TOBY-L1 and MPCI-L1 series - System Integration Manual
UBX-13001482 - R04
Advance Information
Design-in
Page 37 of 90
2.2
Supply interfaces
2.2.1
Module supply (VCC or 3.3aux)
2.2.1.1
General guidelines for VCC 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-L1 and MPCI-L1 series modules must be sourced through the
VCC
or the
3.3Vaux
pins with a proper DC
power supply that should meet the prerequisites to comply with the
VCC
or
3.3aux
requirements summarized in
Table 7.
The proper DC power supply can be selected according to the application requirements (see Figure 19) 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
Main Supply
Available?
Battery
Li-Ion 3.7 V
Linear LDO
Regulator
Main Supply
Voltage
>5 V?
Switching
Step-Down
Regulator
No, portable device
No, less than 5 V
Yes, greater than 5 V
Yes, always available
Figure 19: VCC / 3.3Vaux supply concept selection
The DC/DC 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 modules
VCC
or
3.3aux
operating supply voltage.
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 sections 2.2.1.2, 2.2.1.6, 2.2.1.8, 2.2.1.9 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 sections 2.2.1.3, 2.2.1.6, 2.2.1.8, 2.2.1.9 for specific design-in.
If TOBY-L1 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
