Specifications

XT55 Hardware Interface Description
Confidential / Preliminary
s
mo b i l e
XT55_hd_v00.02 Page 40 of 116 17.03.2004
3.5 GSM charging control
The GSM/GPRS part of the XT55 module integrates a charging management for Li-Ion
batteries. You can skip this chapter if charging is not your concern, or if you are not using
the implemented charging algorithm.
XT55 has no on-board charging circuit. To benefit from the implemented charging
management you are required to install a charging circuit within your application. In this
case, XT55 needs to be powered from a Li-Ion battery pack, e.g. as specified in Table 8.
Note: The charging control described in this chapter is optimized for the GSM/GPRS part
of XT55 only and does not cover the GPS part. To include the GPS part you need to
change components illustrated in Figure 9, especially those of the trickle charging
path (470R, 4V3, 1SS355).
The module only delivers, via its GSM_POWER line and GSM_CHARGE line, the control
signals needed to start and stop the charging process. The charging circuit should include a
transistor and should be designed as illustrated in Figure 9. A list of parts recommended for
the external circuit is given in Table 7.
to GSM_BATT+
Input from
charger
(5.5V - 8V)
under load
CHARGE
470R
1SS355
3k3
100nF 10k
SI3441DV
4V3
1/
5
ESDA6V1-5W6
to POWER
GSM_BATT_TEMP
1/
5
ESDA6V1-5W6
NTC
+
Battery
pack
PCB spark
gap
CRS04
-
Figure 9: Schematic of approved charging transistor, trickle charging and ESD protection