SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R26
Design-in
Page 117 of 217
2.3.3
32 kHz signal (EXT32K and 32K_OUT)
The
EXT32K
and
32K_OUT
pins are not available on SARA-G340, SARA-G350 and SARA-U2 modules.
2.3.3.1
Guidelines for EXT32K and 32K_OUT circuit design
Figure 54 describes how the
32K_OUT
output can be connected to the
EXT32K
input, providing the 32 kHz
signal which constitutes the Real Time Clock (RTC) reference clock, so that SARA-G300 / SARA-G310 modules
can enter the low power idle mode, reaching low current consumption figures (refer to section 1.5.1.4 and to
the
SARA-G3 series Data Sheet
[1]), and can provide the RTC functions when the module is switched on.
24
32K_OUT
SARA-G300
SARA-G310
31
EXT32K
Figure 54: EXT32K application circuit using the 32 kHz signal provided by the 32K_OUT output
Figure 55 and Table 35 describe how an external oscillator can be connected to the
EXT32K
input, providing the
32 kHz signal which constitutes the RTC reference clock, so that SARA-G300 / SARA-G310 modules can enter
the very low power idle mode, reaching very low current consumption figures (see section 1.5.1.4 and the
SARA-G3 series Data Sheet
[1]), and can provide RTC functions (available with
V_BCKP
voltage in the operating
range).
2
V_BCKP
GND
SARA-G300
SARA-G310
31
EXT32K
32 kHz Oscillator
GND
CLKOUT
OE
VCC
C1
U1
Figure 55: EXT32K application circuit using an external 32 kHz oscillator
Reference
Description
Remarks
C1
100 nF Capacitor Ceramic X7R 0402 10% 16 V
GRM155R61A104KA01 - Murata
U1
Low Power Clock Oscillator 32.768 kHz
OV-7604-C7 - Micro Crystal or SG-3040LC - EPSON TOYOCOM
Table 35: Example of components for the EXT32K application circuit
The two different solutions described in Figure 54 and Figure 55 are alternatives and mutually exclusive: only one
of the two proposed solutions can be implemented according to the required current consumption figures for
the idle mode (for the detailed characteristics see the
SARA-G3 series Data Sheet
Alternatively, a proper 32 kHz signal can be provided to the
EXT32K
input by the used application processor.
The ESD sensitivity rating of the
EXT32K
input pin and the
32K_OUT
output pin is 1 kV (Human Body
Model according to JESD22-A114). A higher protection level can be required if the line is externally
accessible on the application board. A higher protection level can be achieved by mounting an ESD
protection (e.g. EPCOS CA05P4S14THSG varistor array) close to accessible points.
If the customer application does not require the low power idle mode and the RTC functions, the
EXT32K
input pin and the
32K_OUT
output pin can be left not connected.
