Error! No text of specified style in document. - System Integration Manual
CDMA-2X-11004-P1
Objective Specification
System description
Page 19 of 79
Stress beyond the VCC absolute maximum ratings can cause permanent damage to the module: if
necessary, voltage spikes beyond VCC absolute maximum ratings must be restricted to
values within the specified limits by using appropriate protection.
When designing the power supply for the application, pay specific attention to power losses
and transients. The DC power supply must be able to provide a voltage profile to the VCC
pins with the following characteristics:
Voltage drop during transmission must be lower than 250 mV
Any degradation in power supply performance (due to losses, noise or transients) will
directly affect the RF performance of the module since the single external DC power source
indirectly supplies all the digital and analog interfaces, and also directly supplies the RF
power amplifier (PA).
5.3.2.1
VCC application circuits
Error! No text of specified style in document. modules must be supplied through the VCC pins by
one (and only one) proper DC power supply that must be one of the following:
Switching regulator
Low Drop-Out (LDO) linear regulator
Rechargeable Li-Ion 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 3: 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 Error! No text of specified style
in document. modules 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.
The use of an LDO linear regulator becomes convenient for a primary supply with a relatively low
voltage (e.g. less than 5 V). In this case the typical 90% efficiency of the switching regulator will
diminish the benefit of voltage step-down and no true advantage will be gained in input current
savings. On the opposite side, linear regulators are not recommended for high voltage step-down
as they will dissipate a considerable amount of energy in thermal power.
If Error! No text of specified style in document. 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 Lithium-Ion 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.
