SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R26
System description
Page 36 of 217
1.6.1.2
Switch-on sequence from not-powered mode
Figure 21 shows the module’s power-on sequence from the not-powered mode, describing the following
phases:
The external supply is applied to the
VCC
module supply inputs, representing the start-up event.
The status of the
PWR_ON
input pin while applying the
VCC
module supply is not relevant: during this
phase the
PWR_ON
pin can be set high or low by the external circuit, but in Figure 21 it is assumed that the
PWR_ON
line rises suddenly to the high logic level due to external pull-up connected to
V_BCKP
or
VCC
.
The
V_BCKP
RTC supply output is suddenly enabled by the module as
VCC
reaches a valid voltage value.
The
RESET_N
line of SARA-U2 series rises suddenly to high logic level due to internal pull-up to
V_BCKP
.
All the generic digital pins of the modules are tri-stated until the switch-on of their supply source (
V_INT
):
any external signal connected to the generic digital pins must be tri-stated or set low at least until the
activation of the
V_INT
supply output to avoid latch-up of circuits and allow a proper boot of the module.
The
V_INT
generic digital interfaces supply output is enabled by the integrated power management unit.
The
RESET_N
line of SARA-G3 series rises suddenly to high logic level due to internal pull-up to
V_INT
.
The internal reset signal is held low by the integrated power management unit: the baseband processor core
and all the digital pins of the modules are held in reset state.
When the internal reset signal is released by the integrated power management unit, any digital pin is set in
a proper sequence from the reset state to the default operational state. The duration of this pin’s
configuration phase differs between generic digital interfaces and the USB interface, due to specific
host / device enumeration timings (see section 1.9.3):
o
Generic digital interfaces pin configuration time: 3 seconds typical on SARA-G3 and SARA-U2 series
modules, except for on SARA-U201 modules, which have 4 seconds typical
o
USB interface configuration time: 5 seconds typical on SARA-G3 and SARA-U2 series modules, except
for on SARA-U201 modules, which have 6 seconds typical
The module is fully ready to operate after all the interfaces are configured.
VCC
V_BCKP
PWR_ON
SARA-U2 RESET_N
V_INT
SARA-G3 RESET_N
Internal Reset
System State
Digital Pins State
Internal Reset
→
Operational Operational
Tristate / Floating
OFF
ON
Internal Reset
0 ms
~35 ms
~3 s
Start of interface
configuration
Module interfaces
are configured
Start-up
event
Figure 21: SARA-G3 and SARA-U2 series power-on sequence from not-powered mode
