Integration Manual

SARA-R4/N4 series - System Integration Manual
UBX-16029218 - R13 Design-in Page 39 of 119
2.2 Supply interfaces
2.2.1 Module supply (VCC)
2.2.1.1 General guidelines for VCC supply circuit selection and design
All the available VCC pins have to be connected to the external supply minimizing the power loss due to series resistance.
GND pins are internally connected. Application design shall connect all the available pads to solid ground on the
application board, since a good (low impedance) connection to external ground can minimize power loss and improve RF
and thermal performance.
SARA-R4/N4 series modules must be sourced through the VCC pins with a suitable DC power supply that should meet the
following prerequisites to comply with the modules’ VCC requirements summarized in Table 6.
The appropriate DC power supply can be selected according to the application requirements (see Figure 15) between the
different possible supply sources types, which most common ones are the following:
• Switching regulator
• Low Drop-Out (LDO) linear regulator
• Rechargeable Lithium-ion (Li-Ion) or Lithium-ion polymer (Li-Pol) battery
• Primary (disposable) battery
M ain Supply
Available?
Bat t ery
Li-Ion 3.7 V
Linear LDO
Regulat or
M ain Supply
Volt age > 5V?
Swit ching St ep-Down
Regulat or
No, port able device
No, less t han 5 V
Yes, great er t han 5 V
Yes, always available
Figure 15: VCC supply concept selection
The switching step-down regulator is the typical choice when primary supply source has a nominal voltage much higher
(e.g. greater than 5 V) than the operating supply voltage of SARA-R4/N4 series. The use of switching step-down provides
the best power efficiency for the overall application and minimizes current drawn from the main supply source. See
section 2.2.1.2 for design-in.
The use of an LDO linear regulator becomes convenient for a primary supply with a relatively low voltage (e.g. less or
equal than 5 V). In this case, the typical 90% efficiency of the switching regulator diminishes the benefit of voltage step-
down and no true advantage is gained in input current savings. On the opposite side, linear regulators are not
recommended for high voltage step-down as they dissipate a considerable amount of energy in thermal power. See
section 2.2.1.3 for design-in.
If SARA-R4/N4 series modules are deployed in a mobile unit where no permanent primary supply source is available, then
a battery will be required to provide VCC. A standard 3-cell Li-Ion or Li-Pol battery pack directly connected to VCC is the
usual choice for battery-powered devices. During charging, batteries with Ni-MH chemistry typically reach a maximum
voltage that is above the maximum rating for VCC, and should therefore be avoided. See sections 2.2.1.4, 2.2.1.5, 2.2.1.6
and 2.2.1.7 for specific design-in.
Keep in mind that the use of rechargeable batteries requires the implementation of a suitable charger circuit, which is
not included in the modules. The charger circuit needs to be designed to prevent over-voltage on VCC pins, and it should
be selected according to the application requirements. A DC/DC switching charger is the typical choice when the charging
source has a high nominal voltage (e.g. ~12 V), whereas a linear charger is the typical choice when the charging source
has a relatively low nominal voltage (~5 V). If both a permanent primary supply / charging source (e.g. ~12 V) and a
rechargeable back-up battery (e.g. 3.7 V Li-Pol) are available at the same time as possible supply source, then a suitable