SIM800L datasheet(21/73 Pages) SIMCOM

21 / 73 page

Smart Machine Smart Decision

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.

Figure 7: Reference circuit of the DC-DC power supply

The single 3.7V Li-ion cell battery can be connected to SIM800H&SIM800L 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 CA=100µF tantalum capacitor (ESR=0.7Ω),

Another VBAT bypass capacitor CB=1µF.

Figure 8: VBAT voltage drop during transmit burst

4.1.1.

Power Supply Pin

Pin 1 and Pin 42 are VBAT input, Pins 2,43,44,45 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.

SIM800H&SIM800L_Hardware Design_V2.02

2015-07-27

SIM800L 数据表(PDF) 21 Page - SIMCom