Integration Manual

SARA-R4/N4 series - System Integration Manual
UBX-16029218 - R13 Design-in Page 40 of 119
charger / regulator with integrated power path management function can be selected to supply the module while
simultaneously and independently charging the battery. See sections 2.2.1.6 and 2.2.1.7 for specific design-in.
An appropriate primary (not rechargeable) battery can be selected taking into account the maximum current specified in
the SARA-R4/N4 series Data Sheet [1] during connected mode, considering that primary cells might have weak power
capability. See section 2.2.1.5 for specific design-in.
The usage of more than one DC supply at the same time should be carefully evaluated: depending on the supply source
characteristics, different DC supply systems can result as mutually exclusive.
The selected regulator or battery must be able to support with adequate margin the highest averaged current
consumption value specified in the SARA-R4/N4 series Data Sheet [1].
The following sections highlight some design aspects for each of the supplies listed above providing application circuit
design-in compliant with the module VCC requirements summarized in Table 6.
2.2.1.2 Guidelines for VCC supply circuit design using a switching regulator
The use of a switching regulator is suggested when the difference from the available supply rail source to the VCC value
is high, since switching regulators provide good efficiency transforming a 12 V or greater voltage supply to the typical 3.8
V value of the VCC supply.
The characteristics of the switching regulator connected to VCC pins should meet the following prerequisites to comply
with the module VCC requirements summarized in Table 6:
• Power capability: the switching regulator with its output circuit must be capable of providing a voltage value to the
VCC pins within the specified operating range and must be capable of delivering to VCC pins the maximum current
consumption occurring during transmissions at the maximum power, as specified in the SARA-R4/N4 series Data
Sheet [1].
• Low output ripple: the switching regulator together with its output circuit must be capable of providing a clean (low
noise) VCC voltage profile.
• High switching frequency: for best performance and for smaller applications it is recommended to select a switching
frequency ≥ 600 kHz (since L-C output filter is typically smaller for high switching frequency). The use of a switching
regulator with a variable switching frequency or with a switching frequency lower than 600 kHz must be carefully
evaluated since this can produce noise in the VCC profile and therefore negatively impact modulation spectrum
performance.
• PWM mode operation: it is preferable to select regulators with Pulse Width Modulation (PWM) mode. While in
connected mode, the Pulse Frequency Modulation (PFM) mode and PFM/PWM modes transitions must be avoided
to reduce noise on VCC voltage profile. Switching regulators can be used that are able to switch between low ripple
PWM mode and high ripple PFM mode, provided that the mode transition occurs when the module changes status
from the active mode to connected mode. It is permissible to use a regulator that switches from the PWM mode to
the burst or PFM mode at an appropriate current threshold.