Smart Machine Smart Decision
SIM800C_Hardware_Design_V1.02 18 2015-4-27
following figure is the reference circuit.
Vin
Vout
FB
U101
1
2
3
4
5
LM 2596-A D J
+
100uH
MBR360
L101
C 101
+
C 102
D 102 C 103
R 102
R 101
FB 101
330uF
VBAT
2.2K
1K
100uF
1uF
C 104
100nF
270
DC input
PW R_CTRL
GND
Ω
O n /O ff
Figure 7: Reference circuit of the DC-DC power supply
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 150m.
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=0.7),
Another VBAT bypass capacitor C
B
=1uF~10uF.
577us 4.615m s
B u rs t:2 A
I
VBAT
VBAT
M ax:350m V
Figure 8: VBAT voltage drop during transmit burst
4.1.1. Power Supply Pin
Pin34 and Pin35 are VBAT input, Pin36 and Pin37 are GND of power supply, and 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 customers’ 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.
VBAT
MIN:3.0V
Figure 9: The minimal VBAT voltage requirement at VBAT drop
Note: Hardware power off voltage is 3.0V.
To Next Page
Loading...
Need help?
General
