SimCom SIM900D EVB, Проектирование аппаратного обеспечения

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SIM900D Hardware Design
But the Ni_Cd or Ni_MH battery types must be used carefully, since their maximum voltage can rise over the
absolute maximum voltage for the module and damage it.
Figure4: Reference circuit of the source power supply input
The following figure is the VBAT voltage ripple wave at the maximum power transmit phase, the test condition is
VBAT=4.0V, VBAT maximum output current =2A, C
A
=100µF tantalum capacitor (ESR=0.7 Ω ) and C
B
=1µF.
Max:300mV
VBAT
Burst:2A
I
VBAT
4.615ms
577us
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 users design the power supply for their application, specific attention need to be paid to power losses.
Ensure that the input voltage VBAT never drops below 3.1V even in a transmit burst where current consumption
can rise to typical peaks of 2A. If the power voltage drops below 3.1V, the module may be shut down
automatically. The PCB traces from the VBAT pins to the power source must be wide enough to decrease heat
energy in the transmitting burst mode.
SIM900D_Hardware Design_V1.04 2010.10.09
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