LEXI-R422 - System integration manual
UBX-23007449 - R02
Design-in
Page 41 of 108
C1-Public
A power management IC should meet the following prerequisites to comply with the module
VCC
requirements summarized in
•
High efficiency internal step down converter, with characteristics as indicated in section
•
Low internal resistance in the active path Vout
–
Vbat, typically lower than 50 m
•
High efficiency switch mode charger with separate power path control
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 22: Charger / regulator with integrated power path management circuit block diagram
and the parts listed in
provide an application circuit example where the MPS
MP2617H switching charger / regulator with integrated power path management function provides
the supply to the cellular module. At the same time it also concurrently and autonomously charges a
suitable Li-Ion (or Li-Polymer) battery with the correct pulse and DC discharge current capabilities and
the appropriate DC series resistance according to the rechargeable battery recommendations
described in section
The MP2617H 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 MP2617H 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.
