User's Manual

L811-EA Module Hardware User Manual Page
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5 Hardware Interface
5.1 Power Interface
5.1.1 Power Supply
The L811-EA module requires a 3.3V - 4.5V DC power supply that capable of supplying maximum GSM
emission current which may up to 2A.
Input power supply requirements:
Parameter
Minimum Value
Recommended Value
Maximum Value
Unit
VBAT
3.3
3.8
4.4
V
Important notes for the power supply:
1. Voltage fluctuation of the power supply should be lower than 200mV.
2. VBAT should not lower than 3.3V when the voltage dropping occurs.
The filtering capacitors for designing the power supply as shown in the following tables:
Recommended
capacitance
Application
Description
330uF
Power supply
Reduce voltage fluctuation during the phone call.
For capacitance value, the bigger the better.
1uF,100nF
Digital signal noise
Filter for the interference caused by clock and
digital signals.
39pF,33pF
700 /850 /900 MHz
Filter for RF interference.
18pF,8.2pF,6.8pF
1700/1800/1900,
2100/2600MHz
Filter for RF interference.
5.1.2 VSD2_1V8
VSD2_1V8 is the power source of the internal digital circuits, it can be also used as the power indicator
and the reference voltage. For circuit design, it can be only used for low current application (<50mA),
floating if not used.