SARA-R4/N4 series - System Integration Manual
UBX-16029218 - R11 Design-in Page 66 of 157
2.2.1.7 Guidelines for external charging and power path management circuit
Application devices where 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 as a possible supply source,
should implement a suitable charger / regulator with integrated power path management function to supply
the module and the whole device while simultaneously and independently charging the battery.
Figure 23 reports a simplified block diagram circuit showing the working principle of a charger / regulator
with integrated power path management function. This component allows the system to be powered by a
permanent primary supply source (e.g. ~12 V) using the integrated regulator, which simultaneously and
independently recharges the battery (e.g. 3.7 V Li-Pol) that represents the back-up supply source of the
system. The power path management feature permits the battery to supplement the system current
requirements when the primary supply source is not available or cannot deliver the peak system currents.
A power management IC should meet the following prerequisites to comply with the module VCC
requirements summarized in Table 6:
High efficiency internal step down converter, with characteristics as indicated in section 2.2.1.2
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
VoutVin
θ
Li-Ion/Li-Pol
Bat t ery Pack
GND
Syst em
12 V
Primary
Source
Charge
cont roller
DC/DC converter
and bat t ery FET
cont rol logic
Vbat
Figure 23: Charger / regulator with integrated power path management circuit block diagram
Figure 24 and the parts listed in Table 16 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 2.2.1.4.
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.
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