User's Manual

TOBY-R2 series - System Integration Manual
UBX-16010572 - R04 Design-in
Page 66 of 147
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.
TOBY-R2 series modules must be sourced through the VCC pins with a proper DC power supply that should
meet the following prerequisites to comply with the modules’ VCC requirements summarized in Table 6.
The proper DC power supply can be selected according to the application requirements (see Figure 27) 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 > 5V?
Switching Step-Down
Regulator
No, portable device
No, less than 5 V
Yes, greater than 5 V
Yes, always available
Figure 27: 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-R2 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 sections 2.2.1.2, 2.2.1.6, 2.2.1.11, 2.2.1.12 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, 2.2.1.11, 2.2.1.12 for specific design-in.
If TOBY-R2 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, 2.2.1.6, 2.2.1.7, 2.2.1.11, 2.2.1.12 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, 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