User's Manual

XT55/56 Hardware Interface Description
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XT55/56_hd_v02.06a Page 90 of 125 17.12.2004
Table 27: Electrical description of application interface
Function Signal name IO Signal form and level Comments
GSM_BATT+ I V
I
= 3.3V to 4.8V
V
I
norm = 4.2V
Inorm  1.6A (during Tx burst)
Imax< 2A
GSM power
supply
GND
1 Tx, peak current 577µs every 4.616ms
2 Tx, peak current 1154µs every
4.616ms
Power supply input.
5 GSM_BATT+ pins to be
connected in parallel. 5 GND
pins to be connected in
parallel.
The power supply must be
able to meet the
requirements of current
consumption in a Tx burst
(up to 3A).
Sending with two timeslots
doubles the duration of
current pulses to 1154µs
(every 4.616ms)!
GSM_POWER I
V
I
min = 3.0V
V
I
max = 15V
This line signalizes to the
processor that the charger is
connected.
If unused keep pin open.
GSM_BATT_TEM
P
I
Connect NTC with R
NTC
 10kΩ @ 25°C
to ground.
Input to measure the battery
temperature over NTC
resistor.
NTC should be installed
inside or near battery pack to
enable the charging
algorithm and deliver
temperature values.
If unused keep pin open.
Charge
interface
GSM_CHARGE O
I
GSM_CHARGE
= -300µA ... -600µA
@ 3V < V
GSM_CHARGE
< V
LOAD
This line is a current source
for the charge FET with a
10kΩ resistance between
gate and source.
If unused keep pin open.
External
supply
voltage
GSM_VDD O
GSM_VDDmin = 2.84V,
GSM_VDDmax = 2.96V
Imax = -10mA
C
L
max = 1µF
Supply voltage, e.g. for an
external LED or level shifter.
The external digital logic
must not cause any spikes or
glitches on voltage
GSM_VDD.
Not available in POWER
DOWN mode.
GSM_VDD signalizes the
“ON” state of the module.
If unused GSM_VDD keep
pin open.
VDD Low
Power
GSM_VDDLP I/O
R
I
=1kΩ
V
O
max  4.0V (output)
V
I
min = 2.2V, V
I
max = 5.5V (input)
I
I
typ = 10µA at GSM_BATT+ = 0V
Mobile in POWER DOWN mode:
V
I
min = 1.2V
Supplies the RTC with power
via an external capacitor or
buffer battery if no V
GSM_BATT+
is applied.
If unused keep pin open.