LEON-G100 / LEON-G200 - System Integration Manual
GSM.G1-HW-09002-G3
Preliminary
System description
Page 18 of 125
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 5: 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 LEON-G100/LEON-G200 operating supply voltage. The use
of switching step-down provides the best power efficiency for the overall application and minimizes current
drawn from main supply source.
The use of an LDO linear regulator becomes convenient for primary supplies with relatively low voltage (e.g. less
than 5 V). In this case a switching regulator with a typical efficiency of 90% reduces the benefit of voltage
step-down for input current savings. Linear regulators are not recommended for high voltage step-down as they
will dissipate a considerable amount of power in thermal energy.
If the LEON-G100/LEON-G200 is deployed in a mobile unit with no permanent primary supply source available,
then a battery is required to provide
VCC
. A standard 3-cell Lithium-Ion battery pack directly connected to
VCC
is the typical choice for battery-powered devices. Batteries with Ni-MH chemistry should be avoided, since they
typically reach a maximum voltage during charging that is above the maximum rating for
VCC
.
The use of primary (disposable) batteries is uncommon, since the typical cells available are seldom capable of
delivering the burst peak current for a GSM call due to high internal resistance.
The following sections highlight some design aspects for each of these supplies.
Switching regulator
The characteristics of the switching regulator connected to the
VCC
pin should meet the following requirements:
Power capabilities
: the switching regulator with its output circuit must be capable of providing a proper
voltage value to the
VCC
pin and delivering 2.5 A current pulses with a 1/8 duty cycle to the
VCC
pin
Low output ripple
: the switching regulator and output circuit must be capable of providing a clean (low
noise) VCC voltage profile
High switching frequency:
for best performance and for smaller applications select a switching frequency
≥
600 kHz (since an L-C output filter is typically smaller for high switching frequency). Using a switching
regulator with a variable switching frequency or with a switching frequency lower than 600 kHz must be
carefully evaluated since this can produce noise in the
VCC
voltage profile and therefore impact and worsen
GSM modulation spectrum performance. An additional L-C low-pass filter between the switching regulator
output and the
VCC
supply pin can mitigate the ripple on
VCC,
but adds extra voltage drop due to resistive
losses in series inductors
PWM mode operation
: select preferably regulators with Pulse Width Modulation (PWM) mode. Pulse
Frequency Modulation (PFM) mode and PFM/PWM mode transitions while in active mode must be avoided
to reduce the noise on the
VCC
voltage profile. Switching regulators able to switch between low ripple
