User's Manual

Smart Machine Smart Decision
SIM868_Hardware_Design_V1.00 20 2016-06-20
4. Application Interface
4.1. Power Supply
The power supply range of SIM868 is from 3.4V to 4.2V. 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
/GPS_VBAT input, a bypass capacitor (low ESR) such as a 100 µF is strongly recommended.
For the VBAT/GPS_VBAT input, a 100uF Tantalum capacitor (CA low ESR) and a 1uF~10uF Ceramics
capacitor CB are 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
SIM868 VBAT pins.
Figure 5: Reference circuit of the VBAT/GPS_VBAT input
Table 7: Recommended zener diode
Vendor Part number Power(watts) Packages
1 On semi MMSZ5231BT1G 500mW SOD123
2 Prisemi PZ3D4V2H 500mW SOD323
3 Vishay MMSZ4689-V 500mW SOD123
4 Crownpo CDZ55C5V1SM 500mW 0805
The following figure is the reference design of +5V input power supply. The output power supply is 4.1V, thus a
linear regulator can be used.
Figure 6: Reference circuit of the LDO power supply