User's Manual

Neo_M680 Hardware User Guide V1.0

Figure 7 Using PMOS for power control

Q2 is for eliminating the need for a high enough voltage level of the host GPIO. In case that the

GPIO can output a high voltage greater than VDD3V9 - |V

GS(th)

|, where V

GS(th)

is the Gate Threshold

Voltage, Q2 is not needed.

Reference components:

Q1: IRML6401

Q2: MMBT3904

C4: 470uF tantalum capacitor rated at 6.3V; or 1000uF aluminum capacitor.

It’s strongly recommended to place a TVS diode on VBAT to ground, in order to absorb the power

surges subjected. The SMAJ5.0A from Vishay can be as a choice.

6.1.2.2 Power Separating

As described in section 6.1.1, the GSM device works in burst mode generating voltage drops on

power supply. And furthermore this results in a 217Hz TDD noise through power (One of the way

generating noise. Another way is through RF radiation). Analog parts, especially the audio circuits,

are subjected to this noise, known as a “buzz noise” in GSM systems. To prevent other parts from

being affected, it’s better to use separated power supplies. The module shall be supplied by an