TOBY-L4 series - System Integration Manual
UBX-16024839 - R04
Design-in
Page 53 of 143
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 must 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-L4 series modules must be sourced through the
VCC
pins with a suitable DC power supply that should
meet the following prerequisites to comply with the modules’
VCC
requirements summarized in Table 7.
The suitable 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 > 5V?
Switching Step-Down
Regulator
No, portable device
No, less than 5 V
Yes, greater than 5 V
Yes, always available
Figure 19: 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-L4 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, 2.2.1.10, 2.2.1.11 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, 2.2.1.10, 2.2.1.11 for specific design-in.
If TOBY-L4 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, 2.2.1.10, 2.2.1.11 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 must 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 the
