u-blox SARA-G3 Series System Integration Manual page 94

kHz must be carefully evaluated since this can produce noise in the VCC voltage profile and therefore
negatively impact GSM modulation spectrum performance. An additional L-C low-pass filter between the
switching regulator output to VCC supply pins can mitigate the ripple on VCC, but adds extra voltage
drop due to resistive losses on series inductors

PWM mode operation: it is preferable to select regulators with Pulse Width Modulation (PWM) mode.
While in connected-mode Pulse Frequency Modulation (PFM) mode and PFM/PWM mode, transitions
must be avoided to reduce the noise on the VCC voltage profile. Switching regulators that are able to
switch between low ripple PWM mode and high efficiency burst or PFM mode can be used, provided
the mode transition occurs when the module changes status from idle/active-mode to connected-mode
(where current consumption increases to a value greater than 100 mA): it is permissible to use a
regulator that switches from the PWM mode to the burst or PFM mode at an appropriate current
threshold (e.g. 60 mA)
 Output voltage slope: the use of the soft start function provided by some voltage regulators should be
carefully evaluated, since the VCC pins voltage must ramp from 2.5 V to 3.2 V within 4 ms to
switch on the module that otherwise can be switched on by a low level on PWR_ON pin
Figure 27Figure 27 and the components listed in
power supply circuit, where the module VCC is supplied by a step-down switching regulator capable of
delivering 1.9 A current pulses with low output ripple and with fixed switching frequency in PWM mode
operation greater than 1 MHz.
12V
5
R1 RUN
9
VC
10
RT
7
PG
R2 R3
6
SYNC
C1 C2 C3 C4 C5
Figure 27: Suggested schematic design for the VCC voltage supply application circuit using a step-down regulator
UBX-13000995 - R06
SARA-G3 series - System Integration Manual
Table 13Table 13
4
VIN
1
BD
2 C6
BOOST
L1
3
SW
D1
U1
R4
8
FB
GND
R5
11
Objective Specification
show an example of a high reliability
SARA-G3 series
51 VCC
VCC
52
53 VCC
C7 C8
GND
Page 94 of 218
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