User's Guide

ATOP3.5G Product Description
80447ST10636A rev.10 – 2015-03-03
Reproduction forbidden without written authorization from Telit Communications S.p.A. - All Rights
Reserved. Page 29 of 66
Mod. 0808 2011-07 Rev.2
9 Application design-in information
9.1 Battery charging
ATOP 3.5G natively handles Lithium Ion battery technology.
The charging algorithm supports three charging techniques: trickle charge, constant-current and
constant voltage. The charging state machine is mostly automated, with a minimum of software
intervention.
 The first step in the automated charging process determines if trickle charging is needed.
Charging of a severely depleted battery must begin with trickle charging to limit the current
and protect the battery from more charging current than it can handle.
 Once a minimum battery voltage is established using trickle charging, constant-current
charging is enabled to charge the battery quickly – this mode is sometimes called fast
charging.
 Once the battery approaches its target voltage, the charge is completed using constant-
voltage charging.
A battery thermistor sensor allows controlling the temperature window within which the charger is
active.
For characteristics of the charging process, refer to Sections 12.2 and 13.5.
Figure 7 shows the internal and external components involved in battery charging.
Figure 7 ATOP 3.5G battery charging
If no rechargeable battery is used in the application, the charging control pins must be connected
as follows:
 VCHG_SNK, BB_BATT_FET_N, BB_ICHG, and BB_BATT_THERM must be left unconnected
 VBAT_SENSE must be connect to VBAT_PA_SNK