DSB75 Development Support Board Rev. B1 Hardware Description
Confidential / Released
DSB75_hd_v12
Page 65 of 96
2008-08-26
shunt resistors R602 and R603).
The battery voltage is measured at the VSENSE line.
The battery temperature is measured at the BATTEMP line (voltage drop at NTC in battery
pack).
The diode V603 prevents reverse battery discharging in fast charging path if the power
failed.
Current calculation:
The current will be ramped up and down by battery management and reaches the maximum
at V
ISENSE
= 150mV.
I
max
=150mV / 0.3Ohm = 500mA @ Jumper X600 open
=150mV / 0.15Ohm = 1A
@ Jumper X600 closed
5V0
Charging On
Trickle curent control
BATT+
BATT+
U
I
Charging current control
Ba
tte
ry
m
ana
gem
e
nt
A
D
MU
X
Sense
LDO
5.0V
Charger
supply
5V...8V
+
Control current
0...0.6mA
Trickle charge current 5mA or 30mA
Fast charge current
I=V
ISENSE
/(R603+R602)
DSB75
GSM module
+
-
+
-
+
-
+
-
B2B
X100
N600
R603
R602
X600
V601
V602
R6
04
V603
X710
X
7
00
,X
70
1
S6
01
S6
01
1,2
4,5
X602
3
T
ISENSE
CHARGEGATE
VSENSE
BATTEMP
VCHARGE
B ATT+
5mA or 30mA
m
ax
.15
0m
V
V
IS
EN
SE
0R15
0R15
1.2V
10k
PO
W
ER
6
ADC
3V3_4V5
BATT+
10k
4
3
1
1
2
3
Figure 38: Schematic of charging circuit
3.14.4
Real Time Clock Supply
A 100µF capacitor placed on the DSB75 is charged by the VDDLP line of the GSM module
as long as the voltage BATT+ is applied.
In case of power failure, the real time clock of the GSM module is supplied by the capacitor
for approx. 40 seconds.
