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FIBOCOM SC138-
NA
Series Hardware Guide
35/88
3 Application Interface
3.1
Power
SC138 provides 3 VBAT pins for connecting external power supply to the module. The range of power
input voltage is 3.5 V-4.2 V, and the recommended value is 3.8 V. The performance of module power
supply, such as load capacity and ripple size, will directly affect the performance and stability of the
module during normal operation. The peak current of the module can reach 3 A under limiting cases. If
the power supply capacity is insufficient and the power supply voltage falls to below 3 V, the module may
power off or restart. The power supply voltage drop is shown in the following figure:
Burst Transmit
Burst Transmit
3V
Drop
500mV
VBAT
3.5V
Figure 3-1 Voltage drop
3.1.1
Power Input
The external power supply supplies power to SC138 series modules through VBAT pins. In order to
ensure that the power supply voltage is no less than 3 V, it is recommended to parallel two 220 uF
tantalum capacitors with low ESR and filter capacitors of 1 uF, 100 nF, 39 pF 33 pF, etc. near the VBAT
input terminal, and the PCB routing of VBAT be as short and wide as possible (no less than 3 mm). The
ground plane of the power supply part should be as complete as possible to reduce the equivalent
impedance of VBAT routing, and ensure that there will not be too large falling of voltage under high-
current at the maximum transmitting power.
