Power Supply Pin - SIM Tech SIMCom SIM800C Hardware Design

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 especially with the 2A peak current in burst mode of the module. The
following figure is the reference circuit.
DC INPUT
FUSE
+
C101
100uF
The single 3.7V Li-ion cell battery can be connected to SIM800C 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:
577us
I
VBAT
VBAT
4.1.1.

Power Supply Pin

Pin34 and Pin35 are VBAT input, Pin36 and Pin37 are GND of power supply, VRTC pin is power supply of the
RTC circuit in the module. VDD_EXT output 2.8V when module is in normal operation mode.
When designing the power supply in customer's application, pay special attention to power losses. Ensure that
the input voltage never drops below 3.0V even when current consumption rises to 2A in the transmit burst. If the
power voltage drops below 3.0V, the module may be shut down automatically. The PCB traces from the VBAT
pins to the power supply must be wide enough (at least 60mil) to decrease voltage drops in the transmit burst.
The power IC and the bypass capacitor should be placed to the module as close as possible.
SIM800C_Hardware_Design_V1.00
U101 LM2596- ADJ
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
4.615ms
Figure 8: VBAT voltage drop during transmit burst
L101
2
100uH
+
4
FB
D102 C103
330uF
MBR360
=100µF tantalum capacitor (ESR=0.7Ω),
A
=1µF.
B
18
Smart Machine Smart Decision
FB101
VBAT
270
Ω
R101
C104
2.2K
100nF
R102
1K
Burst:2A
Max:350mV
2014-10-30