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SIM900D Hardware Design
Figure4: Reference circuit of the source power supply input
The following figure is the VBAT voltage drop at the maximum power transmit phase, the test condition is
VBAT=4.0V, VBAT maximum output current =2A, C
=100µF tantalum capacitor (ESR=0.7Ω) and C
=1µF.
A
B
577us
4.615ms
I
Burst:2A
VBAT
VBAT
Max:300mV
Figure5: VBAT voltage drop during transmit burst
3.3.1 Power Supply Pins
Two VBAT pins are dedicated to connect the supply voltage and nine GND pins are dedicated to connect ground.
VRTC pin can be used to back up the RTC.
3.3.2 Minimizing Power Losses
When designing the power supply for your application please pay specific attention to power losses. Ensure that
the input voltage VBAT never drops below 3.4V even in a transmit burst where current consumption can rise to
typical peaks of 2A. If the power voltage drops below 3.4V, the module may be switched off. The PCB traces
from the VBAT pins to the power source must be wide enough to decrease heat energy in the transmitting burst
mode.
23
SIM900D_HD_V1.02
09.04.2010
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