TOBY-L2 and MPCI-L2 series - System Integration Manual
UBX-13004618 - R07
Advance Information
Design-in
Page 70 of 158
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 31) 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 31: 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
