Integration Manual

Table Of Contents
TOBY-L2 and MPCI-L2 series - System Integration Manual
UBX-13004618 - R26 Design-in
Page 72 of 162
typical choice when the charging source has a relatively low nominal voltage (~5 V). If both a permanent primary
supply / charging source (e.g. ~12 V) and a rechargeable back-up battery (e.g. 3.7 V Li-Pol) are available at the
same time in the application as possible supply source, then a proper charger / regulator with integrated power
path management function can be selected to supply the module while simultaneously and independently
charging the battery. See 2.2.1.7, 2.2.1.8 and 2.2.1.6, 2.2.1.9, 2.2.1.10 for specific design-in.
The use of a primary (not rechargeable) battery is in general uncommon, but appropriate parts can be selected
given that the most cells available are seldom capable of delivering the maximum current specified in TOBY-L2
series Data Sheet [1] during connected-mode. Carefully evaluate the usage of super-capacitors as supply source
since aging and temperature conditions significantly affect the actual capacitor characteristics. See 2.2.1.5 and
2.2.1.6, 2.2.1.9, 2.2.1.10 for specific design-in.
Rechargeable 3-cell Li-Ion or Li-Pol and Ni-MH chemistry batteries reach a maximum voltage that is above the
maximum rating for the 3.3Vaux supply of MPCI-L2 modules, and should therefore be avoided. The use of
rechargeable, not-rechargeable battery or super-capacitors is very uncommon for Mini PCI Express applications, so
that these supply sources types are not considered for MPCI-L2 modules.
The usage of more than one DC supply at the same time should be carefully evaluated: depending on the supply
source characteristics, different DC supply systems can result as mutually exclusive.
The following sections highlight some design aspects for each of the supplies listed above providing application
circuit design-in compliant with the module VCC requirements summarized in Table 7.
2.2.1.2 Guidelines for VCC or 3.3Vaux supply circuit design using a switching regulator
The use of a switching regulator is suggested when the difference from the available supply rail to the VCC or the
3.3Vaux value is high, since switching regulators provide good efficiency transforming a 12 V or greater voltage
supply to the typical 3.8 V value of the VCC supply or the typical 3.3 V value of the 3.3Vaux supply.
The characteristics of the switching regulator connected to VCC or 3.3Vaux pins should meet the following
prerequisites to comply with the module VCC or 3.3Vaux requirements summarized in Table 7:
Power capability: the switching regulator with its output circuit must be capable of providing a voltage value
to the VCC or 3.3Vaux pins within the specified operating range and must be capable of delivering to VCC
or 3.3Vaux pins the maximum peak / pulse current consumption during Tx burst at maximum Tx power
specified in the TOBY-L2 series Data Sheet [1] or in the MPCI-L2 series Data Sheet [2].
Low output ripple: the switching regulator together with its output circuit must be capable of providing a
clean (low noise) VCC or 3.3Vaux voltage profile.
High switching frequency: for best performance and for smaller applications it is recommended to select a
switching frequency 600 kHz (since L-C output filter is typically smaller for high switching frequency). The
use of 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 or 3.3Vaux voltage profile and
therefore negatively impact LTE/3G/2G modulation spectrum performance. An additional L-C low-pass filter
between the switching regulator output to VCC or 3.3Vaux supply pins can mitigate the ripple at the input
of the module, 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, the Pulse Frequency Modulation (PFM) mode and PFM/PWM modes transitions must be
avoided to reduce the noise on the VCC or 3.3Vaux voltage profile. Switching regulators can be used that
are able to switch between low ripple PWM mode and high ripple PFM mode, provided that the mode
transition occurs when the module changes status from the idle/active-modes to connected-mode. It is
permissible to use a regulator that switches from the PWM mode to the burst or PFM mode at an appropriate
current threshold.