SIM340 Hardware Design
Figure 4: Reference circuit of the VBAT input
The circuit design of the power supply depends strongly from the power source where this power
is drained. The following figure is the reference design of +5V input source power supply. The
designed output for the power supply is 4V, thus a linear regulator can be used. If there’s a big
difference between the input source and the desired output (VBAT), a switching converter power
supply will be preferable because of its better efficiency especially with the 2A peak current in
burst mode of the module.
The single 3.6V Li-Ion cell battery type can be connected to the power supply of the SIM340
VBAT directly. 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.
Figure
5: 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.
SIM340_HD_V3.09
18.03.2009
23
