Shenzhen Coban Electronics Co. Ltd. CB900 Manuale Utente
4.3. Power Supply and Ground
The power supply design is one of the key design areas for a GSM terminal due to the burst
characteristics of GSM transmission. The supply must be able to deliver very high current peaks in
a very short time during a GSM transmit burst, typically up to 2A. During these bursts, it is
recommended that the voltage drop does not exceed 400mV. The voltage ripple should not exceed
50mV at frequencies up to 200 kHz and 2mV at frequencies above 200 kHz. This might cause the
module to reset.
All four legs of the shield must be soldered onto the target PCB. The ground connection of
the target PCB has to go through a full ground plane on the PCB.
Power Supply Voltage
The power supply voltage for VBATT is given below:
49
GPIO61
I/O
General Purpose IO
Not to float
50
UTXD2
O
Serial data transmit
Not to float
51
URXD2
I
Serial data receive
Not to float
52
EINT0
I
External interrupt input
Not to float
53
GPIO16
I/O
General Purpose IO
Not to float
54
KCOL3
I
Keyboard input
Not to float
55
KCOL0
I
Keyboard input
Not to float
56
KCOL2
I
Keyboard input
Not to float
57
KROW4
I
Keyboard input
Not to float
58
KROW3
I
Keyboard input
Not to float
59
GND
60
NC
61
GND
62
KCOL4
I
Keyboard input
Not to float
63
KROW0
I
Keyboard input
Not to float
64
KROW2
I
Keyboard input
Not to float
65
SCL28
I/O
I2C clock line
Not to float
66
SDA28
I/O
I2C data cable
Not to float
67
URXD1
I
Serial data receive
Not to float
68
UTXD1
O
Serial data transmit
Not to float
Power Supply
Parameters
Conditions
Min
Type
Max
Unit
VBAT
Supply Voltages
Voltage measured at the VBAT pin. If
voltage drops below 3.5V, the module
will automatically power off.
3.5*
4.2
4.6
V
Voltage Drop
Normal condition with max transmitter
output
400
mV