TOBY-L2 and MPCI-L2 series - System Integration Manual
UBX-13004618 - R28
Design-in
Page 69 of 164
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
The proper DC power supply can be selected according to application requirements (see
between different possible supply source types, of 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
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
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
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
