TOBY-L1 and MPCI-L1 series - System Integration Manual
UBX-13001482 - R04
Advance Information
Design-in
Page 38 of 90
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, 2.2.1.7, 2.2.1.8, 2.2.1.9 for specific design-in.
Keep in mind that the use of batteries requires the implementation of a suitable charger circuit (not included in
TOBY-L1 series modules). The charger circuit should be designed in order to prevent over-voltage on
VCC
beyond the upper limit of the absolute maximum rating. See section 2.2.1.7 for specific design-in.
The use of primary (not rechargeable) battery or super-capacitors is in general uncommon, but appropriate parts
can be selected given that the most parts available are seldom capable of delivering the maximum current
specified in
TOBY-L1 series Data Sheet
[1] during the RF transmission in connected-mode. Carefully evaluate the
usage of super-capacitors as supply source since aging and temperature conditions significantly affect the actual
capacitor characteristics. See sections 2.2.1.5, 2.2.1.6, 2.2.1.8, 2.2.1.9 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-L1 series 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-L1 series 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
and
3.3Vaux
requirements summarized in Table 7.
2.2.1.2
Guidelines for VCC 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
3.3Vaux
value is high, since switching regulators provide good efficiency transforming a 12 V or greater voltage
supply to a suggested ~4.1 V value for the
VCC
supply or a suggested ~3.44 V value for 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
withstanding and delivering the maximum current specified in
TOBY-L1 series Data Sheet
[1] or
MPCI-L1
[2] when in connected-mode.
•
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 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 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, 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
(where the current consumption increases to a value greater than 200 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. 100 mA).
