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4 GSM Application Interface
4.1 Power Supply
The power supply range of SIM808 is from 3.4V to 4.4V.Recommended voltage is 4.0V.The transmitting burst
will cause voltage drop and the power supply must be able to provide sufficient current up to 2A. For the VBAT
input, a bypass capacitor (low ESR) such as a 100 µF is strongly recommended.
Increase the 33PF
and 10PF capacitors can effectively eliminate the high frequency interference. A 5.1V/500mW
Zener diode is strongly recommended, the diode can prevent chip from damaging by the voltage surge. These
capacitors and Zener diode should be placed as close as possible to SIM808 VBAT pins.
Figure 5: Reference circuit of the VBAT input
Table 6: Recommended Zener diode
Vendor Part number Power(watts) Packages
1 On semi MMSZ5231BT1G 500mW SOD123
2 Prisemi PZ3D4V2H 500mW SOD323
3 Prisemi PZ5D4V2H 500mW SOD523
4 Vishay MMSZ4689-V 500mW SOD123
5 Crownpo CDZ55C5V1SM 500mW 0805
The following figure is the reference design of +5V input power supply. The designed output for the power
supply is 4.1V, thus a linear regulator can be used.
SIM808_Hardware Design_V1.00 2014.03.27
20
Figure 6: Reference circuit of the LDO power supply
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