SARA-R4 series - System Integration Manual
UBX-16029218 - R06
Design-in
Page 41 of 102
GND
Power path management IC
Vout
Vin
θ
Li-Ion/Li-Pol
Battery Pack
GND
System
12 V
Primary
Source
Charge
controller
DC/DC converter
and battery FET
control logic
Vbat
Figure 14: Charger / regulator with integrated power path management circuit block diagram
Figure 15 and the components listed in Table 12 provide an application circuit example where the MPS MP2617
switching charger / regulator with integrated power path management function provides the supply to the
cellular module while concurrently and autonomously charging a suitable Li-Ion (or Li-Polymer) battery with
proper pulse and DC discharge current capabilities and proper DC series resistance according to the rechargeable
battery recommendations described in section 2.2.1.4.
The MP2617 IC constantly monitors the battery voltage and selects whether to use the external main primary
supply / charging source or the battery as supply source for the module, and starts a charging phase accordingly.
The MP2617 IC normally provides a supply voltage to the module regulated from the external main primary
source allowing immediate system operation even under missing or deeply discharged battery: the integrated
switching step-down regulator is capable to provide up to 3 A output current with low output ripple and fixed
1.6 MHz switching frequency in PWM mode operation. The module load is satisfied in priority, then the
integrated switching charger will take the remaining current to charge the battery.
Additionally, the power path control allows an internal connection from battery to the module with a low series
internal ON resistance (40 m
typical), in order to supplement additional power to the module when the current
demand increases over the external main primary source or when this external source is removed.
Battery charging is managed in three phases:
Pre-charge constant current
(active when the battery is deeply discharged): the battery is charged with a
low current, set to 10% of the fast-charge current
Fast-charge constant current
: the battery is charged with the maximum current, configured by the value
of an external resistor to a value suitable for the application
Constant voltage
: when the battery voltage reaches the regulated output voltage (4.2 V), the current is
progressively reduced until the charge termination is done. The charging process ends when the charging
current reaches the 10% of the fast-charge current or when the charging timer reaches the value configured
by an external capacitor
Using a battery pack with an internal NTC resistor, the MP2617 can monitor the battery temperature to protect
the battery from operating under unsafe thermal conditions.
Several parameters as the charging current, the charging timings, the input current limit, the input voltage limit,
the system output voltage can be easily set according to the specific application requirements, as the actual
electrical characteristics of the battery and the external supply / charging source: proper resistors or capacitors
have to be accordingly connected to the related pins of the IC.
