N715-EA Hardware User Guide
Chapter 5 Application Interfaces
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In GSM/GPRS mode, RF data is transmitted in burst mode that generates voltage drops on the power supply.
Furthermore, this results in a 217 Hz TDD noise through the power and the transient peak current is 2.5 A.
Therefore, it is necessary to ensure that the drive capacity of the power supply is sufficient, the power supply
trace is wide enough to reduce impedance and there are large-capacity capacitors to improve the freewheeling
capability to ensure that the voltage will not drop below the minimum operating voltage of the module when the
instantaneous current reaches its peak.
Figure 5-1 Voltage drops of the power supply.
Burst
Burst
0.577msT2.038ms
Min: 3.3V
VBAT
VBAT3.4V
Drop
Never use a diode to make the drop voltage between a higher input and the module power supply. The forward
voltage drop V
f
of the diode has two characteristics: one is that it increases with the increase of forward current;
the other is that it increases significantly at a low temperature. If there is an instantaneous high current, the
instantaneous increase of forward voltage drop will lead to unstable operating voltage of the module, or even
damage the module.
The power supply design of the N715-EA module is determined by the power input voltage. The
designs are classified by power input voltage as follows:
⚫
Supports the 3.4 V - 4.2 V power input (typical value: 3.6 V, supplied by a battery)
⚫
Supports the 4.2 V - 5.5 V power input (typical value: 5.0 V, supplied by a computer through its
internal rectifier.)
⚫
Supports the 5.5 V - 24 V power input (typical value: 12 V, using a DC-DC power supply
solution.)
The recommended 3.4 V to 4.2 V input design is as follows:
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