Integration Manual

TOBY-L2 and MPCI-L2 series - System Integration Manual
UBX-13004618 - R26 Design-in
Page 71 of 162
2.2 Supply interfaces
2.2.1 Module supply (VCC or 3.3Vaux)
2.2.1.1 General guidelines for VCC or 3.3Vaux supply circuit selection and design
VCC or 3.3Vaux pins are internally connected. Application design shall connect all the available pads to the
external supply to minimize 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.
TOBY-L2 and MPCI-L2 series modules must be sourced through the VCC or the 3.3Vaux pins with a proper DC
power supply that should meet the following prerequisites to comply with the modules’ VCC or 3.3Vaux
requirements summarized in Table 7.
The proper DC power supply can be selected according to the application requirements (see Figure 32) 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, for TOBY-L2 series only
 Primary (disposable) battery, for TOBY-L2 series only
Main Supply
Available?
Battery
Li-Ion 3.7 V
Linear LDO
Regulator
Main Supply
Voltage > 5V?
Switching Step-Down
Regulator
No, portable device
No, less than 5 V
Yes, greater than 5 V
Yes, always available
Figure 32: VCC supply concept selection
The switching step-down regulator is the typical choice when the available primary supply source has a nominal
voltage much higher (e.g. greater than 5 V) than the operating supply voltage of TOBY-L2 and MPCI-L2 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 2.2.1.2, 2.2.1.6, 2.2.1.9, 2.2.1.10 for specific 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 2.2.1.3, 2.2.1.6, 2.2.1.9, 2.2.1.10 for specific design-in.
If TOBY-L2 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 2.2.1.4,
2.2.1.6, 2.2.1.9, 2.2.1.10 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 has to be designed to prevent over-voltage on VCC pins of the
module, and it should be selected according to the application requirements: a DC/DC switching charger is the
typical choice when the charging source has an high nominal voltage (e.g. ~12 V), whereas a linear charger is the