DSB75 Development Support Board Rev. B1 Hardware Description
Confidential / Released
DSB75_hd_v12
Page 64 of 96
2008-08-26
Table 29: Pin assignment of the X700 jack for the plug-in charger
Pin no.
Name
I/O
Description
1 GND
-
Ground
2
R
-
4.7k resistor to pin 3 (necessary for old charger types)
3 V
Charge
I
Supply voltage provided by the plug-in charger
4 -12
-
-
Not relevant for charger (keep not connected)
Table 30: Pin assignment of the X701 jack for the plug-in charger
Pin no.
Name
I/O
Description
1 V
Charge
I
Supply voltage provided by the plug-in charger
2 GND
-
Ground
3 -12
-
-
Not relevant for charger (keep not connected)
3.14.3.2 Charging
Circuit
If a battery is used, it is possible to charge the battery by the charger circuitry on the DSB75.
The charger circuitry provides trickle charge to the battery when the mobile is in deep
discharge lockout or undervoltage lockout (when the battery condition is not suitable), and
provides fast charging at normal charging conditions.
This section describes the charging circuit of the DSB75 only. The battery management and
charging algorithm is described in [1]. Figure 38 shows the charging circuit of DSB75.
For supplying the GSM module by battery the toggle switch S601 must be flipped up to
connect the module’s supply voltage pin BATT+ to the battery and to be ready for
connecting the external charger.
The jumper X710 selects either the voltage from the external charger or the 5V0 board
voltage for battery charging.
Trickle Charging:
The 5.0V LDO regulator N600 protects the VCHARGE line against not allowed voltages >5V.
The diode V600 prevents reverse battery discharging if the charger is removed. The GSM
module delivers the trickle current back to the battery if a valid battery is recognized
chargeable and VCHARGE > V
BATT+.
There are two trickle charge currents possible: 5mA (battery is deep discharged) or 30mA
(battery has undervoltage).
Fast Charging:
The charge current is controlled by the GSM module (via CHARGEGATE). The
CHARGEGATE is a current sink (operation range 0…0.6mA). Because CARGEGATE needs
overvoltage protection (>4.5V), FET V601 reduces the control voltage.
V
CHARGEGATE
= V
BATT+
- V
GS(V601)
= max
3.5V
The CHARGEGATE control current flows through the R604. This resistor determines the
gate source voltage V
GS(V602)
. The value of R604 is dimensioned for driving the maximal fast
charge current of 1A at 0.5mA control current. In this case the fast-charging-FET V602
reaches only the beginning of the saturation region.
The current is measured differentially via the sense lines VSENSE, ISENSE (voltage drop at
