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SIM800_Hardware Design_V1.10 21 2018-08-13
Vin
Vout
GND
FB
3
+
PWR_CTRL
R102
R101
VBAT
100K
43K
+
C103
330uF
C104
100nF
U101
MIC29302
5
4
1
2
C101 C102
100uF
1uF
DC INPUT
R103
470Ω
On/Off
Figure 6: Reference circuit of the power supply
If there is a high drop-out between the input and the desired output (VBAT), a DC-DC power supply will be
preferable because of its better efficiency. The following figure is the reference circuit. FB101 is very important,
customer can get better EMI feature with appropriate filtering bead.
Vin
Vout
FB
U101
1
2
3
4
5
LM2596- ADJ
+
100uH
MBR360
L101
C101
+
C102
D102 C103
R102
R101
FB101
330uF
VBAT
2.2K
1K
100uF
1uF
C104
100nF
DC INPUT
PWR_CTRL
GND
On/Off
c
Figure 7: Reference circuit of the DC-DC power supply
The single 3.7V Li-ion cell battery can be connected to SIM800 VBAT pins directly. But the Ni-Cd or Ni-MH
battery must be used carefully, since their maximum voltage can rise over the absolute maximum voltage of the
module and damage it.
When battery is used, the total impedance between battery and VBAT pins should be less than 150mΩ.
The following figure shows the VBAT voltage drop at the maximum power transmit phase, and the test condition
is as following:
VBAT=4.0V,
A VBAT bypass capacitor C
A
=100µF tantalum capacitor (ESR=0.7Ω),
Another VBAT bypass capacitor C
B
=1µF. (See C
A
and C
B
in figure 5)
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