SimCom SIM800 Hardware Design page 21

DC INPUT
+
C101 C102
100uF
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.
DC INPUT
+
C101
100uF
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:
SIM800_Hardware Design_V1.10
U101 MIC29302
2
Vin
1
On/Off
1uF
3
PWR_CTRL
Figure 6: Reference circuit of the power supply
LM2596- ADJ
U101
1
Vin Vout
5
C102
On/Off
1uF
PWR_CTRL
3
Figure 7: Reference circuit of the DC-DC power supply
VBAT=4.0V,
A VBAT bypass capacitor C
Another VBAT bypass capacitor C
21
4
Vout
5
R101
+
FB
100K
R102
43K
L101
2
100uH
+
4
FB
D102 C103
330uF
MBR360
c
=100µF tantalum capacitor (ESR=0.7Ω),
A
=1µF. (See C and C
B A
Smart Machine Smart Decision
VBAT
C103 R103
C104
470Ω
330uF 100nF
FB101
R101
C104
2.2K
100nF
R102
1K
in figure 5)
B
2018-08-13
VBAT