing the modem from
powering off and/or resetting properly. The back feed voltage typically comes from a host output
through the level shifter and out either from the level shifter VCC pin connected to V_INT or to
the modem GPIO input lines though an internal protection diode with modem. With modem
VCC = 0 V, a measured voltage can range from 0.3 to 1.0 V on the V_INT, preventing modem from
ever resetting or powering up or down properly.