Integration Manual

SARA-R4/N4 series - System Integration Manual
UBX-16029218 - R11 System description Page 47 of 157
1.13.9 Power saving
1.13.9.1 Guidelines to optimize power consumption
The LTE Cat M1 / NB1 technology is mainly intended for applications that only require a small amount of
data exchange per day (i.e. a few bytes in uplink and downlink per day). Depending on the application
type, the battery may be required to last for a few years. For these reasons, the whole application board
should be optimized in terms of current consumption and should carefully take into account the following
aspects:
 Enable the low power mode configuration using the AT+UPSV command (for the complete description
of the AT+UPSV command, see the SARA-R4/N4 series AT Commands Manual [2]).
 Enable the power saving mode configuration using the AT+CPSMS command (for the complete
description of the AT+CPSMS command, see the SARA-R4/N4 series AT Commands Manual [2]).
 Use the UART interface instead of the USB interface as a serial communication interface, because the
current consumption of the module is ~20 mA higher when the USB interface is enabled.
 Use an application processor with a UART interface working at the same voltage level (1.8 V) as the
module. In this way it is possible to avoid voltage translators, which helps to minimize current leakage.
 If the USB interface is implemented in the design, remove the external USB VBUS voltage from the
VUSB_DET input when serial communication is not necessary, letting the module enter the Power Saving
Mode defined in 3GPP Rel.13: the module does not enter the deep sleep power saving mode if the USB
interface is enabled.
 Minimize current leakage on the power supply line.
 Optimize the antenna matching, since a mismatched antenna leads to higher current consumption.
 Monitor V_INT level to sense when the module enters power-off mode or deep sleep power saving
mode.
 Disconnect the VCC supply source from the module when it is switched off (see 2.2.1.9).
 Disconnect the VCC supply source from the module during deep sleep power saving mode (see 2.2.1.9):
using a host application processor equipped with a RTC, the module can execute a standard PSM
procedure and store the NAS protocol context in non-volatile memory, and then rely on the host
application processor for running its RTC and triggering wake-up upon need
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1.13.9.2 Functionality
When power saving is enabled using the AT+CPSMS command, the module automatically enters the low
power deep sleep mode whenever possible, reducing current consumption (see the section 1.5.1.4 and the
SARA-R4/N4 series Data Sheet [1]).
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The use of an external RTC during deep sleep power saving mode is not supported by the “00”, “01” and “x2” product versions